Diaphragm Accumulators

Transcription

1 Diaphragm Accumulators

2 HYDAC Diaphragm Accumulators Index Page 1. Description 3 Introduction 3 Construction 3 2. Applications 4 3. Technical Data 6 Operation 6 Technical Specifications 6 Temperature Effect 6 Formulas for Sizing Accumulators 7 Sizing Example 7 4. Installation Requirements 8 5. Model Code 9 6. Welded Type (non-repairable) Specifications Threaded Type (repairable) Specifications 11 2

3 1. DESCRIPTION INTRODUCTION HYDAC diaphragm accumulators utilize the compressibility of a gas (nitrogen) in storing hydraulic energy. The gas is required because fluids are practically incompressible and thus, can not store energy by themselves. The diaphragm is utilized to separate the gas and the fluid sides of the accumulator The diaphragm accumulator functions by drawing in fluid from the hydraulic circuit when the pressure increases and thus, compresses the gas. It returns this energy to the circuit as the pressure decreases by the expansion of the gas. A poppet is incorporated into the diaphragm to prevent its extrusion through the fluid port. HYDAC manufactures two types of diaphragm accumulators: welded (non-repairable) threaded (repairable) These have been successfully applied to both industrial and mobile applications in energy storage, maintaining pressure, leakage compensation, and vehicle hydraulic systems (e.g. brake and suspension). CONSTRUCTION Welded Type gas valve accumulator shell diaphragm poppet fluid port It consists of: an electronic beam welded shell with gas charging valve or alternately, completely sealed. Fluid ports are available in various thread configurations. a flexible diaphragm to separate the gas and fluid sides. a poppet. Threaded Type gas valve accumulator shell locking ring diaphragm poppet fluid port It consists of: a forged upper section with the gas valve. a forged lower section with the fluid port. a locking ring to fasten the upper and lower sections together. a replaceable, flexible diaphragm to separate the gas and fluid sides. a poppet Diaphragm Materials Not all fluids are compatible with every elastomer at all temperatures. Therefore, HYDAC offers the following choice of elastomers: NBR (Standard Nitrile) LT-NBR (Low Temperature Nitrile) ECO (Epichlorohydrin) IIR (Butyl) FPM (Fluorelastomer) others available upon request. Corrosion Protection HYDAC offers internal and/or external protective coatings. If this is insufficient, stainless steel is also available. Mounting Position Diaphragm accumulators by design may be mounted in any position. In systems where contamination is a problem, we recommend a vertical mount with fluid port oriented downward. System Mounting HYDAC diaphragm accumulators are designed to be screwed directly onto the system. We also recommend the use of our mounting components, refer to Mounting Components brochure # A 3.502, to minimize risk of failure due to system vibrations. 3

4 2. APPLICATIONS HYDAC diaphragm accumulators have been applied successfully in the following industries: Agriculture Forestry Machine Tools Mining Mobile Equipment Off Road Equipment Some examples are shown here and on the next page. HYDAC welcomes the opportunity to work with you on your application. A diaphragm accumulator is used to support peak demand and for emergency supply in the event of a pump failure With hydraulic suspensions, diaphragm accumulators are used to absorb shock. Diaphragm accumulators can enhance motion control and dampen vibration. 4

5 This picture shows two energy storage applications on fatigue testing equipment. These pictures show a heavy duty shock application. 5

