NAVY SS600-A3-MMA-010/53833 MARINE CORPS TM 09603B-14&P/ LP REVISION 1

Transcription

1 NAVY SS600-A3-MMA-010/53833 MARINE CORPS TM 09603B-14&P/ LP REVISION 1 TECHNICAL MANUAL MAINTENANCE MANUAL ORGANIZATIONAL LEVEL MK 25 MOD 2 UNDERWATER BREATHING APPARATUS (UBA) DISTRIBUTION STATEMENT D: DISTRIBUTION AUTHORIZED TO U.S. DEPARTMENT OF DEFENSE AND U.S. DOD CONTRACTORS ONLY; ADMINISTRATIVE/OPERATIONAL USE; (15 MARCH 2006). OTHER REQUESTS FOR THIS DOCUMENT SHALL BE REFERRED TO PROGRAM EXECUTIVE OFFICE, LITTORAL AND MINE WARFARE (PEO LMW) (PMS NSW), 614 SICARD STREET SE, WASHINGTON NAVY YARD, DC DESTRUCTION NOTICE: FOR UNCLASSIFIED, LIMITED DOCUMENTS DESTROY BY ANY METHOD THAT WILL PREVENT DISCLOSURE OF CONTENTS OR RECONSTRUCTION OF THE DOCUMENT. PUBLISHED BY DIRECTION OF PROGRAM EXECUTIVE OFFICE, LITTORAL AND MINE WARFARE

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3 NAVY SS600-A3-MMA-010/53833 MARINE CORPS TM 09603B-14&P/ LP REVISION 1 TECHNICAL MANUAL MAINTENANCE MANUAL ORGANIZATIONAL LEVEL MK 25 MOD 2 UNDERWATER BREATHING APPARATUS (UBA) DISTRIBUTION STATEMENT D: DISTRIBUTION AUTHORIZED TO U.S. DEPARTMENT OF DEFENSE AND U.S. DOD CONTRACTORS ONLY; ADMINISTRATIVE/OPERATIONAL USE; (15 MARCH 2006). OTHER REQUESTS FOR THIS DOCUMENT SHALL BE REFERRED TO PROGRAM EXECUTIVE OFFICE, LITTORAL AND MINE WARFARE (PEO LMW) (PMS NSW), 614 SICARD STREET SE, WASHINGTON NAVY YARD, DC DESTRUCTION NOTICE: FOR UNCLASSIFIED, LIMITED DOCUMENTS DESTROY BY ANY METHOD THAT WILL PREVENT DISCLOSURE OF CONTENTS OR RECONSTRUCTION OF THE DOCUMENT. PUBLISHED BY DIRECTION OF PROGRAM EXECUTIVE OFFICE, LITTORAL AND MINE WARFARE 15 MARCH 2006

4 LIST OF EFFECTIVE PAGES INSERT LATEST CHANGED PAGES. DESTROY SUPERSEDED PAGES. Dates of issue for original and changed pages are: Original October 1998 Revision March 2006 NOTE: The portion of the text affected by changes is indicated by a vertical line in the outer margins of the page. Changes to illustrations are indicated by miniature pointing hands. Changes to diagrams are indicated by shaded areas. TOTAL NUMBER OF PAGES IN THIS PUBLICATION IS 226, CONSISTING OF THE FOLLOWING: Page No. *Change No. Page No. *Change No. Title... 0 List of Effective Pages... 0 Change Record i... 0 Change Record ii blank... 0 i thru x thru thru blank thru blank thru blank thru blank thru thru thru thru blank blank blank blank blank blank blank blank blank blank blank blank blank blank blank thru Appendix A Title... 0 blank... 0 A-1 thru A A-4 blank... 0 * Zero in this column indicates an original page. REVISION 1

5 CHANGE RECORD CHANGE NO. DATE TITLE AND/OR BRIEF DESCRIPTION SIGNATURE OF VALIDATING OFFICER REVISION 1 Change Record-i/(Change Record-ii blank)

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7 TABLE OF CONTENTS Chapter Page LIST OF ILLUSTRATIONS...iv LIST OF TABLES... v FOREWORD...vi LIST OF ABBREVIATIONS AND ACRONYMS...vii SAFETY SUMMARY...ix CHAPTER 1 GENERAL INFORMATION AND SAFETY PRECAUTIONS SAFETY PRECAUTIONS Standards Special Safety Notations Additional Safety and Information Advisories INTRODUCTION Purpose Scope SYSTEM DESCRIPTION Principal Components Alternative Principal Components REFERENCE DATA EQUIPMENT, ACCESSORIES, AND DOCUMENTS SUPPLIED PUBLICATION REFERENCES CHAPTER 2 OPERATION INTRODUCTION Scope Mission Considerations Carbon Dioxide Scrubber Canisters and Absorbents Canister Duration Limits MK 25 MOD 2 UBA CONTROLS AND INDICATORS Pneumatic Subsystem Controls and Indicators Recirculation Subsystem Control OPERATING PROCEDURES Premission Checkout/Ready for Issue (RFI) Procedures Initial Equipment Setup Predive Checkout Purge Procedures Additional Precautions Diving Supervisor Final Check EMERGENCY PROCEDURES Oxygen Toxicity REVISION 1 i

8 Chapter TABLE OF CONTENTS - Continued System Flooding Bypass Knob or Demand Valve Stuck Open Breathing Gas Pressure Deficiency Demand Valve Failure (Automatic or Bypass) ACCIDENT/INCIDENT EQUIPMENT STATUS REPORT POSTDIVE PROCEDURES CHECKLISTS AND PROCEDURES CHAPTER 3 FUNCTIONAL DESCRIPTION INTRODUCTION General Description Component Alternatives Component Function and Location PRINCIPAL COMPONENTS DESCRIPTION Pneumatic Subsystem Recirculation Subsystem Equipment Housing Subsystem CHAPTER 4 SCHEDULED MAINTENANCE INTRODUCTION GENERAL SAFETY AND ENVIRONMENTAL PRECAUTIONS Maintenance Safety Oxygen-Safe Area Hazardous Material Disposal Instructions MK 25 MOD 2 UBA MAINTENANCE LOG Reentry Control (REC) Procedures Failure Analysis Reporting Maintenance History Form MAINTENANCE REQUIREMENTS Repair Parts Test Equipment and Tools Torque Specifications Cleaning and Sanitizing Lubricants SCHEDULED MAINTENANCE PROCEDURES Maintenance Index Page CHAPTER 5 TROUBLESHOOTING INTRODUCTION BACKGROUND FAILURE REPORTING TROUBLESHOOTING INDEX Page ii REVISION 1

9 Chapter TABLE OF CONTENTS - Continued CHAPTER 6 CORRECTIVE MAINTENANCE INTRODUCTION MK 25 MOD 2 UBA FAILURE REPORTING Routine Failure Analysis Reporting Accident/Incident Reporting CORRECTIVE MAINTENANCE PROCEDURES CHAPTER 7 PARTS LISTS INTRODUCTION MAJOR ASSEMBLIES AND COMPONENTS PARTS LISTS AND ILLUSTRATIONS MK 25 Mod 2 UBA DVD Contract LIST OF MANUFACTURERS CHAPTER 8 INSTALLATION INTRODUCTION INVENTORY OPERATIONAL READINESS TOOLS AND TEST EQUIPMENT APPENDIX A MK 25 MOD 2 UBA SWITCHOVER PURGE PROCEDURES... A-1 Page REVISION 1 iii

10 LIST OF ILLUSTRATIONS Figure Title Page Figure 1-1. MK 25 Mod 2 UBA in Donned Position (Front View) Figure 1-2. Front View of Assembled MK 25 Mod 2 UBA Unit Figure 1-3. Circulation Diagram (As Worn) Figure 2-1. MK 25 Mod 2 UBA Controls and Indicator Locations (As Worn) Figure 2-2. MK 25 Mod 2 UBA Major Component Locations (As Worn) Figure 2-3. Ready for Issue (RFI) Log Figure 2-4. Predive Checklist (Sheet 1 of 2) Figure 2-5. Attachment of Inhalation Hose to Breathing Bag Model 2A Figure 2-6. Postdive Checklist (Sheet 1 of 2) Figure 3-1. Recirculation and Pneumatic Component Locations (As Worn) Figure 4-1. Reentry Control Boundaries Block Diagram Figure 4-2. Reentry Control Form, MK 25 Mod 2 UBA Figure 4-3. Reentry Control Log, MK 25 Mod 2 UBA Figure 4-4. Maintenance History Form (Sample) Figure 4-5. Torque Adjustment Figure 5-1. Gas Leaks in Cylinder Valve or Cylinder to Valve Interface Figure 5-2. Gas Leaks in Oxygen Reducer (Common) Figure 5-3. Leaks in Oxygen Reducer Model 2A Figure 5-4. Leaks in Oxygen Reducer Model 2B Figure 6-1. MK 25 Mod 2 UBA FAR Figure 6-2. Breathing Bag and Bag Seal Figure 6-3. Placement of Tabs Figure 6-4. Safety Valve Test Assembly Figure 6-5. Reducer Model 2B Safety Relief Valve Test Assembly Figure 6-6. Reducer Model 2B Intermediate Pressure Test Assembly Figure 7-1. MK 25 Mod 2 UBA Principal Components (Location Reference Only) Figure 7-2A. Oxygen Reducer Model 2A Figure 7-2B. Oxygen Reducer Model 2B Figure 7-3. Demand Valve Assembly Figure 7-4. Connecting Line Assembly Figure 7-5. Standard Pressure Gauge Line Assembly Figure 7-6. Cylinder Valve Assembly Figure 7-7. Oxygen Cylinder Figure 7-8. Soda Lime Canister, Mod 2 (Urethane) Figure 7-9. Inhalation/Exhalation/Mouthpiece Assemblies Figure 7-10A. Breathing Bag Assembly Model 2A Figure 7-10B. Reserved for Future Use Figure 7-11A. Equipment Housing, Fiberglass Figure 7-11B. Equipment Housing, Urethane Figure Flexible Gauge Line Kit iv REVISION 1

11 LIST OF TABLES Table Title Page Table 1-1. MK 25 Mod 2 UBA Technical and Functional Characteristics Table 1-2. Equipment, Accessories, and Documents Supplied Table 1-3. Publication References (Not Supplied with the MK 25 Mod 2 UBA) Table 2-1. MK 25 Mod 2 UBA Controls and Indicator Functions Table 2-2. Figures/Checklists and Tables/Procedures Index Table 2-3. MK 25 Mod 2 UBA Subsystem and Component List Table 2-4. Premission Checkout Procedures Table 2-5. Initial Setup Procedures Table 2-6. Predive Checkout Procedures Table 2-7A. Purge Procedure Decision Tree Table 2-7B. Predive/Surface Transit Purge Procedure Table 2-7C. Emergency Descent Purge Procedure Table 2-7D. Underwater Purge Procedures (Other than SDV Scenarios) Table 2-8. Doffing Procedures Table 2-9. Postdive Maintenance Procedures Table 4-1. MK 25 Mod 2 UBA Tools, Test Equipment, and Repair Kits Table 4-2. MK 25 Mod 2 UBA Torque Specifications Table 4-3. MK 25 Mod 2 UBA Cleaning Procedures Table 5-1. Index of Troubleshooting Procedures Table 6-1. Corrective Maintenance Index Table 6-2. Disassemble/Reassemble Recirculation Subsystem Table 6-3. Replace Standard Pressure Gauge Line Assembly Table 6-4. Replace Connecting Line Assembly Table 6-5. Repair Breathing Hose Assemblies Table 6-6. Replace One-Way Valve Disc Table 6-7. Repair Mouthpiece Valve Table 6-8. Repair Breathing Bag Model 2A Table 6-9. Replace Cylinder Valve in Oxygen Cylinder Table Repair Cylinder Valve Table 6-11A. Repair Oxygen Reducer Model 2A Table 6-11B. Repair Oxygen Reducer Model 2B and Flexible Gauge Table Repair Mod 2 (Urethane) Soda Lime Canister Table 6-13A. Replace Standard Pressure Gauge Table 6-13B. Install Flexible Gauge Line Kit Table Repair Demand Valve and Lead Shot Pouch Assembly Table Paint Oxygen Cylinder Table 8-1. Operational Readiness Inspection REVISION 1 v

12 FOREWORD This technical manual contains procedures for operation and maintenance of the MK 25 Mod 2 Underwater Breathing Apparatus (UBA). The information in this manual is presented in eight chapters and an appendix. General information and safety precautions are provided in Chapter 1; operational procedures in Chapter 2; a functional description in Chapter 3; maintenance and troubleshooting procedures in Chapters 4, 5, and 6; parts lists in Chapter 7; and installation information in Chapter 8. Appendix A contains the MK 25 Mod 2 UBA Switchover Purge Procedures. Special Operations Forces, Marine Corps, ships, training activities, supply points, depots, Naval Shipyards, and Supervisors of Shipbuilding are requested to arrange for the maximum practical use and evaluation of Naval Sea Systems Command (NAVSEA) technical manuals. All errors, omissions, discrepancies and suggestions for improvement to NAVSEA technical manuals shall be submitted using the Technical Manual Deficiency/Evaluation Report (TMDER). All TMDERs are forwarded to the Naval System Data Support Activity (NSDSA), Port Hueneme Division Naval Surface Warfare Center. All comments will be thoroughly investigated and originators will be advised of action resulting from the submissions. Submit TMDER via the NSDSA website at Additional copies of this technical manual may be procured using standard stock requisitioning procedures. The National Stock Number of this manual, as recorded on the cover of the manual, is 0910-LP vi REVISION 1

13 LIST OF ABBREVIATIONS AND ACRONYMS Abbreviation/Acronym Definition 3-M Maintenance and Material Management ANU C CAGE cc CCW CGA CID CNS CONUS CW DLA DOT DSN DVD F FAR fsw ft-lb GSA HP IAW in. in-lb ISEA kg lb MIP mm MRC N/A NAVOSH NAVSEA NAVXDIVINGU NID N-m NOC NSDSA Authorized for U.S. Navy Use Degrees Celsius Commercial and Government Entity Cubic centimeter Counterclockwise Compressed Gas Association Commercial Item Description Central Nervous System Continental United States Clockwise Defense Logistics Agency Department of Transportation Defense Switched Network Direct Vendor Delivery Degrees Fahrenheit Failure Analysis Report Feet of seawater Foot-pound General Services Administration High-Pressure In Accordance With Inch Inch-pound In-Service Engineering Agent Kilogram Pound Maintenance Index Page Millimeter Maintenance Requirement Card Not Applicable Navy Occupational Safety and Health Naval Sea Systems Command Navy Experimental Diving Unit Nonionic Detergent Newton-meter Navy Oxygen Cleaner Naval System Data Support Activity REVISION 1 vii

14 LIST OF ABBREVIATIONS AND ACRONYMS - Continued Abbreviation/Acronym NSN NSW NSWC PC OPNAVINST PMS PMS NSW PN PQS psig REC RFI SDV SPMIG TMDER UBA Definition National Stock Number Naval Special Warfare Naval Surface Warfare Center Panama City Operational Navy Instruction Planned Maintenance System Naval Special Warfare Program Office Part Number Personnel Qualification Standard Pounds per square inch, gauge Reentry Control Ready for Issue SEAL Delivery Vehicle Standard PMS Materials Identification Guide Technical Manual Deficiency/Evaluation Report Underwater Breathing Apparatus viii REVISION 1

15 SAFETY SUMMARY GENERAL SAFETY PRECAUTIONS This manual describes physical and chemical processes that may cause injury or death to personnel, or damage to equipment if not properly followed. This safety summary includes general safety precautions and instructions that must be understood and applied during operation and maintenance to ensure personnel safety and protection of equipment. These general safety precautions are not related to specific procedures and therefore do not appear elsewhere in this publication. Prior to performing any task, the WARNING, CAUTION, and NOTE statements included in that task shall be reviewed and understood. STANDARD SAFETY PRECAUTIONS Operating and maintenance personnel must observe all applicable safety regulations and standard diving safety precautions as set forth in the U.S. Navy Diving Manual, SS521-AG-PRO-010 Revision 5, dated 15 August 2005, NSN 0910-LP FORCES AFLOAT Forces afloat must also comply with the Navy Occupational Safety and Health (NAVOSH) Program Manual for Forces Afloat, Operational Navy Instruction (OPNAVINST) series. SHORE ACTIVITIES Shore activities must also comply with the NAVOSH Program Manual, OPNAVINST series. HIGH-PRESSURE OXYGEN MAINTENANCE SAFETY In addition to other safety precautions prescribed in this manual, maintenance shall be performed in accordance with the following general instructions, as appropriate. a. Keep sparks and flames away from oxygen systems. Shut down electrical equipment in immediate area during maintenance and work on oxygen systems. b. Before working on pneumatic components, ensure that the cylinder valve on oxygen cylinder is shut and pressure is vented from pneumatic subsystem. c. Exercise extreme care when handling high-pressure cylinders. Ensure that the cylinders are adequately protected from being dropped and from other abuse that would cause structural damage or create stress risers. If a cylinder is dropped or otherwise abused, the cylinder and valve shall be inspected in accordance with Maintenance Requirement Card (MRC) A-1R. OXYGEN SAFE AREA Components requiring oxygen (O 2 ) related maintenance, repair, or cleaning must be disassembled, cleaned, repaired, and reassembled in a designated "O 2 safe" area with the following minimum requirements: Work area must be enclosed. Work area must be free of oil and grease. Work area must be as free as possible of dust and debris. Work surface must be clean and nonporous. Personnel traffic must be restricted to the area. Work area must be well lighted. Tools shall be clean and designated for "O 2 USE ONLY." Personnel's hands, faces, and clothing shall be clean. Area shall be clearly marked: "Restricted - O 2 safe area" and "No smoking, eating or drinking." REVISION 1 ix

16 HAZARDOUS MATERIAL DISPOSAL INSTRUCTIONS Each unit shall comply with its own ship/station procedures for handling disposal of hazardous materials/waste identified in the MRCs. WARNINGS, CAUTIONS AND NOTES WARNING and CAUTION statements are used in this manual to highlight operating or maintenance procedures, practices, conditions, or statements that are considered essential to protection of personnel (WARNING) or equipment (CAUTION). WARNING and CAUTION statements immediately precede the step and procedure to which they apply. WARNING and CAUTION statements consist of four parts: heading (WARNING or CAUTION), a statement of the hazard, minimum precautions, and possible result if disregarded. NOTE statements are used in this manual to highlight operating or maintenance procedures, practices, conditions, or statements that are not essential to protection of personnel or equipment. NOTE statements may precede or follow the step or procedure, depending upon the information to be highlighted. The headings used and their definitions are as follows: WARNING Highlights an essential operating or maintenance procedure, practice, condition, statement, etc., which if not strictly observed, could result in long term health hazards, injury, or death to personnel. CAUTION Highlights an essential operating or maintenance procedure, practice, condition, statement, etc., which if not strictly observed, could result in damage to, or destruction of, equipment or loss of mission effectiveness. NOTE Highlights an essential operating or maintenance procedure, condition, or statement. x REVISION 1

17 CHAPTER 1 GENERAL INFORMATION AND SAFETY PRECAUTIONS 1.1 SAFETY PRECAUTIONS. Personnel using the MK 25 Mod 2 Underwater Breathing Apparatus (UBA) shall observe the safety precautions and procedures specified in this technical manual. Personnel must be thoroughly familiar with all safety procedures and understand the potential hazards associated with use of high-pressure oxygen equipment before using it or performing maintenance on it. All diving accidents/incidents related to the use of this equipment must be expeditiously reported by message in accordance with Operational Navy Instruction (OPNAVINST) series Chapter A6, and the U.S. Navy Diving Manual. The Commander, Naval Sea Systems Command (NAVSEA), SEA 00C3, will assist diving units with investigations and data collection following a diving mishap. Contact them at commercial (202) Standards. Standard safety precautions apply to diving operations as stated in the U.S. Navy Diving Manual. Only authorized sealants and lubricants selected for their compatibility with high-pressure oxygen systems shall be used. Substitution of parts or materials and omission or alteration of recommended procedures are not authorized. Diving safety and successful operation of the MK 25 Mod 2 UBA (Figure 1-1) depend upon the following: a. Competence and performance of operation. b. Operations planning. c. Adherence to approved operating, emergency, and maintenance procedures Special Safety Notations. Refer to the Safety Summary for safety notations Additional Safety and Information Advisories NAVSEA Diving Advisories. Occasionally NAVSEA 00C issues safety warnings and/or advisories pertaining to diving operation or to some specific diving equipment (MK 25 UBA and life preservers included). These Diving Advisories are forwarded to all diving units via Naval message format. The information contained in the Diving Advisory must be strictly adhered to, and the Diving Advisories must be on-hand and accessible at all times. The Diving Advisories are posted on the NAVSEA 00C3 website at MK 25 UBA In-Service Engineering Agent (ISEA) Notes. When warranted, the MK 25 UBA ISEA will notify users of updated information concerning components, maintenance, and procedures for the MK 25 Mod 2 UBA and life preservers. These ISEA Notes are forwarded to all MK 25 users via Naval message format. The ISEA Notes have the concurrence of NAVSEA 00C3 and 00C4 (System Certification Authority), as well as the Naval Special Warfare Program Office (PMS NSW). These Notes authorize certain changes in information and/or procedure, and must be on hand and accessible at all times. The MK 25 UBA ISEA Notes are posted on the Naval Special Warfare (NSW) web page at Always refer to the MK 25 UBA ISEA Notes and NAVSEA 00C Diving Advisories prior to operating or maintaining the MK 25 Mod 2 UBA. The MK 25 ISEA, as designated by PMS NSW, is: Naval Surface Warfare Center Panama City Attn: Code S13 (MK 25 UBA ISEA) 110 Vernon Avenue Panama City, Florida REVISION 1 1-1

18 SS600-A3-MMA-010/53833 Figure MK 25 Mod 2 UBA in Donned Position (Front View). REVISION 1

19 1.2 INTRODUCTION. This manual contains the technical information necessary to operate, maintain, troubleshoot, and repair the MK 25 Mod 2 UBA (Figure 1-2). It is not the intent of this manual to detail diving procedures and policy. Refer to the U.S. Navy Diving Manual and applicable Diving Advisories for diving policy Purpose. The purpose of this manual is to provide information that will enable diving personnel to operate and maintain the MK 25 Mod 2 UBA safely and efficiently Scope. The information in this manual is presented in eight chapters and one appendix. Chapter 1, "General Information and Safety Precautions," provides an introductory description of the MK 25 Mod 2 UBA system, operational configurations, characteristics, and design parameters. Chapter 2, "Operation," presents detailed system operational procedures in tabular form. Included are premission and predive checkout procedures, setup procedures, performance requirements within the operational environment, emergency procedures, accident/incident reporting, and postdive maintenance procedures. Chapter 3, "Functional Description," contains an explanation of how the equipment works, with detailed descriptions of the principle components of the system and their interrelationship within the system. Chapter 4, "Scheduled Maintenance," discusses the Planned Maintenance System (PMS) and reentry control. Chapter 4 also identifies tools, test equipment, torque specifications, cleaning procedures, lubricants, and documentation requirements for MK 25 Mod 2 UBA maintenance actions. Chapter 5, "Troubleshooting," is a guide to equipment fault isolation. It is presented in tabular and flowchart form, listing symptoms, probable causes, and suggested corrective actions. Chapter 6, "Corrective Maintenance," includes failure reporting, corrective maintenance actions, and repair procedures for the MK 25 Mod 2 UBA. Chapter 7, "Parts Lists," consists of part location, illustrations and an index of part names and numbers to assist in ordering spares for the MK 25 Mod 2 UBA. Chapter 8, "Installation," addresses the process of receiving and testing the initial issue of the MK 25 Mod 2 UBA. Appendix A contains MK 25 Mod 2 UBA Switchover Purge Procedures. REVISION 1 1-3

20 Figure 1-2. Front View of Assembled MK 25 Mod 2 UBA Unit. 1.3 SYSTEM DESCRIPTION. The MK 25 Mod 2 UBA is a self-contained, closed-circuit, 100-percent oxygen UBA designed for use by Special Operations Forces and the Marine Corps in shallow water operations where concealment of surface exhaust bubbles is essential. The MK 25 Mod 2 UBA is worn on the diver's chest with the breathing bag in the same relative position as the lungs. Figure 1-1 shows a diver wearing the MK 25 Mod 2 UBA. An assembled apparatus is shown in Figure REVISION 1

21 1.3.1 Principal Components. The following principal components of the MK 25 Mod 2 UBA are contained in the equipment housing: pressure regulator (reducer), associated piping, demand valve, respiratory (breathing) bag, and soda lime canister (carbon dioxide scrubber). The oxygen cylinder, inhalation and exhalation hoses, and the mouthpiece valve are external principal components. The breathing gas flows from the oxygen cylinder through the reducer and the automatic demand valve into the breathing bag. High-pressure gas goes to the pressure gauge, while intermediate (low) pressure gas goes to the demand valve. The swimmer inhales gas from the breathing bag and exhales into the soda lime canister (scrubber) where carbon dioxide is removed. Purified gas returns from the canister to the breathing bag to repeat the cycle. The gas flow from the breathing bag to the swimmer to the canister is in a counterclockwise direction, as illustrated in Figure 1-3. OXYGEN (LOW-PRESSURE) OXYGEN (HIGH-PRESSURE) BAR (145-3,000 PSIG) BREATHING GAS FLOW THROUGH RECIRCULATION SUBSYSTEM Figure 1-3. Circulation Diagram (As Worn) Alternative Principal Components. This technical manual addresses many new principal components introduced for the MK 25 Mod 2 UBA. The new components are direct replacements for the current components. The overall system performance of the UBA remains the same regardless of which combination of components is used (see Chapter 3 for descriptions of all principal components). For ease of identification, the current principal components are labeled "Model 2A" and, where applicable, the new components are labeled "Model 2B." REVISION 1 1-5

22 1.4 REFERENCE DATA. Table 1-1 summarizes the technical and functional characteristics of the MK 25 Mod 2 UBA. Principal component technical specifications are located in Chapter 3. Table 1-1. MK 25 Mod 2 UBA Technical and Functional Characteristics. Technical/Functional Area UBA Dimensions Length Width Height Aluminum Transport Case (approx.) Weight Length Width Height In air In water Operating time (based on oxygen cylinder charged to full capacity): Diving depth: Temperature: Diving Transport Gas type: Oxygen Characteristic inches (in.) (463 millimeters [mm]) in. (336 mm) 7.00 in. (177 mm) 22.5 in. (572 mm) 14.5 in. (368 mm) 9.5 in. (241 mm) pounds (lb) ( kilogram [kg]) depending on component configuration Neutral (with approximately 2 liters of oxygen in breathing bag) See canister duration limits, paragraph to 50 feet of seawater (fsw) (0.0 to 15.2 meters of seawater) 32 degrees Fahrenheit ( F) to 90 F (0 degrees Celsius [ C] to 32 C) -22 F to 120 F (-30 C to 49 C) Aviator s oxygen in accordance with (IAW) Performance Specification MIL-PRF REVISION 1

23 1.5 EQUIPMENT, ACCESSORIES, AND DOCUMENTS SUPPLIED. Equipment, accessories, and documents supplied with the MK 25 Mod 2 UBA are listed in Table 1-2. Table 1-2. Equipment, Accessories, and Documents Supplied. Qty Item Name Reference Number 1 MK 25 Mod 2 UBA MK 25 Mod 2US UBA 1 Kit, Field Mod 2 PN Cylinder Valve Cap PN S Part Number (PN) (converted) PN (production) 1 Reducer Plug PN /PN Planned Maintenance System (PMS) Maintenance Index Page (MIP) Maintenance Requirement Cards (MRCs) 1 Maintenance Manual, Organizational Level MIP 5921/182 NAVY SS600-A3-MMA-010/53833 MARINE CORPS TM 09603B-14&P/1 The MK 25 Mod 2 UBA is manufactured and supported by: Draeger Safety, Inc. 101 Technology Drive Pittsburgh, PA REVISION 1 1-7

24 1.6 PUBLICATION REFERENCES. Table 1-3 provides a list of publications, which are required for operation and maintenance but are not supplied with the MK 25 Mod 2 UBA. Where applicable, Internet websites have been referenced to aid the user in accessing pertinent information. Table 1-3. Publication References (Not Supplied with the MK 25 Mod 2 UBA). Publication Title Navy Occupational Safety and Health Ships' Maintenance and Material Management (3-M) Manual Naval Ship's Technical Manual (Chapter 593, Pollution Control) Naval Ship's Technical Manual (Chapter 262, Lubricating Oils, Grease, Specialty Lubricants and Lubricant Systems) U.S. Navy Diving Manual Volume 1: Diving Principles and Policies Volume 2: Air Diving Operations Volume 3: Mixed Gas Surface Supplied Diving Operations Volume 4: Closed-circuit and Semi Closed-circuit Diving Operations Volume 5: Diving Medicine and Recompression Chamber Operations U.S. Navy Diving and Manned Hyperbaric Systems Safety Certification Manual Diving Equipment Authorized for U.S. Navy Use NAVSEA 00C Diving Advisories MK 25 Mod 2 UBA Canister Duration Limits MK 25 UBA ISEA Notes Publication Number / Web Sites OPNAVINST 5100 Series OPNAVINST Series S9086-T8-STM-010/CH-593R4 S9086-H7-STM-010/CH-262R4 NAVSEA SS521-AG-PRO-010* (Available as a download PDF file only). * Revision 5, dated 15 August 2005, NSN 0910-LP NAVSEA SS521-AA-MAN (00C4 Certification) NAVSEA Ser 00C32/3062 of 26 July (00C3 Diving) NAVSEA 00C3 Letter 3151 Ser 00C34 / 3160 of 27 September 2001 (Confidential) REVISION 1

25 CHAPTER 2 OPERATION 2.1 INTRODUCTION Scope. This chapter presents the procedures necessary to prepare, set up, and operate the MK 25 Mod 2 Underwater Breathing Apparatus (UBA) efficiently and effectively. The procedures appear in tables and checklists containing step-by-step instructions. The tables can be used as instructional aids and the checklists can be used on the dive site to guide equipment preparation. The chapter presents operating information and procedures as follows: Controls and indicators Operating procedures: premission checkout/ready for issue, initial equipment setup, predive checkout (including storage and transportation of prepared UBA), basic purge procedures, additional precautions, and Diving Supervisor final check Emergency procedures Accident/incident equipment status report Postdive procedures. In addition to complying with the operating information in this manual, Diving Supervisors must comply with the guidelines presented in the U.S. Navy Diving Manual concerning oxygen exposure limits, medical aspects, planning guidelines, and the conduct of closed-circuit oxygen diving. WARNING Failure to perform any operating procedures presented herein may result in equipment failure and possible injury or death to operating personnel Mission Considerations. In addition to standard predive guidelines, mission requirements for using the MK 25 Mod 2 UBA must be considered. The MK 25 Mod 2 UBA is designed for use by Special Operations Forces and the Marine Corps in shallow water operations and must be used with an approved life preserver. Only life preservers authorized for use with the MK 25 Mod 2 UBA, as cited in the current Diving Equipment Authorized for U.S. Navy Use (ANU List), shall be used. The current ANU may be accessed at (00C3 Diving) Carbon Dioxide Scrubber Canisters and Absorbents. WARNING Use only NAVSEA Authorized for Navy Use (ANU) carbon dioxide absorbents with the MK 25 Mod 2 UBA. Failure to comply may result in diver injury or death. Two scrubber canisters are currently approved for use in the MK 25 Mod 2 UBA. The first, designated the "Mod 0" canister, is the older model and is fabricated from fiberglass. This canister is no longer manufactured, but is approved for continued use within the MK 25 Mod 2 UBA. The second, or "Mod 2", canister is fabricated of molded urethane. This is the newer model canister and can be completely disassembled to aid in cleaning the screens and center rod of absorbent build-up. See Chapter 3 for more detailed descriptions of these canisters. REVISION 1 2-1

26 WARNING Do not use 8-12 mesh absorbent in the Mod 0 (fiberglass) scrubber canister. The internal design of this canister allows the smaller size absorbent to migrate past the upper screen, which may cause diver injury if inhaled. There are currently four carbon dioxide absorbents approved for use in the MK 25 Mod 2 UBA. Note that 8-12 mesh absorbent is not approved for use with the Mod 0 (fiberglass) canister. The absorbents by brand name and distributor are: Absorbent/Distributor High Performance Sodasorb, Regular (Non-indicating), 4-8 mesh WR Grace & Co. Sofnolime 4-8 Mesh NI, L-Grade O.C. Lugo Sofnolime 8-12 Mesh NI, D-Grade O.C. Lugo DiveSorb Pro, 5-8 Mesh Draeger Safety, Inc. Use in Mod 0 (fiberglass) Canister YES YES NO YES Use in Mod 2 (urethane) Canister YES YES YES YES WARNING Exceeding authorized canister duration limits for given temperatures can result in unacceptable carbon dioxide levels in the breathing gas, resulting in diver injury or death. NOTE For canister duration limits, refer to NAVSEA 00C letter 3151 Ser 00C34/3160 of 27 September 2001 (Confidential). For a copy of this letter, contact NAVSEA 00C3 at (202) or send a request via their website Canister Duration Limits. In closed-circuit diving systems, the effective duration of the carbon dioxide absorbent is dependent on water temperature. Typically, absorbent duration will decrease as water temperature decreases. To extend the life of the absorbent in colder water (below 60 F), the canister is equipped with a removable insulator package. The insulator consists of a two-part, external neoprene boot and may be used on either the Mod 0 (fiberglass) or Mod 2 (urethane) canister. The insulator is recommended when diving in water cooler than 60 F, and mandatory for water temperatures below 40 F. To offset the positive buoyancy of the neoprene, 3.18 pounds of removable weight are fitted at the demand valve. The two weight pouches slide into pockets specifically designed for the MK 25 Mod 2 UBA. 2-2 REVISION 1