6 3. TECHNICAL DATA OPERATION Describing the operation of diaphragm accumulators: 1 The diaphragm is precharged with nitrogen. This causes the poppet to close, preventing the diaphragm from extruding out of the fluid port. 2 Accumulator at maximum working pressure. The difference in volume ( V) between the maximum and the minimum working pressure corresponds to the effective fluid volume: 3 When the minimum working pressure is reached, a small amount of fluid should remain in the accumulator. This is to prevent the poppet from impacting the base on each cycle. Thus, p 0 should always be lower than p 1. V = V1 - V2 TECHNICAL SPECIFICATION Maximum Working Pressure Please refer to tables on pages 10 and 11. In other countries maximum working pressure may be different. Maximum Allowable Pressure Ratio Ratio of max. working pressure (p 2 ) to gas precharge pressure ( p 0 ). welded type: size to 2 8 : 1 size 2.8 and : 1 threaded type all sizes 10 : 1 Nominal Volume (size) Please refer to tables on pages 10 and 11. Effective Gas Volume (V 0 ) Corresponds to the gas volume. Recommended Gas Precharge Pressure for energy storage: p 0 = 0.9 x p 1 p 1 = minimum working pressure for shock absorption: p 0 = (0.6 to 0.9) x p m p m = median working pressure at free flow for pulsation dampening: p 0 = (0.6 to 0.8) x p m p m = median working pressure TEMPERATURE EFFECT To ensure that the recommended precharged pressure is maintained, even at relatively low or high operating temperatures, the gas precharge pressure should be adjusted for temperature. The formulas below relate the precharge temperature (T 0 ) to the operating temperature (T). Please refer to the sizing example on page 7. V0 P2 V2 P1 V1 V Effective Fluid Volume Volume of fluid available between the working pressure p 2 and p 1. Fahrenheit p 0,T0 = p 0,T2 x ( T ) T p 0 = gas precharge pressure p 1 = minimum working pressure p 2 = maximum working pressure V 0 = effective gas volume of the accumulator V 1 = gas volume at p 1 Fluids Mineral oil, hydraulic oil, water, water-glycol, and water emulsions. For other fluids, please consult HYDAC. Operating Temperature Selection of the shell material and elastomer depends on the operating temperature range of the unit. For selection, please refer to pages 8 and 9. T 0 = precharge temperature in F T 2 = maximum operating temperature in F p 0,T 0 = gas precharge pressure at precharge temperature p 0,T 2 = gas precharge pressure at maximum operating pressure Celsius p 0,T0 = p 0,T2 x ( T ) T V 2 = gas volume at p 2 T 0 = temperature at precharging T 1 = minimum operating temperature T 2 = maximum operating temperature Flow Rate The maximum allowable flow rate depends on the accumulator size. For selection, please refer to pages 10 and 11. T 0 = precharge temperature in C T 2 = maximum operating temperature in C p 0,T 0 = gas precharge pressure at precharge temperature 6 p 0,T 2 = gas precharge pressure at maximum operating temperature

7 FORMULAS FOR SIZING ACCUMULATORS The compression and expansion processes taking place in hydropneumatic accumulator are governed by the general gas laws. The following applies for ideal gases: p 0 x V n 0 = p 1 x V n 1 = p 2 x V n 2, where the time related change of state is represented by the polytropic exponent n. For slow expansion and compression processes which occur almost isothermically, the polytropic exponent can be set at n=1. For rapid processes, the diabetic change of state can be calculated using n = k = 1.4 (for nitrogen as a diatomic gas) (1. For pressures above 3000 psi the real gas behavior deviates considerably from the ideal one, which reduces the effective fluid volume V. In such cases a correction is made which takes into account a change in the adiabatic exponent (k). By using the following formulas, the required gas volume V 0 can be calculated for various calculations. Pressures of up to 150 psi must always be used as absolute pressures in the formulas. Calculation Formulas V V0 polytropic: = isothermal: (n=1) adiabatic: (n = k = 1.4) V0 = P1 V0 = ( ) ( ) P1 V ( ) ( ) 1/n 1/n P2 P2 V ( ) ( ) P P2 Correction factors to take into account the real gas behavior (2 V 0,real = C i x V 0,ideal or V real = V ideal C i for adiabatic change of condition: V 0,real = C a x V 0,ideal or V real = V ideal C a 1 An estimate of the accumulator size and a selection of precharge pressure can be calculated similar to the sample shown. For more accurate sizing and design assistance, please contact HYDAC. 2 The correction factors can be taken from the graphs in the next column, depending on the pressure ratio p 2 /p 1 and the maximum working pressure p 2, which is given as a parameter, for an isothermal or adiabatic change of condition. correction factor Ci correction factor Ca Correction factor for isothermal change of condition max working pressure p2 = 0bar (5800psi) 300 bar (4350 psi) 200 bar (2900 psi) max working pressure p2 = 0bar (5800 psi) 300 bar (4350 psi) 200 bar (2900 psi) SIZING EXAMPLE pressure ratio p 2 /p 1 Correction factor for adiabatic change of condition pressure ratio p 2 /p 1 A brake cylinder has to be rapidly operated by means of an accumulator. The system must operate between 3000 psi and 1500 psi. The required fluid volume to operate properly is 15 in 3. The maximum operating temperature is 1 F while the minimum is 50 F. Given: max. working pressure p 2 = 3000 psi min. working pressure p 1 = 1500 psi effective fluid volume V = 15 in 3 max. operating temperature T 2 = 1 F min. operating temperature T 1 = 50 F Required: 1 necessary accumulator size, taking into account the real gas behavior 2 gas precharge pressure p 0 at 68 F (T 0 ) Solution: Since it is a rapid process, the change of condition of the gas can be assumed to be adiabatic. 1 Determination of gas precharge pressure p 0,T2 = 0.9 x p 1 = 0.9 x 1500 = 1350 psi. In order to maintain the minimum working pressure (p 1 ), one must calculate the precharge pressure at T 1. T p 0,T 1 = p 0,T 2 x ( T ) = 1350 x = 1148 psi 1150 psi Determination of the required gas volume: V 0, ideal = 1150 = = 46.5 in 3 ( ), (T1) P1 V ( ) ( ) , (T1) P2 15 ( ) ( ) Taking into account the real gas p 0 = 2 - Ca 1.16 p 1 behavior: V 0,real = C a x V 0, ideal = 53.9 in 3 Selected: Diaphragm accumulator SBO (60 in 3 ) b) Determination of the gas precharge pressure p 0 at 68 F: T0 + p 0,T 0 = p 0,T2 x ( T ) = 1350 x 68 + ( ) = 1188 psi Selected: Gas precharge pressure p 0,T psi 7