27 2.2 MK 25 MOD 2 UBA CONTROLS AND INDICATORS. Diver-operated controls on the MK 25 Mod 2 UBA permit the diver to adjust the breathing functions. The diver controls the breathing gas supply with the mouthpiece rotary valve. During descent or to purge the unit, the diver controls the gas flow to the breathing bag with the demand valve bypass knob. The pressure gauge indicates the amount of oxygen remaining in the oxygen cylinder. Table 2-1 describes the functions of the MK 25 Mod 2 UBA controls and indicators, and Figure 2-1 identifies their locations. WARNING The MK 25 Mod 2 UBA pressure reducer has an operating range of 10 to 207 bar (145 to 3,000 pounds per square inch, gauge [psig]). Reducer reaction is unpredictable at cylinder pressure less than 10 bar. The MK 25 Mod 2 UBA has no positive reserve. Gas supply pressure must be monitored via a pressure gauge provided for this purpose. NOTE The MK 25 Mod 2 UBA pressure gauge may be calibrated in bar not psig. Divers must assess remaining gas supply by multiplying the actual gauge reading by 14.5 to obtain psig (i.e., 14.5 x actual gauge reading [bar] equals psig) Pneumatic Subsystem Controls and Indicators. The oxygen cylinder valve (Figure 2-1 and Table 2-1) (4) controls the flow of high-pressure gas from the oxygen cylinder. The oxygen cylinder valve, when open, allows the high-pressure gas to flow to a reducer, which reduces the oxygen gas pressure to an intermediate level. The gas flows from the reducer to the demand valve, which contains a bypass knob (3). The bypass knob is used to bypass the automatic function of the demand valve when necessary to manually add oxygen to the breathing loop. The pressure gauge (2) indicates the amount of oxygen remaining in the oxygen cylinder Recirculation Subsystem Control. The mouthpiece rotary valve (Figure 2-1 and Table 2-1) (1) is the only diver-operated control in the recirculation subsystem. Located in the mouthpiece valve assembly, the rotary valve supplies breathing gas when placed in the dive (up) position and isolates the gas flow loop from the ambient atmosphere when placed in the surface (down) position. 2.3 OPERATING PROCEDURES. This paragraph provides detailed information concerning operating procedures, as well as information on postdive procedures. All specific procedures and checklists are located in paragraph 2.7, Checklists and Procedures, for ease of retrieval. Each checklist is presented first, followed by detailed procedures for that checklist. Each checklist is designed so that it can easily be laminated and reused, or photocopies may be made and used. Use of laminated copies or photocopies is at command discretion. Table 2-2, located in paragraph 2.7, provides a quick reference of checklists and procedures. Operating procedures for the MK 25 Mod 2 UBA can be categorized into four segments, listed below. More detailed purge procedures are located in Appendix A. a. Premission checkout procedures. (Table 2-4) b. Initial setup procedures. (Table 2-5) c. Predive checkout procedures. (Table 2-6) d. Basic purge procedures. (Table 2-7A thru 2-7D) REVISION 1 2-3

28 Knowledge of MK 25 Mod 2 UBA component function and location is crucial. Refer to Chapter 3 for component functions, and Figure 2-2 and Table 2-3 (paragraph 2.7) for component location. Table 2-1. MK 25 Mod 2 UBA Controls and Indicator Functions. Index No. Name Type Position Function 1 Mouthpiece valve assembly (with rotary valve) Lever handle Up (open) Down (closed) DIVE (up) position, supplies gas. SURFACE (down) position, isolates gas flow loop from ambient air and water conditions. 2 Standard pressure gauge Flexible pressure gauge Pressure indicator 0 to 350 bar (5,075 psig) 0 to 230 bar (3,335 psig) Indicates amount of oxygen remaining in oxygen cylinder. 3 Bypass knob (reverse of demand valve) Push button Depressed (open) Allows diver to bypass demand valve and to purge apparatus when necessary. 4 Oxygen cylinder valve Handwheel CCW (open) CW (shut) Controls flow of high-pressure oxygen from oxygen cylinder to reducer. CCW-counterclockwise; CW-clockwise. Figure 2-1. MK 25 Mod 2 UBA Controls and Indicator Locations (As Worn). 2-4 REVISION 1

29 CAUTION Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions Premission Checkout/Ready for Issue (RFI) Procedures. Mission: A deployment, a specific training exercise, or a series of dives conducted within a specific course of instruction, such as a combat swimmer course. Prior to any MK 25 Mod 2 UBA mission, each UBA must meet minimum requirements for RFI status. At the command level, all outstanding preventive maintenance must be completed for each UBA. In addition, premission checkout procedures in accordance with Table 2-4, Premission Checkout Procedures, must be accomplished. Upon completion of preventive maintenance and premission checkout, all UBA serial numbers for that mission shall be listed on the RFI Log (Figure 2-3). The MK 25 UBA technician certifies all necessary procedures have been performed, and deficiencies resolved, for each UBA listed. A hard copy of the RFI log accompanies the UBAs on the mission. Once completed, the RFI log remains in effect for the duration of the mission. If the RFI log is completed in preparation for a deployment, it is imperative each UBA listed be stored in a dry, secure container pending initial setup and predive procedures Initial Equipment Setup. Prior to initial equipment setup, the Diving Supervisor must verify the UBA is recorded on the RFI log. The MK 25 Mod 2 UBA initial setup process is recorded on the first section of Figure 2-4, Predive Checklist, and is accomplished according to procedures described in Table 2-5, Initial Setup Procedures. The initial setup includes procedures to inspect and service the MK 25 Mod 2 UBA equipment. During the initial setup, all components and parts are to be inspected for dirt, deterioration, damage, and residual water. The diver, or an authorized team member, must initial each step of the Predive Checklist after its completion to affirm that the procedure has been accomplished Predive Checkout. Following the initial setup of the MK 25 Mod 2 UBA, the apparatus is subjected to the predive checkout process, which is performed with the Diving Supervisor. Equipment checks and preparation procedures performed prior to the diver donning the equipment are recorded on the second section of Figure 2-4, Predive Checklist, and are presented in Table 2-6, Predive Checkout Procedures. The diver and the Diving Supervisor sign the Predive Checklist upon completion of both the initial setup and the predive checkout procedures. Once the MK 25 Mod 2 UBA Predive Checklist has been completed, the UBA is ready to dive Storage of Prepared MK 25 Mod 2 UBA. WARNING Storage procedures are authorized only if using 4-8 mesh carbon dioxide absorbent. Storage is not authorized for 8-12 mesh absorbent. Failure to comply may result in diver injury or death. If 4-8 mesh carbon dioxide absorbent is used, the UBA may be stored for up to 14 days prior to diving. Prior to storage, shut the oxygen cylinder valve and depress the demand valve bypass knob to vent the pneumatics subsystem. Deplete the breathing bag and place the mouthpiece rotary valve in the surface (closed) position. In this configuration, the UBA is airtight and the carbon dioxide absorbent in the canister is protected from moisture. Include a laminated or hard copy of the completed Predive Checklist (Figure 2-4) with the stored UBA. Storage is not authorized for 8-12 mesh carbon dioxide absorbents. REVISION 1 2-5

30 NOTE If stored in excess of 14 days, the carbon dioxide absorbent in the canister must be changed. High temperatures during transport and storage should not adversely affect carbon dioxide absorbents; however, storage temperatures below freezing may decrease performance and should be avoided. Check the manufacturer s recommendations regarding storage temperatures. In the event an operation calls for an oxygen dive followed by a surface interval and a second oxygen dive, the MK 25 Mod 2 UBA shall be sealed during the surface interval as described above (mouthpiece rotary valve in surface position, oxygen supply valve shut). It is not necessary to change carbon dioxide absorbent before the second dive as long as the combined canister durations of all subsequent dives do not exceed the canister duration limits specified Transportation of Prepared MK 25 Mod 2 UBA. For certain immediate-use missions, the MK 25 Mod 2 UBA must be shipped with a fully charged oxygen cylinder. The MK 25 Mod 2 UBA oxygen cylinder, composed of aluminum alloy T6061-T6, is manufactured and certified to Department of Transportation (DOT) 3AL specifications. Follow standard regulations for the shipment of such items; no additional documentation (i.e., Certificate of Equivalency) is required to ship the cylinder Purge Procedures. Any dive in which the MK 25 Mod 2 UBA is used requires that the diver perform a purge procedure to eliminate nitrogen from the UBA and the diver's lungs as soon as the diver begins breathing from the UBA. The purge prevents the possibility of hypoxia, a condition in which the partial pressure of oxygen in the UBA is too low to meet the metabolic needs of the body. The MK 25 Mod 2 UBA purge procedure produces an average oxygen fraction of 75 percent in the breathing loop. The actual purge procedure to be performed is dependent on the dive and mission. This chapter contains the basic, or most common, purge procedures for combat swimmers. Appendix A contains mission-specific purge procedures when using the SEAL Delivery Vehicle (SDV) Donning the UBA. Proper donning of the UBA ensures not only a proper purge, but makes the UBA more comfortable to wear and swim. The following are steps to ensure proper donning of the UBA: a. Attach the UBA harnesses so that the breathing bag is in the same relative position as the lungs (the top of the UBA should be 7 to 10 inches below the chin). b. Ensure UBA harnesses fit loosely enough to permit complete filling of the breathing bag. There should be a distance of one closed fist between the bag and the diver's chest. c. To prevent nitrogen from entering the breathing loop, ensure the facemask creates an airtight seal to the face Basic Purge Procedures. The term "basic" refers to the most common purge procedures used by combat swimmers. Three separate purge procedures fall into this category: a. Predive/Surface Transit Purge (main objective is to accomplish the purge just prior to the diver submerging). b. Emergency Descent Purge (used if an emergency descent is necessary prior to a proper surface purge being performed). c. Underwater Purge (switching from one UBA to the MK 25 Mod 2 UBA underwater, not in conjunction with SDV) Purge Procedure Decision Tree. The basic purge procedures are found in Tables 2-7B through 2-7D. Table 2-7A can aid in determining which purge procedure to use, based on the mission scenarios. Appendix A contains purge procedures specific to the SDV. 2-6 REVISION 1

31 Predive / Surface Transit Purge Procedure (Table 2-7B). Use this procedure if the MK 25 Mod 2 UBA is the only UBA used during the dive. Perform the procedure immediately before submerging (either on predive or after a surface transit) Emergency Descent Purge Procedure (Table 2-7C). Use this procedure if the MK 25 Mod 2 UBA is the only UBA used during the dive and an emergency descent prevents proper surface purge procedure from being completed. Perform this procedure immediately upon reaching depth Underwater Purge Procedures (Table 2-7D). Use this procedure if the dive was begun on another UBA using a breathing gas other than oxygen and the diver will begin breathing from the MK 25 Mod 2 UBA while at increased pressures less than 30 fsw. This procedure consists of the Surface Phase and the Pressurized Phase. Ensure Surface Phase is performed prior to Pressurized Phase Additional Purging. Once the MK 25 Mod 2 UBA dive has begun, additional purging is not necessary because significant nitrogen buildup does not occur. Additional purging should not be done during a dive for the following reasons: a. Additional purges consume more oxygen, thus decreasing the gas supply in the MK 25 Mod 2 UBA. b. The higher oxygen percentages that result from additional purging are not required to prevent hypoxia. c. Bubbles escaping during a purge procedure may cause a combat swimmer to be detected during a dive mission Precautions During the Purge Procedure. Do not perform the following purge procedure errors, which may result in a dangerously low percentage of oxygen in the MK 25 Mod 2 UBA. a. Exhaling back into mouthpiece with the last breath, rather than to the atmosphere while emptying the breathing bag. b. Underinflating the breathing bag during the fill segment of the fill/empty cycle. c. Adjusting the MK 25 Mod 2 UBA harnesses or life preserver straps too tightly to allow room for breathing bag expansion. This can result in underinflation of bag and inadequate purging. d. Failing to open oxygen cylinder valve prior to underwater purge procedures, causing breathing gas volume deficiency Additional Precautions. When diving the MK 25 Mod 2 UBA, special attention must be given to the mouthpiece rotary valve and the breathing bag to eliminate potential damage to the UBA and/or danger to the diver Mouthpiece Rotary Valve. The diver must close the mouthpiece rotary valve to the surface (down) position before removing the mouthpiece from the mouth. The mouthpiece should be maintained in the closed (surface) position while not in the mouth to prevent flooding of the breathing loop. Water entering the breathing loop will make the system inoperable since the canister (carbon dioxide scrubber) will not function when the absorbent is saturated with water. The water will also create a caustic slurry, which is harmful to the diver if ingested. WARNING The MK 25 Mod 2 UBA breathing bag does not have a dump valve, so overinflation may occur. Recharge the breathing bag at minimum possible depth; do not over inflate. Failure to comply may lead to increased exhalation resistance, causing diver injury or death. REVISION 1 2-7

32 Breathing Bag. The MK 25 Mod 2 UBA breathing bag, when normally inflated, is designed to hold an average lung capacity. When a diver inhales completely, the bag will deflate to approximately one-fifth of its normal size. If the bag is underinflated during inhalation, it will bottom out, triggering the demand valve to add a sufficient charge of oxygen Diving Supervisor Final Check. The Diving Supervisor performs the final check of the diver prior to the diver entering the water. The Diving Supervisor ensures that the initial equipment setup and predive checkout procedures have been completed and recorded on the Predive Checklist (Figure 2-4), and that the diver's equipment is properly donned, adjusted, and purged for the dive. At a minimum, the following checks on the MK 25 Mod 2 UBA are recommended: a. Ensure mouthpiece rotary valve is in dive (up) position. b. Verify proper operation of inhalation and exhalation one-way valves. c. Check UBA harnesses for proper donning and fit. d. Verify proper purge procedures were performed (if predive purge). e. Check oxygen pressure gauge for sufficient oxygen. 2.4 EMERGENCY PROCEDURES Oxygen Toxicity. a. Divers must be aware of the possibilities of central nervous system (CNS) oxygen toxicity when breathing pure oxygen under pressure. Signs and symptoms of CNS oxygen toxicity are described on the following page. These symptoms may occur singly or together. They occur in no particular order and there is no one symptom that could be considered more serious than another. V E N T I D C Visual symptoms Tunnel vision, a decrease in diver's peripheral vision, and other symptoms, such as blurred vision, may occur. Ear symptoms Tinnitus is any sound perceived by the ears but not resulting from an external stimulus. The sound may resemble bells ringing, roaring, or a machinery-like pulsing sound. Nausea or sporadic vomiting These symptoms may be intermittent. Twitching and tingling symptoms Any of the small facial muscles, lips or muscles of the extremities may be affected. This is the most frequent and obvious symptom. Irritability Any change in the diver's mental status, including confusion, agitation and anxiety. Dizziness Symptoms include clumsiness, uncoordination and unusual fatigue. Convulsions The first sign of CNS oxygen toxicity may be a convulsion that occurs with little or no warning. b. Diver Action: Notify dive buddy and make a controlled ascent to the surface while exhaling through the nose to prevent embolism. When on the surface, inflate the life preserver, shut the oxygen cylinder valve, close the mouthpiece rotary valve, remove the mouthpiece from mouth, and signal for assistance System Flooding. NOTE Use of the canister insulator may cause condensation to collect in the breathing bag or diaphragm chamber of the demand valve, causing a gurgling sound when using the UBA. Be familiar with all symptoms of system flooding. 2-8 REVISION 1

33 a. Symptoms include increased breathing resistance, gurgling sound, bitter taste in mouth (caustic cocktail), and possibly gas escaping from the system. b. Diver Action: Immediately attain a vertical position to keep the mouthpiece higher than the canister and activate the demand valve bypass knob. Notify dive buddy and make a controlled ascent to the surface while breathing in open circuit mode (breathe in from mouthpiece, exhale through nose). Maintain a vertical position while ascending and activate the bypass knob as necessary. When on the surface, inflate the life preserver, close the mouthpiece rotary valve, remove the mouthpiece from mouth, and signal for assistance. The oxygen cylinder valve shall remain open Bypass Knob or Demand Valve Stuck Open. a. Symptoms include increased exhalation resistance and an overabundance of gas accompanied by the sound of oxygen being added to the breathing bag. When the bypass knob is stuck open, the flow rate is approximately one liter/second. b. Diver Action: Notify dive buddy and make a controlled ascent to the surface while exhaling through the nose to prevent embolism. When on the surface, inflate the life preserver, shut the oxygen cylinder valve, close the mouthpiece rotary valve, remove the mouthpiece from mouth, and signal for assistance Breathing Gas Pressure Deficiency. a. Breathing gas pressure deficiency occurs when the UBA is not supplying an adequate amount of pressurized oxygen into the breathing loop to sustain the diver's needs. Symptoms include increased breathing resistance and deflation of the breathing bag. Probable causes range from low cylinder pressure to a malfunction in the oxygen cylinder valve, reducer, demand valve, or breathing loop. b. Diver Action: Notify dive buddy and make a controlled ascent to the surface while exhaling through the nose to prevent embolism. When on the surface, inflate the life preserver, close the mouthpiece rotary valve, remove the mouthpiece from mouth, and signal for assistance. The oxygen cylinder valve shall remain open Demand Valve Failure (Automatic or Bypass). a. Symptoms include demand valve failure to supply oxygen in either mode of operation. b. Diver Action: Notify dive buddy and make a controlled ascent to the surface while exhaling through the nose to prevent embolism. When on the surface, inflate the life preserver, close the mouthpiece rotary valve, remove the mouthpiece from mouth, and signal for assistance. The oxygen cylinder valve shall remain open. 2.5 ACCIDENT/INCIDENT EQUIPMENT STATUS REPORT. An accident is an unexpected event that culminates in loss of or serious damage to equipment or injury to personnel. An incident is an unexpected event that degrades safety and increases the probability of an accident. NOTE Accident/Incident status reporting criteria and procedures are available in the U.S. Navy Diving Manual, Volume 1, Chapter 5, Diving Program Administration and OPNAVINST series Chapter A6. Do not attempt to disassemble or otherwise tamper with the affected equipment. The number of diving accidents/incidents that involve MK 25 Mod 2 UBA users is small compared to the total number of dives conducted each year. However, critical UBA failures must receive a thorough review in order to identify the cause and determine the corrective measures to prevent further mishaps. In the event of an accident/incident, contact NAVSEA 00C3 immediately (commercial [202] ). NAVSEA 00C3 will assist diving units with investigations and data collection following a diving mishap. REVISION 1 2-9

34 NAVSEA 00C3 will assign a representative to inspect the initial condition of the equipment and to pick up or ship all pertinent records and equipment. Following removal of the affected equipment from the casualty, secure the oxygen cylinder valve and place the mouthpiece in the surface (closed) position. Place the equipment in a secure area to prevent any further handling of the equipment while awaiting an 00C3 representative. 2.6 POSTDIVE PROCEDURES. Upon completion of the dive, the diver exits the water and doffs the apparatus in accordance with the procedure described in Table 2-8, Doffing Procedures. After each use of the MK 25 Mod 2 UBA, perform the postdive maintenance procedures in accordance with Table 2-9, Postdive Maintenance Procedures, and record the results on the Postdive Checklist (Figure 2-6). For repetitive dives using the same MK 25 Mod 2 UBA, perform a complete postdive check only at the end of the dive day. The diver and Diving Supervisor sign the Postdive Checklist upon completion of the postdive maintenance procedures. 2.7 CHECKLISTS AND PROCEDURES. This section provides all predive and postdive checklists and procedures applicable to ensure proper operation of the MK 25 Mod 2 UBA. In each case, the checklist will appear first, followed by detailed procedures corresponding to each step on the list. Table 2-2 is a quick guide of all checklists and procedure tables presented in this section. Table 2-2. Figures/Checklists and Tables/Procedures Index. Figures / Checklist Page Figure 2-2. MK 25 Mod 2 UBA Major Component Locations (As Worn) 2-11 Figure 2-3. Ready For Issue (RFI) Log 2-13 Figure 2-4. Predive Checklist 2-17 Figure 2-5. Attachment of Inhalation Hose to Breathing Bag Model 2A 2-25 Figure 2-6. Postdive Checklist 2-33 Tables / Procedures Page Table 2-3. MK 25 Mod 2 UBA Subsystem and Component List 2-11 Table 2-4. Premission Checkout Procedures 2-14 Table 2-5. Initial Setup Procedures 2-19 Table 2-6. Predive Checkout Procedures 2-26 Tables 2-7A-D. Purge Procedures Table 2-8. Doffing Procedures 2-32 Table 2-9. Postdive Maintenance Procedures REVISION 1

35 Table 2-3. MK 25 Mod 2 UBA Subsystem and Component List. (Refer to Figure 2-2 for component locations.) Find Number Subsystem/Component 1-8 Recirculation Subsystem 1 Exhalation Hose 2 One-Way Exhaust Valve (Disc Valve) 3 Mouthpiece Valve Assembly (with Rotary Valve) 4 Head Strap 5 One-Way Inhalation Valve (Disc Valve) 6 Inhalation Hose 7A Breathing Bag Assembly, Model 2A (Connecting Pieces: CPI - Inhalation; CPDV - Demand Valve; CPC - Canister) 7B Reserved 8 Soda Lime Canister (CIP - Canister Intake Port; COP - Canister Outlet Port; CL - Canister Lid) 9-15 Pneumatic Subsystem 9A Standard Pressure Gauge 9B 10 Flexible Pressure Gauge Demand Valve/Bypass Knob (reverse not shown) CONVERTED UNIT (PN ) 11A Oxygen Reducer, Model 2A (HG - Reducer Hand Grip; SV Safety Valve Assembly) 11B Oxygen Reducer, Model 2B (HG Reducer Hand Grip; SV Safety Valve Assembly) 12 Connecting Line (Low-pressure) 13A Standard Pressure Gauge Line (High-pressure) 13B Flexible Pressure Gauge Line (High-pressure) 14 Oxygen Cylinder Valve (BD - Oxygen Cylinder Valve Safety Burst Disc) 15 Oxygen Cylinder Equipment Housing and UBA Harness 16A Equipment Housing (Fiberglass) (EH Exhalation Hose Slotted Indent; IH Inhalation Hose Slotted Indent) 16B Equipment Housing (Urethane) (EH Exhalation Hose Slotted Indent; IH Inhalation Hose Slotted Indent) 17 Cylinder/Canister Strap 18 Positioning Strap 19, 20 UBA Harness 21 Triglide PRODUCTION UNIT (PN ) 22 Lead Shot Pouch Kit 23 Canister Insulator 24 Cord Clip Figure 2-2. MK 25 Mod 2 UBA Major Component Locations (As Worn). REVISION /(2-12 blank)

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37 MK 25 MOD 2 UBA READY FOR ISSUE (RFI) LOG This MK 25 Mod 2 UBA RFI Log must be completed prior to any MK 25 Mod 2 UBA mission. Once completed, these UBAs are in a ready mode. This log remains in effect for the duration of the mission (as described in paragraph 2.3.1) and must accompany the UBAs during the mission. Mission: A deployment, a specific training exercise, or a series of dives conducted within a specific course of instruction, such as a combat swimmer course. Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. 1. Ensure all preventive maintenance for each listed UBA is current. 2. Ensure all premission checkout procedures are accomplished for each listed UBA (Table 2-4). 3. Record mission UBA serial numbers below: CAUTION All preventive maintenance is current and all premission checkout procedures have been accomplished for each listed UBA. Date MK 25 UBA Technician Figure 2-3. Ready for Issue (RFI) Log. REVISION

38 MAINTENANCE REQUIREMENTS 1. Inspect and clean recirculation subsystem. 2. Inspect pneumatic subsystem. 3. Inspect equipment housing and harnesses. Table 2-4. Premission Checkout Procedures. MATERIALS, PARTS, TOOLS, AND TEST EQUIPMENT MATERIALS 1. [01550] Grease, aircraft and instrument, MIL-PRF-27617, Type III, Hazardous Material User s Guide, Group 8, Disposal Method 1 2. [00294] Cloths, cleaning TOOLS 1. Screwdriver, 5.5 mm, PN , CAGE Wrench, open-end, 5.5 mm, PN , CAGE O-ring removal pick, PN , CAGE MISCELLANEOUS 1. Table Table Figure 7-2A 4. Figure 7-2B 5. Figure Figure Figure 7-10A 8. Figure 7-11A 9. Figure 7-11B NOTE 1: Numbers in brackets can be referenced to Standard PMS Materials Identification Guide (SPMIG) for stock number identification. CAUTION Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. NOTE 2: Accomplish this procedure as directed by Diving Supervisor or as required. NOTE 3: In conjunction with these procedures, also inspect MK 25 Mod 2 UBA cylinder and valve assemblies for damage, damaged threads, dirt and contamination. PROCEDURE 1. Inspect and clean recirculation subsystem. a. Inspect breathing bag (Figure 7-10A). (1) Inspect breathing bag seams for separation. (2) Inspect connecting pieces for corrosion or damage to threads or mating surfaces. Inspect safety cord for damage REVISION 1

39 Table 2-4. Premission Checkout Procedures Continued. 1. Inspect and clean recirculation subsystem Continued. (3) Inspect connecting piece joints. Ensure connecting pieces are secure in the breathing bag. Remove hose piece on each connecting piece and inspect whipping thread for damage or looseness. Ensure a tight seal exists between connecting pieces and breathing bag connector mounts. Inspect safety cord D-rings for rust and tabs for material tears or broken stitches. b. Inspect scrubber canister (Figure 7-8). (1) Inspect canister insulator (if applicable). (2) Inspect inside canister housing for moisture and/or carbon dioxide absorbent build up. Inspect canister housing rim for nicks and rough edges. (3) Inspect canister bayonet ports and spirawaves for damage and worn parts. (4) Remove cover seal (5) from lid and inspect for cuts, abrasions, or deterioration, especially along inside of seal. (5) Inspect lid (6) for nicks and damage, especially on the top sealing surface. Ensure lid pins (7) are intact. Refer to Table Inspect canister shaft (11) for smooth function. Reinstall cover seal. Do not lubricate. (6) Inspect screen/spring assembly (8) for damage or absorbent build-up. (7) If necessary, clean canister screens and canister rod (see Table 6-12 for Mod 2 [urethane] canister and Table 4-3). When completely dry, loosely connect canister lid to canister housing until ready for use. c. Inspect breathing hoses and mouthpiece (Figure 7-9). (1) Gently stretch each hose and inspect for damage. Inspect exhalation and inhalation hose one-way valves (discs) for proper operation, deterioration, and missing parts. (2) Inspect mouthpiece valve for cleanliness and presence of foreign matter. Ensure rotary valve is operational. (3) If necessary, clean and/or sanitize breathing bag, hoses, and/or mouthpiece in accordance with Table 4-3. WARNING Different brands of MIL-PRF-27617, Type III, greases should never be mixed. Ensure all old grease is removed prior to applying new grease. d. Remove all O-rings on breathing bag, exhalation hose, and inhalation hose. Ensure all old grease is removed from O-rings and O-ring grooves. Lightly lubricate O-rings and reinstall. 2. Inspect pneumatic subsystem. a. Inspect oxygen reducer (Figures 7-2A and 7-2B). (1) Remove reducer plug and inspect reducer high-pressure inlet port for oil, grease, dirt or other foreign matter. Inspect port for corrosion and damage. Inspect high-pressure inlet port O-ring for damage or deterioration. Do not lubricate. (2) Reinstall reducer plug. (3) For Model 2A reducer only: Inspect outer diaphragm for cuts, punctures, and deterioration. b. Inspect pressure lines for kinks and misaligned or loose connections. c. Inspect standard pressure gauge and gauge boot for proper alignment and damage. Ensure blow out hole is clear. - OR - Inspect flexible gauge line and gauge for damage or kinks in line. d. Inspect demand valve assembly for corrosion or contamination, misalignment with equipment housing and improper connection. REVISION

40 Table 2-4. Premission Checkout Procedures Continued. 3. Inspect equipment housing and harnesses (Figures 7-11A and 7-11B). a. Inspect interior and exterior of equipment housing for damage. Inspect slotted indents for sharp edges that could cause cuts to breathing hoses. b. Inspect lead shot pouch assembly (at demand valve) and shot pouches for damage. c. Inspect cylinder and canister straps and UBA harnesses for wear, missing parts, or other damage. d. If cord clips are used, ensure both cord clips are present, in good condition, and are installed onto cylinder straps correctly. e. Inspect all screws and cable ties for tightness. Inspect reducer holder for corrosion or damage REVISION 1

41 MK 25 MOD 2 UBA PREDIVE CHECKLIST DIVER NAME RATE DATE RIG# O 2 PRESSURE BAR or PSIG CO 2 ABSORBENT LOCATION WATER TEMP CAUTION Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. This checklist is a recommended flow only. Steps may be rearranged at the Command s discretion as long as all steps are performed. Inspect all components for dirt, deterioration, damage, or residual water during initial setup. Also, check all O-rings for damage and proper lubrication. Refer to the MK 25 Mod 2 Underwater Breathing Apparatus (UBA) Operation and Maintenance Manual, NAVSEA SS600-A3-MMA-010/53833, for detailed step-by-step procedures. DIVER INITIALS INITIAL SETUP STEPS (Table 2-5) 1. Diving Supervisor verifies UBA on RFI Log and initials this step. 2. Ensure oxygen cylinder is charged. If applicable, refer to Table 2-5, step Fill soda lime canister in accordance with Table 2-5, step 3.a 3.e. 3f. Diving Supervisor verifies canister is properly filled and initials this step. 3g. Complete assembly of soda lime canister in accordance with Table 2-5, step 3.g. 4. If applicable, prepare UBA for cold-water use. 5. Inspect one-way valves and attach hoses to mouthpiece. 6. Check operation of one-way valves in hoses; close mouthpiece rotary valve. 7. Inspect breathing bag. 8. Assemble/install breathing bag and canister. 9. Attach exhalation hose to canister. 10. Attach inhalation hose to breathing bag. 11. Inspect hose slots and install inhalation and exhalation hoses in equipment housing. 12. Gauge oxygen cylinder pressure and record at top of checklist. 13. Complete UBA assembly. Check breathing bag safety cord for lateral movement. 14. Empty breathing bag. Observe breathing bag for two minutes. Breathing bag must remain depleted. 15. Diving Supervisor checks previous steps, initials this step, and records deficiencies below. Figure 2-4. Predive Checklist (Sheet 1 of 2). REVISION

42 PREDIVE CHECKOUT (Table 2-6) Open cylinder valve; record oxygen cylinder pressure: bar or psig (must be ±10 bar or ± psig of step 12). Depress bypass knob until breathing bag is full. Do not overfill. (6 to 8 seconds [maximum seconds] to fill). With mouthpiece rotary valve closed (surface position), immerse rig in water; check for leaks; remove rig from water. Shut cylinder valve; open mouthpiece rotary valve; vent system; 3. deplete breathing bag; close mouthpiece rotary valve. 4. Diving Supervisor checks previous steps, initials this step, and records deficiencies below. 5. Diver and Diving Supervisor sign checklist. 6. Stow UBA, if applicable. Refer to Table 2-6, step 6. Stow this predive checklist with UBA. REMARKS: (Note deficiencies) DIVER SIGNATURE DIVING SUPERVISOR SIGNATURE Figure 2-4. Predive Checklist (Sheet 2 of 2) REVISION 1

43 1. Initiate checklist. Table 2-5. Initial Setup Procedures. a. Diving Supervisor verifies UBA serial numbers on RFI Log (Figure 2-3). b. Initiate Predive Checklist (Figure 2-4). c. During initial setup, inspect all components for dirt, deterioration, damage, or residual water. Check all O-rings for damage and proper lubrication. 2. Fill oxygen cylinder. CAUTION Do not allow oil, grease, or any other foreign material to come in contact with high-pressure oxygen. Such material exposed to oxygen under high-pressure may explode or ignite, causing diver injury or death. Keep sparks and flames away from oxygen systems. Secure electrical equipment in immediate area during maintenance of oxygen systems. Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. NOTE The aviator's oxygen used shall be in accordance with Performance Specification MIL-PRF a. Install filling adapter (PN ) to high-pressure oxygen source line and purge high-pressure filling line of gas and particles by briefly opening high-pressure oxygen source. b. Attach oxygen source line with filling adapter to cylinder valve. c. Fully open cylinder valve. WARNING Empty oxygen cylinders may contain residual nitrogen. Ensure empty oxygen cylinders are properly purged prior to fill. Failure to comply can cause diver injury or death. Do not exceed fill rate of 200 psig (14 bar) per minute and do not charge oxygen cylinder above 3,000 psig (207 bar). Damage to cylinder can occur and can cause diver injury or death. NOTE It is normal for the oxygen cylinder to become warm during charging. d. Slowly open stop valve for high-pressure oxygen source. Purge empty oxygen cylinder by pressurizing with oxygen to psig. e. Relieve pressure, then purge again. f. Fill oxygen cylinder to desired pressure, taking at least one minute per 200 psig (14 bar). g. Shut cylinder valve; shut stop valve for oxygen source. REVISION

44 2. Fill oxygen cylinder Continued. Table 2-5. Initial Setup Procedures Continued. h. Bleed pressure from charging line; disconnect cylinder valve from charging line. i. Assemble cylinder pressure test assembly (PN ) to cylinder valve; ensure test assembly bleed valve is fully shut. j. Slowly open cylinder valve and observe test assembly gauge. Correct pressure indication is 3,000 psig (207 bar) for a completely filled cylinder; however, Diving Supervisor may justify lower pressure depending on mission profile. k. Shut cylinder valve; bleed pressure from test assembly; disconnect test assembly from cylinder valve. Install cylinder valve cap. 3. Fill soda lime canister. WARNING Do not use 8-12 mesh absorbent in the Mod 0 (fiberglass) scrubber canister. The internal design of this canister allows the smaller size absorbent to migrate past the upper screen, which may cause diver injury if inhaled. Do not mix different brands of absorbent in the same canister. Granules could pulverize and lead to channeling of the absorbent, causing diver injury or death. Contact with carbon dioxide absorbent dust will irritate the eyes, throat, and skin. Take appropriate precautions to avoid breathing absorbent dust or getting it into your eyes or on your skin. Do not stand downwind of canister while filling or emptying. Diver injury can occur. Thoroughly settle bed of carbon dioxide absorbent granules. If improperly filled, channels which permit gas to bypass the absorbent may form, causing elevated levels of carbon dioxide in the breathing loop. Diver injury or death can occur. Do not use last 1-inch of carbon dioxide absorbent in container because absorbent dust accumulates at bottom of container. Dust contributes to channeling of the absorbent, which may cause diver injury or death. NOTE When filling soda lime canister, it is advisable to hold absorbent container approximately 24 inches above scrubber canister and fan the granules while they are falling to remove most small absorbent dust particles. Canister will hold pounds of absorbent. a. Ensure interior of canister housing is clean and dry. b. Fill canister with absorbent to 1/3 level and lightly tap sides (shake down) to settle absorbent. Tap one side of canister and then the other side REVISION 1