8 4. INSTALLATION REQUIREMENTS General Suggestions WARNING! Hydraulic accumulators are pressurized vessels and only qualified technicians should perform recommended repairs. Always drain the fluid completely from the accumulator before performing any work, such as recommended repairs (see Maintenance Instructions) or connecting pressure gauges. Never weld, braze, or perform any type of mechanical work on the accumulator shell. Precharge new or repaired accumulators with dry nitrogen to the proper gas precharge pressure (P 0 ). For more complete details, please refer to HYDAC s Operating and Installation Instructions. Country of Installation Pressure vessel codes vary depending upon the country of installation. In the United States and Canada pressure vessels are governed by ASME pressure vessel code. HYDAC manufactures according to these standards. For installation in countries outside of the United States, please consult HYDAC for the appropriate certifications*. The country of installation codes shown below are required for ordering: please refer to page 9.! CAUTION Elastomer Compatibility Table In order to maximize system performance it is important to match your system fluid and its temperature range with the appropriate elastomer compound. The table below illustrates the most common ones. For special requirements, please consult HYDAC. Operating Some Compound Temperature Typical Range Fluids NBR (BUNA N) 5 F to 180 F mineral oils 32 F to 180 F water and water-glycols LT-NBR (low temp. NBR) - F to 180 F mineral oils ECO (HYDRIN) -20 F to 0 F mineral oils IIR (BUTYL) -20 F to 200 F FPM (VITON) 5 F to 300 F Gas Charging Pressurized Vessel Use Dry Nitrogen Gas Only! phosphate esters brake fluids chlorinated hydrocarbons Notes: 1 The operating temperature range does vary with fluid types, please consult HYDAC for more specific fluid data. 2 The above typical fluids are some examples of the most common fluids, please consult HYDAC for specific data. 3 For other applications not listed, please consult HYDAC. 8 Argentina Australia Austria Brazil Canada Chile China Finland France Germany Great Britain (UK) Italy Japan Mexico Russia Sweden USA S F D K S/S1 S A9 L B A K M P E A6 R S * The European Community (EC) has the Pressure Equipment Directive (PED) that is being phased in. Contact HYDAC for details.

9 5. Model Code: Diaphragm Accumulators SBO E 4 / 112 S 210 CK 010 Series (see table) Size (see table) Configuration/Gas Port E1 = welded construction, rechargeable, HYDAC gas valve version 1 (M28 x 1.5) E2 = welded construction, factory precharged and sealed, non rechargeable (1 E4 = welded construction, rechargeable, HYDAC gas valve version 4 (8VI-ISO 4570) A6 = threaded construction, rechargeable, HYDAC gas valve version 1 (M28 x 1.5) Material Code Depending on application 112 = standard for oil service (mineral oil) Fluid Port 1 = carbon steel 3 = stainless steel (316) 4 = chemically plated carbon steel (water service) (2 6 = low temperature carbon steel (< -20 F) Shell 0 = synthetic coated carbon steel (water service) 1 = carbon steel 2 = chemically plated carbon steel (water service) (2 4 = stainless steel (316) 6 = low temperature carbon steel (< -20 F) Diaphragm Compound 2 = NBR (Buna N) 3 = ECO (Hydrin) 4 = IIR (Butyl) 5 = LT-BNR (low temperature Buna) 6 = FPM (Viton) 7 = others Country of Installation S = USA Others on request (refer to page 8) Maximum Working Pressure in bar (see table, for E2 design this may vary depending upon the gas precharge pressure) Connection Thread A = BSP (ISO 228) B = Metric (DIN 13) C = SAE (ANSI B 1.1) D = NPT (ANSI B 1.2) K = Hexagonal (3 CK = Standard SAE connection Gas Precharge Pressure (p 0 ) in bar (4 Not All Combinations Available Notes: 1) Up to size 1 2) Only wetted surfaces 3) For units with internal threads only 4) Only required for E2-model 9

10 6. WELDED TYPE (non-repairable) Series Max. Size Effective MAWP Wt. A ød (2 Thread F K (hex) Q p 2 :p 0 (liters) Gas Vol in 3 psi/bar lbs/kg in/mm in/mm SAE NPTF (3 in/mm gpm SBO 0 8 : SBO : SBO : SBO : SBO : SBO : SBO : SBO : SBO 1 8 : SBO : SBO : SBO : SBO : SBO : SBO : SBO 0 4 : SBO : / UNF 3/ /180 ( / UNF 3/ / /160 ( / /1 ( / /100 ( /16-12 UNF 3/ / /16-12 UNF 3/ /16-12 UNF 3/ /16-12 UNF 3/ /16-12 UNF 3/ /16-12 UNF 3/ ) Stainless steel version for chemical, water, and oil service 2) Diameter at electron beam weld may be up to larger 3) May be supplied with adapter

11 7. THREADED TYPE (repairable) Series Max. Size Effective MAWP Wt. A B ød Thread F K (hex) øl M N Q p 2 :p 0 (liters) Gas Vol psi lbs in in in SAE in in in in gpm in 3 bar kg mm mm mm mm mm mm mm SBO : / SBO : /350 ( / / SBO : /600 ( / / SBO : /0 ( / / SBO : / SBO 0 10 : / SBO 0 10 : /180 ( / / ) Stainless steel version for chemical, water, and oil service 11

12 Other Products from HYDAC s Accumulator Line Bladder Accumulators The bladder style accumulator is a great general purpose accumulator. It has a wide range of sizes for energy storage requirements and is well suited for shock applications. Nominal volume 1 qt. to 15 gal. Max. working pressure 3000, 5000 and up to psi Flow rate up to 480 gpm Piston Accumulators A wide range of piston accumulators is available. Piston position monitoring is available using proximity switches, extending piston rod or ultrasonic techniques. Auxiliary gas bottles are frequently used with piston accumulators to provide the required gas volume. Nominal volume 1 qt. to 100 gal. Max. working pressure 3000, 5000, and up to psi Flow Rate up to 2000 gpm Request catalog # Request catalog # Mounting Components HYDAC mounting components are used to mount all types of hydropneumatic accumulators safely and simply, regardless of the mounting position. Our wide range includes suitable mounting components for every type of hydro pneumatic accumulator. Mounting components are used primarily for the following: to fix the accumulator into position, to carry the weight of the accumulator, and to counteract the forces exerted by the hydraulic lines. HYDAC also offers base brackets for larger accumulators for proper support and isolation from system vibrations. The brackets incorporate a rubber support ring for this reason. All mounting components can be easily bolted to your system. Request catalog # Charging & Gauging To maintain system performance, HYDAC recommends a regular check of the gas precharge pressure. A loss in the gas precharge pressure will cause a drop in the system efficiency and could cause damage to the bladder, diaphragm or piston accumulator. By means of a charging and gauging unit, hydro-pneumatics accumulators are precharged with dry nitrogen or their existing gas precharge pressure is checked. For these purposes, a charging and gauging unit is connected to a commercially available nitrogen bottle via a flexible hose. The charging and gauging units incorporate a gauge, check valve in the charging connection, manual bleed valve and T-handle. Request catalog # Copyright 2000 HYDAC TECHNOLOGY CORPORATION - Brochure - Diaphragm Accumulators # / HYDAC CORPORATION 2280 City Line Road Bethlehem, PA Phone (610) Fax (610) powerup@hydacusa.com