45 3. Fill soda lime canister Continued. Table 2-5. Initial Setup Procedures Continued. WARNING Do not overfill canister. Overfilling can lead to canister flooding, which may cause diver injury or death. For Mod 2 (urethane) scrubber canister, correct fill is 1/8" to 1/4" below bottommost scribe line. c. Fill to 2/3 level and shake down; continue filling and shaking down until absorbent is at "FULL" mark. For Mod 2 (urethane) canister only: fill to 1/8" to 1/4" below bottommost scribe line. d. When filling is completed, inspect threads of canister rod for absorbent. Remove all absorbent from threads of canister rod. An "AP" brush or toothbrush may be used to remove absorbent from threads. e. Inspect canister intake and outlet ports for spillover of absorbent granules. Remove all absorbent from port area and wipe clean; wipe canister seal lip clean of dust before installing canister lid. f. Diving Supervisor verifies canister is properly filled and initials Predive Checklist. CAUTION Do not over-tighten canister lid. Over-tightening the canister lid to canister housing will damage the canister lid seal. g. Install lid and finger tighten canister pin. Ensure canister lid seal is seated properly. Ensure canister pin and rod are not cross threaded. 4. If applicable, prepare UBA for cold-water use. NOTE Operational requirements determine the necessity of canister insulator (see paragraph 2.1.4). Use of canister insulator may cause condensation to collect in the breathing bag or diaphragm chamber of the demand valve, causing a gurgling sound when using the UBA. Be familiar with all symptoms of system flooding. a. Place canister into larger insulator. Canister lid will be visible. Align holes of insulator with ports on canister. Close Velcro loop over canister lid. b. Place smaller insulator fully over lid and align hole with inlet port of canister. NOTE If the canister insulator is used, lead shot pockets and pouches must be fitted at the demand valve. c. If required, install lead shot pouch pockets under demand valve. (1) With pin spanner wrench, remove demand valve threaded ring. (2) Push demand valve through hole in equipment housing. (3) Fit pocket assembly around demand valve screw cap. Pocket flaps open towards the reducer end of the UBA. (4) Reinstall demand valve within hole in equipment housing; reinstall threaded ring. d. If canister insulator package is used, inspect lead shot pouches and pockets for torn seams or ripped fabric. e. Ensure lead shot does not leak from pouches. REVISION

46 Table 2-5. Initial Setup Procedures Continued. 4. If applicable, prepare UBA for cold-water use Continued. NOTE Standing the UBA on the gauge end may facilitate fitting the lead shot pouch into the pockets at the demand valve. f. Install one lead shot pouch into each of the two pockets at the demand valve. 5. Inspect one-way valves and attach hoses to mouthpiece. a. Ensure all breathing hose O-rings are properly lubricated. b. Inspect one-way valves and attach inhalation and exhalation hoses to mouthpiece in accordance with color code: red dot for exhalation; no color marking for inhalation. c. Ensure one-way valve end of each hose is connected to mouthpiece. Red inner ring indicates exhalation hose. 6. Check operation of one-way valves and close mouthpiece rotary valve. WARNING Check the one-way valves in both hoses prior to each operation. Failure to comply can cause diver injury or death. NOTE When blowing through hose in the direction of flow, ensure valves open easily. When pulling gas against flow direction, ensure valves close tightly. a. Inspect and check operation of one-way valves (check valves) in inhalation and exhalation hoses. Place mouthpiece rotary valve in dive position; place mouthpiece in mouth. Crimp inhalation hose with hand and inhale. No gas flow allowed. Remove hand from hose and inhale. Gas should flow freely. Crimp exhalation hose with hand and exhale. No gas flow allowed. Remove hand from hose and exhale. Gas should flow freely. b. Place mouthpiece rotary valve in surface position. 7. Inspect breathing bag. CAUTION When inspecting breathing bag connecting pieces for secure attachment, do not use fingernails to pry connecting pieces from breathing bag. a. Inspect breathing bag for residual water inside. Drain if necessary. b. Inspect breathing bag connecting pieces to ensure they are fully attached to breathing bag. c. Ensure breathing bag O-rings are properly lubricated REVISION 1

47 8. Assemble/install breathing bag and canister. Table 2-5. Initial Setup Procedures Continued. NOTE The breathing bag and canister may be assembled and installed using Option I or Option II. If canister insulator is used, ensure insulator material is not pinched between canister port and bayonet connecting pieces of breathing bag and exhalation hose. OPTION I a. Attach bayonet connecting piece on breathing bag to canister outlet port. The canister outlet port (to breathing bag) is the port closest to the bottom of the canister. NOTE If breathing bag is improperly installed, the demand valve connecting piece will point upward when canister is placed in equipment housing. Remove breathing bag and reinstall so that demand valve connecting piece points downward. b. Rotate connecting piece 90 degrees to lock. c. Place canister in housing with canister lid to the left. CAUTION Threaded connecting piece on breathing bag is plastic and demand valve is metal. Attach breathing bag to demand valve with care; connecting piece cap nut can be easily cross threaded. d. Grasp breathing bag/demand valve connecting piece and insert into demand valve; thread connecting piece cap nut carefully onto demand valve. e. Proceed to step 9. OPTION II CAUTION Threaded connecting piece on breathing bag is plastic and demand valve is metal. Attach breathing bag to demand valve with care; connecting piece cap nut can be easily cross threaded. a. Grasp breathing bag/demand valve connecting piece and insert into demand valve; thread connecting piece cap nut carefully onto demand valve. b. Fold breathing bag up. Place canister upright (lid up) in equipment housing. The canister outlet port (to breathing bag) will be closest to the bottom. NOTE Ensure breathing bag is not twisted after connection is made. c. Attach bayonet connecting piece on breathing bag to canister outlet port; hold breathing bag connecting piece while rotating canister 90 degrees to lock connecting piece (laying canister into housing). REVISION

48 9. Attach exhalation hose to canister. Table 2-5. Initial Setup Procedures Continued. a. Attach exhalation hose bayonet connecting piece to canister intake port. b. Rotate connecting piece 90 degrees to lock. c. Lay canister flat in equipment housing. Feed cylinder/canister strap over canister or secure two Velcro tabs around canister. 10. Attach inhalation hose to breathing bag. Attach inhalation hose to breathing bag by pulling out muff on breathing bag and hand tighten hose connection as shown in Figure 2-5. Reinsert muff when hose is secured. 11. Inspect hose slots and install inhalation and exhalation hoses in equipment housing. a. Inspect hose slots in equipment housing for good condition. b. Carefully position inhalation and exhalation hoses in respective slots. c. Ensure hoses are not twisted. 12. Gauge cylinder pressure and record at top of checklist. a. Remove cylinder valve cap from cylinder valve. b. Gauge oxygen cylinder pressure and record on Predive Checklist (Figure 2-4). 13. Complete UBA assembly and check breathing bag safety cord for lateral movement. a. Remove reducer plug and position oxygen cylinder. b. If cord clips are not installed, position breathing bag safety cord in position loosely between oxygen cylinder and equipment housing. Tighten cylinder positioning strap (leftmost cylinder strap). c. Attach cylinder valve to oxygen reducer. d. Attach cylinder/canister strap (or tighten second cylinder strap). Ensure positioning strap is tightened. e. If using cord clips, secure breathing bag safety cord to cord clips. f. Check safety cord to ensure that it is not binding and has lateral movement under the cylinder straps. 14. Empty breathing bag and observe breathing bag for two minutes. a. Ensure that cylinder valve is shut. b. Open mouthpiece rotary valve (set on dive position). While inhaling through mouthpiece and exhaling through nose, exhaust all gas from breathing bag until bag is completely collapsed; close mouthpiece rotary valve (surface position). The valve is closed when in down position. c. Observe breathing bag for 2 minutes. During this period, bag must remain completely collapsed. If bag takes in any air, proceed in accordance with troubleshooting section in Chapter Diving supervisor checks previous steps, initials, and records deficiencies. a. Diving Supervisor checks previous steps to verify proper completion. b. Record any deficiencies on Predive Checklist (Figure 2-4) REVISION 1

49 Table 2-5. Initial Setup Procedures Continued. Figure 2-5. Attachment of Inhalation Hose to Breathing Bag Model 2A. REVISION

50 1. Check and record oxygen cylinder pressure. Table 2-6. Predive Checkout Procedures. a. Fully open oxygen cylinder valve and then close valve one-quarter turn to prevent valve from jamming open. Automatic demand valve should activate. b. Ensure cylinder pressure is adequate for the mission, as dictated by the Diving Supervisor. (Check UBA pressure gauge.) The pressure reading should be within ±10 bar or ±145 psig of reading taken in Step 12 of Table 2-5. c. Record cylinder pressure on Predive Checklist (Figure 2-4). CAUTION Do not overcharge the breathing bag since damage to the system may occur. Breathing bag should be firm, but not stretched. 2. Check time required to fill breathing bag. a. With mouthpiece rotary valve still closed, test demand valve by depressing bypass knob on front of housing. b. Note time required to fill breathing bag. Breathing bag filling time should be approximately 6 to 8 seconds and should not exceed 12 seconds. If filling time exceeds 12 seconds, proceed in accordance with troubleshooting procedure in Chapter Check for leaks. a. With mouthpiece rotary valve still closed (surface position), immerse the entire UBA in dip tank. b. Remove any surface gas bubbles remaining from initial immersion and observe for leaks. If applicable, lift canister insulator lid to allow any trapped air to escape from insulation. Observe lid of canister carefully for leaks. There should be no bubbles rising because of gas leakage. If leaks are observed, perform troubleshooting procedures in Chapter 5. c. Remove UBA from dip tank. d. Open mouthpiece rotary valve; shut cylinder valve. Vent pneumatic subsystem. Deplete breathing bag and close mouthpiece rotary valve (surface position). 4. Diving Supervisor check previous steps, initials, and records deficiencies. a. Diving Supervisor checks and initial previous steps to verify proper completion. b. Record any deficiencies on Predive Checklist (Figure 2-4). 5. Diver and Diving Supervisor sign predive checklist. a. Diver and Diving Supervisor sign Predive Checklist (Figure 2-4), affirming that the initial setup and the predive checkout procedures have been performed. NOTE If using 4-8 mesh carbon dioxide absorbent, the MK 25 Mod 2 UBA may be stowed for up to 14 days before use. Follow Steps 6.a through 6.d. Do not stow if using 8-12 mesh absorbent. 6. Stow UBA and predive checklist, if applicable. a. Ensure breathing bag is depleted and mouthpiece rotary valve is in the closed (surface) position. b. Ensure oxygen cylinder valve is shut. c. Place a copy of completed Predive Checklist (Figure 2-4) with the MK 25 Mod 2 UBA. d. 4-8 mesh absorbent only: Stow the MK 25 Mod 2 UBA for a period not to exceed 14 days prior to use REVISION 1

51 Table 2-7A. Purge Procedure Decision Tree. WARNING Ensure proper purge procedures are completed. Failure to comply can cause diver injury or death. Before proceeding, read and understand the purpose and precautions of the purge procedures, paragraph and subparagraphs through If the purge procedure is interrupted at any point, the procedure should be repeated. It should also be repeated any time the mouthpiece is removed and air is breathed. Additional purging during the dive is not necessary and should not be performed unless mouthpiece has been removed and air has been breathed. Use the flowchart below to determine which purge procedure is applicable to the dive. Ensure proper UBA donning is accomplished. YES Is the MK 25 Mod 2 UBA the only UBA used during this particular drive? NO Use Table 2-7B, Predive/Surface Transit Purge Procedure. NOTE Are multiple breathing sources used with the SDV? YES See Appendix A For emergency descent prior to proper purge procedure, use Table 2-7C, Emergency Descent Purge Procedure. NO Stop Stop Use Table 2-7D, Underwater Purge Procedure. Ensure Surface Phase is performed prior to Pressurized Phase. Stop Ensure proper UBA donning. a. Attach UBA harnesses so that the breathing bag is in the same relative position as the lungs (top of UBA should be 7 to 10 inches below the chin). b. Ensure UBA harnesses fit loosely enough to permit complete filling of the breathing bag. There should be a distance of one closed fist between the bag and the diver's chest. c. To prevent nitrogen from entering the breathing loop, ensure the facemask creates an airtight seal to the face. REVISION

52 Table 2-7B. Predive/Surface Transit Purge Procedure. Use this procedure if the MK 25 Mod 2 UBA is the only UBA used during the dive. Perform the procedure immediately before submerging (either on predive or after a surface transit). CAUTION Be familiar with the procedures in Table 2-7C, Emergency Descent Purge Procedure. NOTE Ensure proper donning of UBA is accomplished (Table 2-7A). 1. Insert mouthpiece. a. Ensure that oxygen cylinder valve is shut. With the mouthpiece in the closed (surface) position, exhale completely into the mouthpiece to clear the mouthpiece. b. Open mouthpiece rotary valve (dive position). The rotary valve is left open for the remainder of the procedure. 2. Empty breathing bag. If breathing bag is partially filled, empty bag by inhaling through the mouthpiece and exhaling through the nose until bag is completely empty. 3. Fill breathing bag completely. a. Open oxygen cylinder valve. Demand valve will activate. b. Fill breathing bag completely by depressing bypass knob for 6-8 seconds, or until bag begins to press against diver's chest. CAUTION Do not exhale into the mouthpiece during the emptying process in Step Empty breathing bag. a. Empty breathing bag by inhaling from mouthpiece and exhaling to the atmosphere (through the nose). b. Continue until bag is completely empty and demand valve activates. 5. Refill breathing bag to comfortable volume. Fill breathing bag to a comfortable volume for swimming by depressing bypass knob completely for approximately 4 seconds. Begin normal breathing on the UBA REVISION 1

53 Table 2-7C. Emergency Descent Purge Procedure. Use this procedure if the MK 25 Mod 2 UBA is the only UBA used during the dive and an emergency descent prevents proper surface purge procedure from being completed. CAUTION Ensure MK 25 Mod 2 UBA oxygen cylinder valve is open before descending. 1. Open cylinder valve, clear mouthpiece and descend. a. Open MK 25 Mod 2 UBA oxygen cylinder valve. The valve is left open for the remainder of the procedure. b. With the MK 25 Mod 2 UBA mouthpiece in the closed (surface) position, exhale completely into the mouthpiece to clear the mouthpiece. c. Open mouthpiece rotary valve (dive position) and make emergency descent. d. Add oxygen during descent by depressing the demand valve bypass knob. Perform the purge immediately upon reaching depth. Failure to comply can cause diver injury or death. 2. Empty breathing bag. a. At depth, breathe down breathing bag by inhaling from the mouthpiece and exhaling through the nose. b. Continue until bag is completely empty and demand valve activates. c. Clear standard facemask if necessary. 3. Fill breathing bag completely. WARNING Completely fill breathing bag by depressing bypass knob for 6-9 seconds, or until bag begins to press on diver's chest. CAUTION Do not exhale into the mouthpiece during the emptying process in Step Empty breathing bag. a. Empty breathing bag by inhaling from mouthpiece and exhaling through the nose. b. Continue until bag is completely empty and demand valve activates. 5. Refill breathing bag to comfortable volume. Fill breathing bag to a comfortable volume for swimming by depressing bypass knob until bag holds enough gas for one full breath. Begin normal breathing on the UBA. REVISION

54 Table 2-7D. Underwater Purge Procedures (Other than SDV Scenarios). Use this procedure if the dive was begun on another UBA that uses a breathing gas other than oxygen and the diver will begin breathing from the MK 25 Mod 2 UBA while at increased pressures less than 30 fsw. For SDV switchover purge procedures, see Appendix A. CAUTION This procedure is not approved for depths deeper than 30 fsw. This procedure consists of a Surface Phase and a Pressurized Phase; both phases must be accomplished to ensure safe purging. The Surface Phase must be performed prior to the Pressurized Phase. NOTE Ensure proper UBA donning is accomplished (Table 2-7A). SURFACE PHASE 1. Insert mouthpiece. a. Ensure that oxygen cylinder valve is shut. Exhale completely and insert mouthpiece. b. Open mouthpiece rotary valve (dive position). 2. Empty breathing bag. If the breathing bag is partially filled, empty bag by inhaling through the mouthpiece and exhaling through the nose until bag is completely empty. 3. Fill breathing bag completely. a. Open oxygen cylinder valve. Demand valve will activate. b. Fill breathing bag completely by depressing bypass knob for 6-8 seconds, or until bag begins to press against diver's chest. CAUTION Do not exhale into the mouthpiece during the emptying process in Step Empty breathing bag. a. Empty breathing bag by inhaling from mouthpiece and exhaling to the atmosphere (through the nose). b. Continue until bag is completely empty and demand valve activates. 5. Refill breathing bag and secure UBA. a. Fill breathing bag one-half full by depressing bypass knob completely for approximately 4 seconds. b. Place rotary valve in closed ( surface) position. c. Shut oxygen cylinder valve REVISION 1

55 Table 2-7D. Underwater Purge Procedures (Other than SDV Scenarios) Continued. PRESSURIZED PHASE CAUTION Ensure Surface Phase has been completed prior to beginning Pressurized Phase. Ensure MK 25 Mod 2 UBA oxygen cylinder valve is open before discontinuing breathing on other UBA. 1. Prepare MK 25 Mod 2 UBA. a. Open MK 25 Mod 2 UBA oxygen cylinder valve. The valve is left open for the remainder of the procedure. b. Inhale and hold breath. c. Remove UBA used on initial portion of dive. Don standard facemask, if necessary. 2. Insert mouthpiece and empty breathing bag. a. With the MK 25 Mod 2 UBA mouthpiece in the closed (surface) position, exhale briefly into the mouthpiece to clear the mouthpiece. b. Open mouthpiece rotary valve (dive position). The rotary valve is left open for the remainder of the procedure. c. Exhale remaining breath into the mouthpiece and into the breathing bag. d. Breathe down breathing bag by inhaling from the mouthpiece and exhaling through the nose. e. Continue until bag is completely empty and demand valve activates. f. Clear standard facemask if necessary. 3. Fill breathing bag completely. Completely fill breathing bag by depressing bypass knob for approximately 9 seconds, or until bag begins to press on diver's chest. CAUTION Do not exhale into the mouthpiece during the emptying process in Step Empty breathing bag. a. Empty breathing bag by inhaling from mouthpiece and exhaling to the atmosphere (through the nose). b. Continue until bag is completely empty and demand valve activates. 5. Refill breathing bag to comfortable volume. Fill breathing bag to a comfortable volume for swimming by depressing bypass knob until the breathing bag contains enough gas for a full breath. Begin normal breathing on the UBA. REVISION

56 Table 2-8. Doffing Procedures. 1. Remove mouthpiece. Place mouthpiece rotary valve in the closed (surface) position and remove mouthpiece from mouth. 2. Doff the apparatus. While holding the MK 25 Mod 2 UBA, loosen or unbuckle UBA harness and remove apparatus from diver. 3. Perform postdive maintenance. Perform postdive maintenance procedures listed in Table 2-9 (summarized in Postdive Checklist, Figure 2-6) REVISION 1

57 MK 25 MOD 2 UBA POSTDIVE CHECKLIST DIVER NAME RATE DATE UBA# CAUTION For steps 1 through 5, the oxygen cylinder must remain on the UBA and the UBA must be pressurized. Failure to pressurize the UBA prior to soaking will cause flooding of the reducer. Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. NOTE For repetitive dives using the same MK 25 Mod 2 UBA, perform a complete postdive check only at the end of the dive day. The checklist below parallels the procedures in Table 2-9. DIVER INITIALS 1. Ensure mouthpiece rotary valve is in the closed (surface) position. 2. Pressurize UBA by manually activating demand valve bypass knob. 3. Thoroughly soak or rinse UBA in warm, fresh water. Remove from soak. 4. Remove breathing loop from equipment housing. 5. Repeat soak or rinse of equipment housing. Remove UBA from water. Purge demand valve of all water. 6. Shut oxygen cylinder valve and vent pneumatic subsystem. 7. Remove oxygen cylinder; insert reducer plug in reducer; place cylinder valve cap on cylinder valve. Turn in oxygen cylinder assembly for recharging. 8. Disassemble mouthpiece from hoses and the hoses from canister and breathing bag. Disassemble breathing bag from canister. Figure 2-6. Postdive Checklist (Sheet 1 of 2). REVISION

58 9. Inspect and sanitize (as needed) mouthpiece, hoses, and breathing bag. 10. Remove canister insulator (if installed); empty soda lime canister. 11. Inspect, rinse, clean, and dry and reassemble canister. 12. Ensure all components are completely dry and store. 13. Complete logs and checklist. REMARKS: (Note deficiencies) DIVER SIGNATURE DIVING SUPERVISOR SIGNATURE Figure 2-6. Postdive Checklist (Sheet 2 of 2) REVISION 1

59 Table 2-9. Postdive Maintenance Procedures. CAUTION For steps 1 through 5, the oxygen cylinder must remain on the UBA and the UBA must be pressurized. Failure to pressurize the UBA prior to soaking will cause flooding of the reducer. Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. NOTE For repetitive dives using the same MK 25 Mod 2 UBA, perform a complete postdive check only at the end of the dive day. 1. Ensure mouthpiece rotary valve is closed. a. Initiate Postdive Checklist, Figure 2-6. b. Ensure mouthpiece rotary valve is in the closed (surface) position. 2. Pressurize UBA. Pressurize UBA by manually activating the demand valve bypass knob. NOTE Soaking the MK 25 Mod 2 UBA in warm, fresh water is preferred to rinsing. Soaking removes salt deposits more completely from hidden areas of the UBA. 3. Soak or rinse UBA in warm, fresh water. a. Soaking: Immerse entire MK 25 Mod 2 UBA in warm, fresh water and allow to soak. Agitate UBA periodically. Remove UBA from water. b. Rinsing: Rinse entire UBA thoroughly with fresh water. 4. Remove breathing loop from equipment housing. a. Place mouthpiece rotary valve in open (dive) position to relieve pressure in breathing bag. Carefully remove inhalation and exhalation hoses from slotted indents. b. Open cylinder and canister straps. c. Free breathing bag safety cord from under cylinder straps or from cord clips, as applicable. d. Disconnect breathing bag from demand valve. e. Carefully remove breathing loop (mouthpiece, hoses, breathing bag, and canister) from equipment housing. f. Reattach cylinder straps. 5. Repeat soaking or rinsing of equipment housing; purge demand valve. a. With breathing loop removed and demand valve still pressurized (oxygen cylinder still attached and cylinder valve open), repeat soaking or rinsing of equipment housing, paying particular attention to the demand valve. b. On completion of soaking/rinsing, remove UBA from water. Invert equipment housing (demand valve outlet pointed down), and purge demand valve of all water. REVISION

60 Table 2-9. Postdive Maintenance Procedures - Continued. 6. Shut oxygen cylinder valve and vent pneumatic subsystem. Shut oxygen cylinder valve. Bleed down oxygen by depressing bypass knob. Slowly break connection between oxygen cylinder valve and reducer by turning reducer handwheel. 7. Remove oxygen cylinder. WARNING Failure to install cylinder valve cap and reducer plug may result in dirt and/or water entering the reducer, degrading performance of the oxygen reducer and creating the potential for an oxygen fire. a. Open cylinder straps. Remove oxygen cylinder assembly. Immediately insert reducer plug into reducer high-pressure inlet port. b. Place cylinder valve cap over cylinder valve output port. c. Turn in oxygen cylinder assembly for recharging. 8. Disassemble mouthpiece, hoses, and breathing bag. a. Disconnect exhalation hose from canister by rotating bayonet connecting piece 90 degrees until slots line up. Remove exhalation hose from canister. b. Remove inhalation hose from breathing bag. c. Disconnect both hoses from mouthpiece. d. Disconnect breathing bag from canister by rotating bayonet connecting piece 90 degrees until slots line up. Remove breathing bag from canister. 9. Inspect and sanitize (as needed) mouthpiece, hoses, and breathing bag. a. Inspect disassembled components for wear and damage. b. Sanitize breathing bag, mouthpiece, and hoses in accordance with Chapter 4, Table 4-3. WARNING 10. Empty soda lime canister. Contact with carbon dioxide absorbent dust will irritate the eyes, throat, and skin. Take appropriate precautions to avoid breathing absorbent dust or getting it into your eyes or on your skin. Do not stand downwind of canister while filling or emptying. Diver injury can occur. a. If installed, remove canister insulator package. b. Stand canister on end with lid upward and remove lid. c. Place canister lid in a container of fresh water. d. Empty canister contents (absorbent) into a specified container for disposal and note any variation in color of the absorbent or any excessive moisture content REVISION 1

61 Table 2-9. Postdive Maintenance Procedures - Continued. 11. Inspect, rinse, clean, dry, and reassemble canister. Keep the canister components separate from the other UBA components while rinsing. When mixed with water, the absorbent produces a caustic base mixture, which can damage rubber and plastic components. a. Inspect and rinse canister housing and canister lid thoroughly in fresh water. b. Inspect screens, canister rod, and nut threads for excessive absorbent build up. To remove excessive absorbent refer to Tables 6-12 and 4-3. c. After rinsing, clean and dry parts thoroughly. Store canister with lid loosely assembled to canister housing. 12. Dry and store apparatus. CAUTION CAUTION All MK 25 Mod 2 UBA components must be completely dry before storage to prevent mildew formation, bacteria growth, and material rot. a. Dry equipment housing. Inspect breathing bag and demand valve for residual moisture. NOTE The breathing bag and hoses may require 3-5 days to dry completely. b. Store MK 25 Mod 2 UBA components when they are completely dry. 13. Complete logs and checklist. a. Note any failures or discrepancies in the UBA s performance. Complete Failure Analysis Report form as applicable. b. Diver and Diving Supervisor sign Postdive Checklist (Figure 2-6) confirming that postdive procedures have been performed. REVISION /(2-38 blank)

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63 CHAPTER 3 FUNCTIONAL DESCRIPTION 3.1 INTRODUCTION. The MK 25 Mod 2 Underwater Breathing Apparatus (UBA) enables closed-circuit, 100-percent oxygen diving during Special Operation Forces and Marine Corps operations in shallow water. This chapter describes the function and interrelationship of the parts, components, and assemblies of the MK 25 Mod 2 UBA General Description. The MK 25 Mod 2 UBA is worn in front of the swimmer and is attached with two UBA harnesses. The mouthpiece is held in place with a head strap. All system components are attached to or contained in an equipment housing. The oxygen cylinder is secured in place at the bottom of the equipment housing with two straps and is connected through a cylinder valve to an oxygen reducer (first stage regulator), which reduces cylinder gas pressure to an intermediate working pressure. Gas flows from the reducer to the demand valve assembly (second stage regulator). The demand valve controls oxygen flow into a single breathing bag. The swimmer receives breathing gas on demand from the breathing bag through the inhalation hose and the mouthpiece. The mouthpiece contains a rotary valve, which, in the dive (up) position, supplies the breathing gas and, in the surface (down) position, isolates the gas flow loop from the ambient atmosphere or water conditions. The exhalation hose also connects to the mouthpiece and takes exhaled gas to the soda lime canister (carbon dioxide scrubber). Both the inhalation and exhalation hoses are fitted with one-way valves (discs) to ensure the correct flow path of the gas. The canister contains a soda lime material (hydroxide chemical), which absorbs carbon dioxide. Gas flows from the canister to the breathing bag, completing the loop. Additional oxygen is metered into the breathing bag from the oxygen cylinder by the demand valve assembly as required. A pressure gauge indicates the amount of oxygen remaining in the oxygen cylinder. On the front of the equipment housing is a bypass knob, which permits the operator to bypass the (automatic) demand valve and manually add oxygen to the breathing bag Component Alternatives. The MK 25 Mod 2 UBA includes three major subsystems with principal components contained in each. The pneumatic subsystem includes the oxygen cylinder and cylinder valve, the oxygen reducer, the demand valve assembly, the pressure gauge, and the pressure lines that connect all these components. The recirculation subsystem includes the breathing bag, the carbon dioxide scrubber, the mouthpiece assembly, and the inhalation and exhalation hoses. The remaining subsystem is the equipment housing and its straps and harnesses. In recent years, more reliable and less expensive alternatives for some of these principal components have been introduced. Although the alternatives may look and be operated differently from their counterparts, the basic operation of the MK 25 Mod 2 UBA, regardless of which combination of principal components is used, does not change. REVISION 1 3-1

64 The following list shows which principal components have alternatives. The remainder of this chapter will describe these components. Principal Components Pneumatic Subsystem Oxygen Reducer (First Stage Regulator) Model 2A (original) Model 2B (new) Pressure Gauge Line Standard (hard pipe) Flexible gauge line (for use on oxygen reducer Model 2B only) Pressure Gauge Standard (top of equipment housing) Flexible (for use on oxygen reducer Model 2B only) Recirculation Subsystem Breathing Bag Model 2A (red) Carbon Dioxide Scrubber Canister Mod 0 (fiberglass, no longer manufactured) Mod 2 (urethane) Equipment Housing Subsystem Fiberglass (original, as found on converted MK 25 Mod 2) Urethane (new, as found on production MK 25 Mod 2US) Component Function and Location. Figure 3-1 shows major components of the recirculation and pneumatic subsystems and diagrams the flow of the breathing gas. From the oxygen cylinder (14), high-pressure oxygen passes through the cylinder valve (13) to the reducer (10), where high-pressure gas is reduced to an average intermediate working pressure. The gas is then piped through the low (intermediate) pressure line (11) to the demand valve assembly (6). High-pressure gas is also piped through the high-pressure line (12) to the pressure gauge (5). On inhalation, the one-way valve (disc) (3), located in the inhalation hose (4), opens and the diver receives gas from the breathing bag (7). If not enough gas is available, the demand valve actuates due to negative pressure, adding more oxygen to the system. As the diver exhales, the exhalation one-way valve (disc) (2) opens, the inhalation one-way valve (disc) (3) closes, and the exhaled gas flows through the exhalation hose (1) to the soda lime canister (carbon dioxide scrubber) (9). The gas then filters through the soda lime canister. During descent or to purge the unit, the diver depresses the demand valve bypass knob located in the front center of the equipment housing (8) to manually add oxygen to the system. 3-2 REVISION 1

65 Figure 3-1. Recirculation and Pneumatic Component Locations (As Worn). 3.2 PRINCIPAL COMPONENTS DESCRIPTION. The MK 25 Mod 2 UBA includes three major subsystems: the pneumatic subsystem, the recirculation subsystem, and the equipment housing subsystem. Each principal component is described in the following paragraphs Pneumatic Subsystem. The MK 25 Mod 2 UBA pneumatic subsystem consists of the oxygen cylinder and cylinder valve, oxygen reducer, demand valve assembly, pressure gauge, and pressure lines. Except for the pressure gauge, every time a principal component is disassembled, the parts must be cleaned using NAVSEA approved oxygen safe cleaning procedures prior to reassembly (see Table 4-3). Also, any entry into the oxygen boundary, except when removing the cylinder assembly from the reducer, requires that Reentry Control (REC) procedures be followed to maintain system certification (see Chapter 4). REVISION 1 3-3

66 Oxygen Cylinder. Cylinder Technical Specifications Material Aluminum alloy 6061-T6 (DOT 3AL) Floodable volume cubic feet (1.9 liters) Fill pressure 3,000 psig (207 bar) Capacity cubic feet (410 liters) Valve Technical Specifications Service pressure 3,000 psig Outlet connection CGA 540 (oxygen) Burst disc 5,000 psig nominal The MK 25 Mod 2 UBA oxygen cylinder is fabricated to Department of Transportation (DOT) 3AL specifications. It has internal straight threads to accept the cylinder valve. The cylinder valve outlet connection is a Compressed Gas Association (CGA) 540 connection that assembles directly to the reducer. In accordance with DOT specifications, the cylinder valve is equipped with a burst disc to eliminate dangerous over pressurization of the cylinder. Connection seal: Cylinder valve to cylinder O-ring Maintenance: In accordance with DOT guidelines, the cylinder must be internally visually inspected every year, and must undergo hydrostatic testing every 5 years. The cylinder valve must be overhauled every 5 years. 3-4 REVISION 1

67 Oxygen Reducer Model 2A. Technical Specifications Intermediate pressure setting using 100±5 bar inlet pressure psig ( bar) Adjustable Safety relief valve setting Opens psig (9-13 bar) Seats by 116 psig (8 bar) Adjustable Reducer operating range (cylinder pressure) 145-3,000 psig ( bar) The oxygen reducer is the first stage regulator on the MK 25 Mod 2 UBA. Oxygen reducer Model 2A reduces high-pressure oxygen to an intermediate working pressure of approximately 50 psig. High-pressure oxygen enters the inlet port from the cylinder valve, and is piped directly to the pressure gauge through the pressure gauge line. Intermediate pressure oxygen from the reducer s upper chamber is piped via the low-pressure line to the demand valve. Oxygen reducer Model 2A contains two safety features. First, the velocity reducer located in the high-pressure inlet port slows the high flow rate of incoming oxygen. The second safety feature is the safety relief valve, which eliminates dangerous overpressurization of the oxygen reducer in the event of a high-pressure oxygen leak. Oxygen reducer Model 2A is an "unbalanced" regulator, which means the intermediate pressure provided to the demand valve is dependent on cylinder pressure. As the cylinder pressure decreases (oxygen is used), the intermediate pressure increases. Therefore, it is imperative that the intermediate pressure setting of the reducer be set and checked using a 100±5 bar inlet source. Connection seals: High-pressure inlet port to cylinder valve O-ring High-pressure outlet port to standard pressure gauge line ridged metal sealing ring Low-pressure outlet port to low-pressure line O-ring Maintenance: The intermediate pressure output of the oxygen reducer Model 2A must be checked (and reset if necessary) annually. The reducer must be overhauled every 6 years, or when reducer flooding is suspected. During the 6-year overhaul, the safety relief valve is adjusted to its proper range. NOTE For cost savings, the oxygen reducer Model 2A may be replaced by oxygen reducer Model 2B at overhaul (see paragraph ). REVISION 1 3-5

68 Oxygen Reducer Model 2B. Technical Specifications Intermediate pressure setting using 100±5 bar inlet source psig Not adjustable Safety relief valve setting Opens psig Seats by 85 psig Not adjustable Reducer operating range (cylinder pressure) 145-3,000 psig ( bar) The oxygen reducer Model 2B is an alternative first stage regulator for the MK 25 Mod 2 UBA. Oxygen reducer Model 2B reduces high-pressure oxygen to an intermediate working pressure of approximately 65 psig. Highpressure oxygen enters the inlet port from the cylinder valve, and is piped directly to the pressure gauge through the pressure gauge line. Intermediate pressure oxygen is piped via the low-pressure line to the demand valve. Oxygen reducer Model 2B has the option of using the standard pressure gauge (located in the top of the equipment housing), or an alternative flexible gauge line and gauge (see paragraph ). If the flexible gauge is installed on the oxygen reducer Model 2B, the standard gauge and pressure gauge line must both be removed (see Table 6-13B). The oxygen reducer Model 2B contains two safety features. First, the design of the reducer housing itself deflects and slows the high flow rate of incoming oxygen. The second safety feature is the safety relief valve, which eliminates dangerous over pressurization of the oxygen reducer in the event of a high-pressure oxygen leak. Unlike the oxygen reducer Model 2A safety relief valve, the Model 2B relief valve is not adjustable. The oxygen reducer Model 2B has no over-bottom pressure compensation, which means that the reducer intermediate pressure is directly dependent on the cylinder pressure. In contrast to oxygen reducer Model 2A, as cylinder pressure decreases (oxygen is used), the pressure to the demand valve decreases. For this reason, it is imperative the intermediate pressure of the oxygen reducer Model 2B be checked using a 100±5 bar inlet source. The oxygen reducer Model 2B intermediate pressure setting cannot be adjusted. For installation of oxygen reducer Model 2B, refer to Table 6-11B. Connection seals: High-pressure inlet port to cylinder valve O-ring High-pressure outlet port to standard pressure gauge line ridged metal sealing ring High-pressure outlet port to flexible gauge line O-ring Low-pressure outlet port to low-pressure line O-ring Maintenance: The intermediate pressure output of the oxygen reducer Model 2B must be checked annually. The reducer must be overhauled every 6 years, or when reducer flooding is suspected. Neither the intermediate pressure setting nor the safety relief valve setting is adjustable. 3-6 REVISION 1

69 Demand Valve Assembly. Technical Specifications Actuation point setting with proper intermediate pressure from oxygen reducer 8.5±1.5 inches of water Manual bypass knob Allows manual addition of oxygen to breathing bag Bypass flow 60 liters per minute, minimum The demand valve assembly is the second stage regulator for the MK 25 Mod 2 UBA, and supplies oxygen to the breathing bag. The demand valve is located beneath the breathing bag, and connects to the breathing bag. It receives low (intermediate) pressure oxygen from the reducer through the low-pressure (connecting) line. As negative pressure inside the breathing bag caused by the diver s inhalation increases, the demand valve actuates, allowing oxygen into the breathing bag. As negative pressure decreases, the demand valve closes. The demand valve actuation point must be set only after verifying correct output pressure from the oxygen reducer. Depending on diving circumstances, setting the demand valve in the lower end of the range may cause it to free flow. A manual bypass knob is located on the front of the equipment housing. Depressing this knob bypasses the automatic actuation of the demand valve, allowing the diver to manually add oxygen to the breathing bag. Connection seals: Demand valve to breathing bag O-ring Maintenance: The demand valve actuation point must be checked annually after ensuring proper output pressure from the oxygen reducer. The demand valve must be overhauled every 2 years Standard Pressure Gauge. The pressure gauge, the diver's only indicator on the MK 25 Mod 2 UBA, displays oxygen cylinder pressure. The standard pressure gauge fits within a boot in the top of the equipment housing and is connected to the reducer via the standard pressure gauge line. The standard pressure gauge has a range of 0 to 350 bar (0 to 5,075 psig) and is graduated in bar; conversion to psig may be made by multiplying the gauge reading (in bar) by The standard pressure gauge and the standard pressure gauge line assembly (paragraph ), may be used with either oxygen reducer Model 2A or Model 2B. A flexible gauge line with gauge is available for the oxygen reducer Model 2B only (see paragraph ). If the flexible gauge is installed on the oxygen reducer Model 2B, the standard pressure gauge and standard pressure gauge line must both be removed. Refer to Table 6-13B. Connection seal: Standard pressure gauge to standard pressure gauge line flat metal sealing ring Maintenance: The flat sealing ring must be replaced every time the connection is broken. The gauge must be tested for accuracy every 18 months Standard Pressure Lines. Two pressure lines are used in the MK 25 Mod 2 UBA to carry oxygen. Both lines are made of chrome-plated copper tubing. The standard pressure gauge line assembly provides oxygen cylinder pressure to the standard pressure gauge from the high-pressure port of the reducer. The low-pressure (connecting) line assembly carries intermediate pressure oxygen to the demand valve from the low-pressure port of the reducer. REVISION 1 3-7

70 The standard pressure gauge line assembly and the standard pressure gauge (paragraph ) may be used with either oxygen reducer Model 2A or Model 2B. A flexible gauge line with gauge is available for the oxygen reducer Model 2B only (see paragraph ). If the flexible gauge is installed on the oxygen reducer Model 2B, the standard pressure gauge and standard pressure gauge line must both be removed. Refer to Table 6-13B. Connection seals: Standard pressure gauge line to oxygen reducer ridged metal sealing ring Standard pressure gauge line to standard pressure gauge flat metal sealing ring Low-pressure line to reducer O-ring Low-pressure line to demand valve O-ring Maintenance: The metal sealing rings must be replaced every time each connection is broken Flexible Pressure Gauge and Line. Technical Specifications For use with oxygen reducer Model 2B only Flexible high-pressure gauge line, 3,000 psig working pressure Swivel connection to reducer, sealed with O-ring Gauge range: bar (0-3,335 psig) The flexible pressure gauge line and gauge can only be installed onto the oxygen reducer Model 2B. The gauge line incorporates a swivel, which installs to the spare high-pressure (HP) port. After installation, the original HP port is capped with a second plug. The flexible pressure gauge has a range of 0 to 230 bar (0-3,335 psig) and is graduated in bar; conversion to psig may be made by multiplying the gauge reading (in bar) by If the flexible pressure gauge is installed on the oxygen reducer Model 2B, the standard pressure gauge and standard pressure gauge line must both be removed. Refer to Table 6-13B. Connection seal: Flexible pressure gauge swivel to oxygen reducer Model 2B O-ring Maintenance: The flexible gauge must be tested for accuracy every 18 months. The flexible gauge line assembly must be overhauled every 6 years in conjunction with overhaul of oxygen reducer Model 2B Recirculation Subsystem. The recirculation subsystem consists of the breathing bag, carbon dioxide scrubber canister, mouthpiece valve assembly, and inhalation and exhalation hose assemblies. During routine maintenance and performance of post-dive maintenance procedures, all components, except the soda lime canister, should be sanitized (see Chapter 4) to ensure germ-free cleanliness. 3-8 REVISION 1

71 Breathing Bag Model 2A. Technical Specifications Material Rubber coated fabric Floodable volume cubic feet (7 liters) Operational volume, approximate cubic feet (4 liters) Color Red The breathing bag Model 2A contains three connection points to other MK 25 Mod 2 UBA components. The "bayonet" fitting connects to the inhalation port of the scrubber canister. Above the bayonet, the plastic fitting with cap nut attaches to the demand valve. On the opposite side of the breathing bag from the bayonet, the plastic fitting with muff connects to the inhalation hose. The connection fittings are secured to the breathing bag Model 2A using thread and a parallel whipping knot. Inside the breathing bag, a metal spring connects the two plastic fittings. This spring prevents total collapse of the breathing bag. All of the connection fittings and the spring may be replaced as necessary. The safety cord located at the bottom of the breathing bag secures the bag to the equipment housing and prevents the inflated bag from rising up on the diver s chest. The bag acts as a flexible gas reservoir, and helps to provide underwater neutral buoyancy for the UBA. Connection seals: Bayonet fitting to scrubber canister O-ring Plastic fitting with cap nut to demand valve O-ring Maintenance: The breathing bag must be inspected for damage on predive. Both O-rings must be inspected, replaced if necessary, and properly lubricated on predive. The O-rings must be replaced every 3 years Reserved. REVISION 1 3-9

72 Soda Lime Canister (Carbon Dioxide Scrubber), Mod 2 (Urethane). Technical Specifications Material Molded urethane Floodable volume 0.09 cubic feet (2.55 liters) Absorbent weight capacity, approx pounds Cold water use Removable neoprene insulation Additional 3.18 pounds required to offset buoyancy effects Moisture trap capacity 200 cc NOTE Refer to paragraph for authorized carbon dioxide absorbents. The Mod 2 (urethane) soda lime canister removes both carbon dioxide and moisture from the gas in the breathing loop, and connects to other UBA components through two ports. The "exhalation" port is so named because it connects to the exhalation hose. It is the port closest to the canister lid. The "inhalation" port connects to the breathing bag (inhalation side of the UBA). It is the port at the bottom of the canister. The canister contains two separate chambers, the absorbent chamber and the moisture trap. Breathing gas flows from the exhalation hose through the exhalation port into the absorbent chamber where carbon dioxide gas is removed by a chemical reaction within the absorbent. Moisture is then collected in the moisture trap, which has a capacity of 200 cubic centimeters (cc). The cleaned breathing gas is delivered to the breathing bag through the inhalation port. The exhalation hose and the breathing bag connect to their respective ports using bayonet fittings. The inhalation port is slightly larger than the exhalation port, eliminating the possibility of incorrect installation. Both ports contain spirawaves (wave washers) to ensure a tight fit. The Mod 2 canister also has a removable, neoprene insulation package that should be used in colder water temperatures (less than 60 F) to maximize canister durations. If the insulation is used, an additional 3.18 pounds of weight are required on the UBA to offset the positive buoyancy effects created by the neoprene. The weights are available as two 1.59-pound lead shot pouches that fit into pockets installed around the demand valve. CAUTION Do not soak the Mod 2 (urethane) canister housing, lid, or associated soft goods in vinegar-water solution. Damage to equipment could occur. The components of the canister can be completely disassembled for cleaning. Should carbon dioxide absorbent residue clog the screens or canister rod threads, these components may be soaked in a solution of vinegar and water (Table 4-3), scrubbed lightly with a nylon bristle brush, and then rinsed with fresh water REVISION 1

73 Connection seals: Bayonet fittings (exhalation hose, breathing bag) O-rings Maintenance: The canister lid seal should be inspected on predive. Do not lubricate canister seal. The canister contains two internal O-rings that must be replaced every 3 years Soda Lime (Carbon Dioxide Scrubber) Canister, Mod 0 (Fiberglass). Technical Specifications Material Fiberglass Floodable volume cubic feet (2.5 liters) Absorbent weight capacity, approx pounds Cold water use Removable neoprene insulation Additional 3.18 pounds required to offset buoyancy effects Moisture trap capacity 200 cc NOTE Refer to paragraph for authorized carbon dioxide absorbents. As an alternative, the Mod 0 (fiberglass) soda lime canister can be used in the MK 25 Mod 2 UBA. The Mod 0 canister is no longer manufactured, but is authorized for continued use. Its function is the same as the Mod 2 (urethane) soda lime canister; however, the internal parts of this canister cannot be disassembled. The Mod 0 (fiberglass) canister uses the same neoprene insulation package as used with the Mod 2 (urethane) canister. If the insulation is used, an additional 3.18 pounds of weight are required on the UBA to offset the positive buoyancy effects created by the neoprene. The weights are available as two 1.59-pound lead shot pouches that fit into pockets installed around the demand valve. The internal components of the Mod 0 (fiberglass) canister cannot be disassembled for cleaning. However, should carbon dioxide absorbent residue clog the screens or canister rod threads, fill the canister with vinegar and water (Table 4-3) and allow to soak. Scrubbing lightly with a nylon bristle brush will help remove residue. Rinse with plenty of fresh water. Connection seals: Bayonet fittings (exhalation hose, breathing bag) O-rings Maintenance: The canister lid seal should be inspected on predive. Do not lubricate canister seal. This canister contains one internal O-ring that must be replaced every 3 years. Both the canister seal and the O-ring are interchangeable between the Mod 2 (urethane) and the Mod 0 (fiberglass) soda lime canisters Mouthpiece Valve Assembly. The mouthpiece valve assembly provides the means for passing breathing gas to and from the diver. It is secured in the diver's mouth by two rubber bite pieces and is held in place by an adjustable head strap. The mouthpiece contains the rotary valve, which opens and closes the breathing loop. The rotary valve consists of a barrel and housing. The barrels and housings are not interchangeable; each rotary valve is a matched barrel and housing set. The rotary valve is opened and closed with the rotary valve knob. Correctly installed, the knob will point downward when the rotary valve is closed and outward when the valve is open. REVISION

74 When the rotary valve is closed (down, surface position), the breathing loop is isolated from the surrounding environment. A water blowout hole, located on the bottom of the rotary valve housing, permits the diver to clear the mouthpiece of water before opening the valve. When the rotary valve is open (up, dive position), the MK 25 Mod 2 UBA is ready for breathing. The mouthpiece bite pieces are mounted onto the rotary valve housing using monofilament cord with a parallel whipping knot. The rotary valve knob contains one O-ring Inhalation and Exhalation Hoses. The corrugated inhalation and exhalation hoses are fabricated from neoprene rubber and are very flexible. The exhalation hose is longer than the inhalation hose, as the distance from the scrubber canister to the mouthpiece is longer than that from the breathing bag to the mouthpiece. The exhalation hose is easily identified by a red ring located at the mouthpiece connection of the hose. The difference in length also helps eliminate confusion on installation. The shorter inhalation hose assembly consists of the hose, one-way valve (disc), and two connecting pieces. The connecting piece with cap nut attaches to the breathing bag; the second connecting piece attaches to the mouthpiece. The two connecting pieces are different sizes, which also helps eliminate incorrect installation of the inhalation hose. The longer exhalation hose assembly consists of the hose, one-way valve (disc), and two connecting pieces. The bayonet connecting piece locks to the scrubber canister. The plastic connecting piece attaches to the mouthpiece. The plastic connecting piece on the exhalation hose is larger than the connection on the breathing bag, thereby eliminating any chance of incorrectly installing the exhalation hose to the breathing bag. Both hoses contain one-way valves (discs) at the mouthpiece end to ensure correct gas flow when the MK 25 Mod 2 UBA is used. The exhalation hose has a red ring at the mouthpiece connection which, when installed correctly, corresponds to a red dot on the mouthpiece to signify the exhalation side of the breathing loop. The inhalation side is not color coded. All four hose connecting pieces are mounted to the hoses by hose clamps. Connection seals: All four hose connections O-rings Maintenance: O-rings must be inspected on predive. Ensure O-rings are properly lubricated. All O-rings and the one-way valves must be replaced every 3 years Equipment Housing Subsystem. The equipment housing subsystem consists of the equipment housing, all required straps and harnesses, and hardware. These components need only be cleaned with soapy water when necessary REVISION 1

75 Equipment Housing (Fiberglass). Technical Specifications Material Reinforced fiberglass Straps One (1) canister/cylinder strap One (1) cylinder strap The older style, fiberglass equipment housing is fabricated as a single unit from reinforced fiberglass and provides an attachment point for all components of the MK 25 Mod 2 UBA. Slots are provided for the exhalation and inhalation hoses, oxygen reducer, and harness and strap assemblies. Circular holes are provided in the housing for the demand valve and the standard pressure gauge. The housing includes two retaining straps and two UBA harnesses. Two retaining straps are incorporated into the fiberglass housing. The cylinder/canister strap, which holds both the oxygen cylinder and canister in place, is made of 1 1/2-inch polypropylene/neoprene, elastic material. It attaches to a plate retainer located under the canister, loops over the canister, through the bottom of the housing, around the cylinder, and hooks to the bottom of the housing by means of a retaining hook. A triglide, located at the canister end of the strap, allows for adjustment. A positioning strap, made of the same elastic material, circles the oxygen cylinder and hooks to the bottom of the housing as well. This positioning strap actually secures the cylinder in place. The fiberglass equipment housing also contains two UBA harnesses used to secure the UBA to the diver. The UBA harnesses may be one of two configurations. The original harnesses are made of rubberized leather with both buckle and eyelet sections. Harness adjustment is made with slide adjusters on the eyelet sections. The newer harnesses (see paragraph ) are made of 1 1/2-inch polypropylene webbing with quick release side buckles. Harness adjustment is made with triglide adjusters. Either set of harnesses is approved for use. When properly donned, the MK 25 Mod 2 UBA fits over the lung area of the chest, with the top of the UBA 7 to 10 inches below the chin. The harnesses should fit loosely enough to allow expansion room for the breathing bag. The fiberglass equipment housing contains other necessary hardware. The equipment housing holder secures the oxygen reducer in place and is attached to the housing with two screws. Additionally, up to three sets of retaining clamps secure the pressure lines to the equipment housing. A retaining clamp set is mandatory at the bottom right of the housing to secure the pressure lines at the oxygen reducer; the other two retaining clamp sets (upper and lower left of housing) may be replaced by cable ties. REVISION

76 Equipment Housing (Urethane). Technical Specifications Material Molded urethane Straps One (1) canister/cylinder strap One (1) cylinder strap (hook section) One (1) Camlock cylinder positioning strap The newer style, urethane equipment housing is fabricated as a single unit from molded urethane. Its design is basically the same as the fiberglass equipment housing, and provides attachment points, slots, and holes for all components of the MK 25 Mod 2 UBA. The equipment housing contains three component straps and two UBA harnesses. Three component retaining straps are incorporated into the urethane housing. The cylinder/canister strap, which holds both the oxygen cylinder and canister in place, is made of 1 1/2-inch, polypropylene/neoprene, elastic material. It attaches to slots in the equipment housing located under the canister, loops over the canister, through the bottom of the housing, around the cylinder, and fastens to the hook section of the cylinder strap. The cylinder positioning strap consists of a 2-inch polypropylene strap with a Camlock locking device. Two cord clips are installed on the cylinder strap hook section and the cylinder positioning strap. The breathing bag safety cord simply loops into these cord clips, making UBA setup easier. The equipment housing also contains two UBA harnesses used to secure the UBA to the diver. The UBA harnesses may be one of two configurations. The original harnesses are made of rubberized leather with both buckle and eyelet sections (see paragraph ). Harness adjustment is made with slide adjusters on the eyelet sections. The newer harnesses are made of 1 1/2-inch polypropylene webbing with quick release side buckles. Harness adjustment is made with triglide adjusters REVISION 1

77 Either set of harnesses is approved for use. When properly donned, the MK 25 Mod 2 UBA fits over the lung area of the chest, with the top of the UBA 7 to 10 inches below the chin. The harnesses should fit loosely enough to allow expansion room for the breathing bag. The equipment housing Model 2B contains other necessary hardware. The equipment housing holder secures the reducer in place and is attached to the housing with two screws. Because of the housing design, and in contrast to the fiberglass equipment housing, only cable ties are used to secure the pressure lines to the equipment housing. REVISION /(3-16 blank)

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79 CHAPTER 4 SCHEDULED MAINTENANCE WARNING Properly performed scheduled maintenance is an essential prerequisite to safe diving operations with the MK 25 Mod 2 Underwater Breathing Apparatus (UBA). Omission or negligent performance of prescribed maintenance procedures for this equipment could result in equipment failure and possible injury or death. CAUTION Only qualified MK 25 UBA technicians shall perform maintenance on the MK 25 Mod 2 UBA; however, qualified divers may perform predive and postdive actions. 4.1 INTRODUCTION. The amount of corrective maintenance required for any equipment is determined by the quality of the scheduled maintenance performed. This chapter provides users with information to plan and schedule maintenance effectively. Included within this chapter is information concerning: a. General maintenance safety and environmental precautions b. MK 25 Mod 2 UBA Maintenance Log Reentry control procedures Failure analysis reporting Maintenance history c. Maintenance requirements: Spare parts Test equipment and tools Torque specifications Cleaning and sanitizing Lubricants O-rings and packings d. Scheduled maintenance procedures 4.2 GENERAL SAFETY AND ENVIRONMENTAL PRECAUTIONS Maintenance Safety. In addition to other safety precautions prescribed in this manual, maintenance shall be performed in accordance with the following general instructions, as appropriate. a. Keep sparks and flames away from oxygen systems. Shut down electrical equipment in immediate area during maintenance and work on oxygen systems. REVISION 1 4-1

80 b. Before working on pneumatic components, ensure that the cylinder valve on oxygen cylinder is shut and pressure is vented from pneumatic subsystem. c. Exercise extreme care when handling high-pressure cylinders. Ensure that the cylinders are adequately protected from being dropped and from other abuse that would cause structural damage or create stress risers. If a cylinder is dropped or otherwise abused, the cylinder and valve shall be inspected in accordance with Maintenance Requirement Card (MRC) A-1R Oxygen-Safe Area. Components requiring oxygen (O 2 ) related maintenance, repair, or cleaning (see Table 4-3) must be disassembled, cleaned, repaired, and reassembled in a designated "O 2 SAFE" area with the following minimum requirements: Work area must be enclosed. Work area must be free of oil and grease. Work area must be as free as possible of dust and debris. Work surface must be clean and nonporous. Personnel traffic must be restricted to the area. Work area must be well lighted. Tools shall be clean and designated for "O 2 USE ONLY." Personnel's hands, faces, and clothing shall be clean. Area shall be clearly marked: "RESTRICTED - O 2 SAFE AREA" and "NO SMOKING, EATING OR DRINKING." Hazardous Material Disposal Instructions. Each unit shall comply with its own ship/station procedures for handling disposal of hazardous materials/waste identified in the MRCs. 4.3 MK 25 MOD 2 UBA MAINTENANCE LOG. The MK 25 Mod 2 UBA Maintenance Log, also referred to as the "rig log", serves as a history of all maintenance performed on an individual UBA. Each UBA should have its own maintenance log, and should be easily identifiable. Each maintenance log shall contain the following three items, as a minimum. Reentry Control Forms (see paragraph 4.3.1) Failure Analysis Reports (see paragraph 4.3.2) Maintenance History Form (see paragraph 4.3.3) Forms shown in this manual are samples; commands are free to develop their own forms as long as all pertinent information is included on the form Reentry Control (REC) Procedures. Reentry into the MK 25 Mod 2 UBA is defined as entry into the boundaries of the oxygen subsystem of the pneumatic subsystem. Reentry includes any and all work and testing on the internal components of the oxygen subsystem. When working with high-pressure oxygen systems, such as the oxygen subsystem on the MK 25 Mod 2 UBA, accurate records must be maintained to ensure the continued integrity of the system. The Reentry Control (REC) procedures consist of recording REC data on log sheets whenever maintenance is performed, which requires entry into the REC boundaries. The REC boundaries for the MK 25 Mod 2 UBA enclose the major internal portions of the oxygen subsystem of the pneumatic subsystem. As shown in Figure 4-1, individual REC boundary connections and components are as follows: 4-2 REVISION 1

81 Connection A B C D M REC Required Yes No Yes PRESSURE GAUGE LINE (HIGH PRESSURE)/ GAUGE CONNECTION CONNECTING LINE (LOW PRESSURE)/ DEMAND VALVE CONNECTION PRESSURE GAUGE REPLACEMENT DEMAND VALVE ADJUSTMENT/REPAIR CONNECTING LINE (LOW PRESSURE) REPLACEMENT CONNECTING LINE (LOW PRESSURE)/ REGULATOR CONNECTION PRESSURE REGULATOR ADJUSTMENT/REPAIR PRESSURE GAUGE LINE (HIGH PRESSURE)/ REGULATOR CONNECTION PRESSURE GAUGE LINE (HIGH PRESSURE) REPLACEMENT REGULATOR/CYLINDER VALVE CONNECTION (NO REC ACTION REQUIRED) OXYGEN CYLINDER INSPECTION/ HYDROSTATIC TEST CYLINDER/VALVE CONNECTION CYLINDER VALVE REPAIR Figure 4-1. Reentry Control Boundaries Block Diagram. In general, the REC boundaries are all connections and component internal mechanisms that are subject to highpressure oxygen usage. The adjustments of the output pressure on the reducer and the demand valve are placed within the REC boundaries in order to regulate and document any entry into these critical adjustment areas. The connection at point C (Figure 4-1) is considered to be critical with regard to being kept oxygen clean. Because of the necessary repeated removal of the oxygen cylinder and valve assembly for routine filling, it would be impractical to observe REC procedures each time. A reducer plug and a cylinder valve cap are provided to seal both the reducer intake port and the cylinder valve port, respectively, when the connections are broken. It is imperative that these devices be used, since any foreign matter entering this area will be forced into the reducer thereby increasing the risk of a high-pressure oxygen fire and degrading reducer performance. This area shall be clean, dry, and shall not be lubricated with any compound. REVISION 1 4-3

82 REC Authorization Process. No entry into the REC boundaries shall be authorized without strict control and compliance with the following sequential procedures. Emergency and unforeseen operational circumstances may dictate a variation to this sequence. a. MK 25 UBA technician submits REC Form (Figure 4-2) to REC Supervisor. REC Forms must have detailed justification and established boundaries. b. MK 25 UBA technician and REC Supervisor meet, and REC Supervisor approves or disapproves REC action. c. REC supervisor assigns and logs (Figure 4-3) applicable REC serial number to an approved request. d. REC action is carried out and completed with supervision by REC supervisor. e. REC Form (Figure 4-2) is completed and filed in the MK 25 Mod 2 UBA log maintained for affected UBA. f. If the REC is cancelled, it is considered to be a completed action and is logged and filed in accordance with paragraph , REC Documentation Component Replacement. Replacement of components in the REC boundaries shall be as called for in the "as built" certified system. The term "as built" refers to the certified system design, specifications, parts, and operating procedures contained in this technical manual. To prevent possible contamination of other areas of the system, the open boundary ends should be sealed in double plastic bags. Following the REC actions, a demonstration of gas tightness shall be performed as follows: a. Pressurize the system with oxygen to its maximum operating pressure in accordance with the following: When testing low-pressure components (Figure 4-1; E, F, G, J, and K), a minimum of 100±5 bar (1,450 psig) must be used. However, any repair to the oxygen intake port of the reducer requires charging the UBA to its maximum operating pressure of 207 bar (3,000 psig). When testing high-pressure components (Figure 4-1; A, B, D, H, I, L, M, and repair of oxygen intake port of the reducer), the system must be charged to the maximum operating pressure of 207 bar (3,000 psig). b. Inspect all joints for leakage, using either the dip test or soap solution technique. c. For acceptance into service, no leakage shall be allowed from any component REC Documentation. a. REC documentation for the MK 25 Mod 2 UBA shall consist of the following: All reentry actions shall be documented using the REC Form (Figure 4-2). Each form shall be sequentially serialized beginning with the number 1 and progressing in ascending order without regard to date or to particular component involved. The original of each completed REC Form shall be maintained in affected UBA s maintenance log. b. A master log of all approved REC actions shall be kept in the format of the REC log sheet. c. Should additional areas of the system become accidentally contaminated during REC maintenance actions or should additional work necessitate a change to the original REC, original REC Form shall be marked as "cancelled" and a detailed explanation entered in Block 1. A cancelled REC is considered to be a completed action and is filed in accordance with step a, above. A new sheet covering the full scope of the work involved shall be submitted under a new REC serial number with reference made to the old REC Form in Block REC Responsibilities. The following division of responsibilities is suggested. Emergency and operational situations or command structure may dictate modifications. a. The Commanding Officer shall be responsible for monitoring the REC reporting procedures. 4-4 REVISION 1

83 b. Command diving officers shall be responsible for proper execution of the REC program and procedures and overall control of REC reporting procedures. c. The REC Supervisor shall be responsible for supervising all REC actions, screening and signing all forms. d. The REC supervisor shall determine if the work scope is within certification specifications and standards, assign REC Form serial numbers, and maintain appropriate records in the master log. The supervisor will supervise all work accomplished in relation to the REC maintenance action REC Forms. REC Forms, Figures 4-2 and 4-3, shall be locally reproduced as required Failure Analysis Reporting. See Chapter 6 for Failure Analysis Reporting. One copy of the Failure Analysis Report (FAR) shall be included in the affected UBA maintenance log Maintenance History Form. The Maintenance History Form provides a complete history of all maintenance that has been performed on an individual UBA. This includes not only planned maintenance and actions that require a REC Form, but also any corrective maintenance and/or actions that do not require a REC Form. The Maintenance History Form provides an easy to read list of all maintenance performed, in the chronological order in which it was performed. Figure 4-4 is a sample of the Maintenance History Form, showing pertinent information to include. REVISION 1 4-5/(4-6 blank)

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85 REENTRY CONTROL (REC) REQUEST MK 25 MOD 2 UBA ACTIVITY REC NO. DATE OPENED TECHNICIAN RIG NO. DATE CLOSED MAN HOURS 1. REC JUSTIFICATION IN DETAIL 2. ISOLATION BOUNDARIES (BY FIGURE AND INDEX NO.) 3. STEPS TAKEN TO PRECLUDE CONTAMINATION OF ANY PORTION OF SYSTEM UNAFFECTED BY REC. 4. PRESSURE TESTING REQUIREMENTS (GAS TIGHTNESS OR DIP TEST) a. GAUGE PRESSURE START FINISH b. RESULTS OF TEST 5. CLEANING PROCEDURES (IF NECESSARY) 6. ADDITIONAL COMMENTS 7. SUBMIT TO REC SUPERVISOR FOR SCREENING AND SIGNATURE MK 25 UBA Technician REC Supervisor IF APPLICABLE: REDUCER MODEL 2A or 2B (CIRCLE ONE) REDUCER SETTING PSIG (WITH COVER INSTALLED) DEMAND VALVE SETTING INCHES OF WATER -OR- PSIG (CIRCLE ONE) RELIEF VALVE SETTING: LIFTS AT PSIG RESEATS AT PSIG Figure 4-2. Reentry Control Form, MK 25 Mod 2 UBA. (Locally reproduce as required) REVISION 1 4-7

86 Instructions for REC Form REC Boundary REC Required? Min. Test Pressure (Block 4), psig A Yes 3,000 B Yes 3,000 C No - D Yes 3,000 E *Reducer HP inlet port Yes 1,450 *3,000 F Yes 1,450 G Yes 1,450 H Yes 3,000 I Yes 3,000 J Yes 1,450 K Yes 1,450 L Yes 3,000 M Yes 3,000 Preliminary. Record all identifying information at the top of the form. Each form should be sequentially serialized beginning with the number "1" and progressing in ascending order, without regard to date, component involved, or UBA involved. For "Rig No.", the serial number of the UBA is preferred. The serial number is located on a metal label attached to the equipment housing. Block 1. Provide justification for the REC Action. Cite applicable MRC(s), corrective maintenance table, etc. For corrective maintenance, provide sufficient detail of the problem that led to the corrective action. Multiple actions may be cited if applicable. For a cancelled REC: Provide justification on the REC cancellation. On new REC Form, cite cancelled REC serial number. Block 2. Identify the REC isolation boundaries (see Figure 4-1). Record the figure number (Fig. 4-1) and the letter of the boundary. Multiple letters may be cited, depending on the work involved. Block 3. Record the steps taken to protect all other components from contamination. Examples are "doublebagged connections", "work performed in oxygen safe area", etc. Block 4. Record the results of the gas tightness test performed after completing the REC action. The UBA must be pressurized to the minimum operating pressure of the component involved. See the table above for minimum charging pressures. After charging the system, perform a dip test or use leak detecting compound around all joints. Block 4a, Gauge Pressures, refers to the UBA gauge reading at the beginning of the test and at the end of the test. For acceptance back into service, no gas leakage is allowed. Block 4b, record the results of the test. "Satisfactory", etc. Block 5. Record cleaning procedures conducted, if applicable. Block 6. Record any additional information pertaining to the UBA. Block 7. Submit to the REC Supervisor for review and signature. In the remaining block, record pertinent information as applicable. If MRC A-2R has been performed, record reducer setting. For MRC A-3R, record demand valve actuation pressure. For 72M-1R or 72M-2R, record reducer setting and safety relief valve setting. 4-8 REVISION 1

87 PAGE NO. REENTRY CONTROL (REC) LOG MK 25 MOD 2 UBA ACTIVITY REC NO. RIG NO. JUSTIFICATION START DATE OF COMPLETION REMARKS Figure 4-3. Reentry Control Log, MK 25 Mod 2 UBA. (Locally reproduce as required) REVISION 1 4-9

88 4-10 REVISION 1 UBA Serial Number MK 25 MOD 2 UBA MAINTENANCE HISTORY FORM Action: MRC code, Corrective Maintenance Table number, or description of work performed. Comments section may be used to record data such as REC number, results of A-2R, A-3R, and/or 18M-1R, or other pertinent information. Action Date Name/Signature Comments Figure 4-4. Maintenance History Form (Sample). (Locally reproduce as required) SS600-A3-MMA-010/53833

89 4.4 MAINTENANCE REQUIREMENTS Repair Parts. Only those repair parts authorized for use with the MK 25 Mod 2 UBA shall be used Rubber Repair Parts. Rubber repair parts can deteriorate with age and adverse storage conditions. To ensure the integrity of any rubber repair part used, the following procedures shall apply: Protect rubber repair parts from direct light (natural and artificial) and extreme temperature and humidity changes. Store repair parts in their original or sealable plastic bags until ready for use. Prior to installing rubber repair part, carefully inspect for nicks, cuts, gumminess or any other signs of deterioration. Discard any part that appears damaged. After installation, leak test the affected component using either the dip test or soap solution technique. Prior to operational use of the MK 25 Mod 2 UBA, external O-rings shall be visually inspected for damage and proper lubrication. Ensure O-rings and O-ring grooves are clean and free of foreign particles. As applicable, lubricate O-rings sparingly, as excess lubrication can cause fouling. Never remove O-rings with screwdrivers or other metal picks. Do not over stretch O-rings during installation. After installation, ensure the O-ring is not twisted Overhaul Kits. Because of the number of replacement parts needed during performance of the overhaul MRCs, overhaul kits have been developed. These kits contain every replacement part necessary for a specific overhaul action and are ordered using one order number. Kits are available for overhaul of the demand valve assembly, cylinder valve, oxygen reducer, and flexible gauge line assembly, as well as the periodic replacement of all exposed O-rings and one-way valve discs. See Table Test Equipment and Tools. Only high quality tools should be used in performing maintenance actions. "High quality" is used to describe tools that do not chip, scratch, or lose their plating easily. Tools used for the MK 25 Mod 2 UBA must be cleaned (remove oil, grease, and dirt) and designated for O 2 use only. Table 4-1 lists all tools and test equipment required for maintenance on the MK 25 Mod 2 UBA Torque Specifications. Several components of the MK 25 Mod 2 UBA, when assembled, shall be tightened to measured values to ensure complete assembly of the component while avoiding damage. A table of these torque specifications can be found in Table Torque Adjustment When Using a Socket. When the torque wrench is used with a socket, no adjustment to the torque wrench setting is required Torque Adjustment When Using a Crowfoot. When the torque wrench is used with a crowfoot, the torque wrench setting must be adjusted to obtain the desired torque. Use the formula RS = (A/(A+B))*T, where RS will be the torque wrench setting to obtain the required torque, T. The lengths A and B are determined as shown in Figure 4-5. Ensure A and B measuring units are both the same, i.e., inches, centimeters, etc. Figure 4-5. Torque Adjustment. REVISION