HEAD PRESSURE CONTROL VALVES

Transcription

1 May / BULLTIN -- HAD PRSSUR CONTROL VALVS LAC-, LAC--DS, LAC- and LAC-

2 Page / BULLTIN -- HAD PRSSUR CONTROL VALVS The LAC valves are non-adjustable head pressure control valves. They are designed to maintain head pressure during low ambient conditions. The LAC valves limit the flow of liquid refrigerant from the condenser while at the same time regulating the flow of discharge gas around the condenser to the receiver. The valve designation LAC stands for Low Ambient Control. OPRATION LAC- The LAC- is a three way modulating valve. As shown in Figures and, the discharge pressure bleeds around the pushrod to the underside of the diaphragm. The discharge pressure opposes the dome pressure. When the outdoor ambient falls, the condensing pressure falls. This causes the discharge pressure to fall as well. When the discharge pressure falls below the dome pressure, the valve modulates open to the discharge port which allows discharge gas to bypass the condenser. Mixing of the discharge gas with the liquid creates a high pressure at the condenser outlet, reducing the flow and causing liquid to back up in the condenser. Flooding the condenser reduces the area available for condensing. This reduction in effective condenser surface area results in a rise in condensing pressure. During summer conditions, the discharge pressure is high thus closing off the discharge port. Hence, there is full liquid flow from the condenser to the receiver. LAC- and LAC- The LAC- and LAC- are also three way modulating valves. As shown in Figure, the receiver pressure acts under the diaphragm. As the receiver pressure drops below the valve setting, the seat moves away from the discharge port allowing discharge gas to bypass the condenser. This discharge gas warms the liquid in the receiver and raises the pressure to the valve setting. At the same time discharge gas is bypassing the condenser, liquid flow from the condenser is restricted which allows liquid to back up in the condenser. Flooding the condenser reduces the area available for condensing thus raising the condensing pressure. During summer conditions, the seat closes off the discharge port due to high pressure in the receiver. Therefore, there is full liquid flow from the condenser to the receiver. APPLICATION PRSSUR STTINGS These valves are available with three standard settings which should handle the majority of applications: psig for R-a; psig for R-, R-C and R-; and psig for R-A, R-A and R- The LAC valves can also be used with other commonly used refrigerants including A. Generally, standard settings may be used for these refrigerants but special settings may be preferred for some applications. LAC- and LAC--DS The standard element is a nonadjustable dome element as shown in Figure. The LAC--DS has a dual setting feature which allows a choice between two fixed settings, see Figure. The DS element has an internal spring which is set to maintain the lower setting. The element is then charged with air to obtain the higher setting and the capillary tube is pinched and fused. An example is an LAC--DS-/. If the capillary tube is left intact the valve will maintain a psig setting. If the capillary tube is clipped and fused again, the valve will maintain a psig setting. It is important to fuse the capillary tube tip after clipping to prevent moisture from entering the element. FIGUR FIGUR DISCHARG DISCHARG FOR US ON RFRIGRATION and/or AIR CONDITIONING SYSTMS ONLY Bulletin --, May, supersedes Bulletin --, dated August, and all prior publications COPYRIGHT BY SPORLAN VALV COMPANY, WASHINGTON, MISSOURI

3 BULLTIN -- / Page FIGUR returned to the receiver when high ambient conditions prevail. If the receiver is too small, liquid refrigerant will be held back in the condenser during high ambient conditions and excessively high discharge pressures will be experienced. If the manufacturer of your equipment provides charging information it should be used. However, if not provided, Sporlan Bulletin -- discusses two methods of calculating the correct amount of extra charge along with a method of charging a system with this type of head pressure control. DISCHARG LAC- and LAC- The standard element is a nonadjustable dome element as shown in Figure. However, there are many valves in the field with non-adjustable remote bulbs indicated by an ÒRÓ following the valve setting. s and elements with the remote bulb are available on special order. The valve designation and setting are stamped on the valve body. See the Designation section on Page for ordering information. Also, there are many valves in the field with special settings. These valves should be replaced with the same valve to ensure satisfactory system performance. RFRIGRANT MIGRATION During an off cycle there is a potential for refrigerant to migrate from the warm receiver to the cold condenser. An auxiliary check valve should be used in the liquid line between the LAC and the receiver to prevent this from occurring. See Figure SLCTION When selecting these valves it is necessary to consider the valveõs capacity when it is controlling at the minimum ambient design temperature. The minimum ambient design temperature is a factor because the bypassed discharge gas must heat up the subcooled liquid leaving the condenser to maintain the receiver pressure. This subcooled liquid will approach the ambient temperature. It is the flow of the discharge gas and liquid mixture flowing through the valve at the minimum design ambient conditions that will determine the valveõs capacity. Once the valveõs capacity and pressure drop have been determined at minimum design ambient conditions the capacity of the valve during high ambient conditions should be checked to determine the pressure drop of the valve with full liquid flow. XAMPL: Select a LAC valve for a R-, ton unit with a minimum design ambient temperature of - F. The LAC- has a capacity of. tons at a psi drop across the valve according to the Low Ambient Capacity Table on Page The LAC- also has a capacity of. tons at a psi drop across the valve according to the High Ambient Capacity Table on Page The LAC- is the correct selection. FIGUR RFRIGRANT CHARG When Òrefrigerant sideó head pressure control is utilized on a system, two additional considerations must be completely analyzed. First, there must be the correct amount of refrigerant to flood the condenser at the lowest expected ambient and still have sufficient charge in the system for satisfactory operation. A shortage of refrigerant will cause discharge gas to enter the liquid line and very little refrigerant will be able to pass through the expansion valve port, thus refrigeration will cease. Too much charge doesnõt cause any operating difficulties during low ambient conditions; however, this will cause high head pressures during high ambient conditions when head pressure control is not required. COMPRSSOR LAC CHCK VALV Secondly, a receiver is required of sufficient capacity to hold all of the liquid refrigerant in the system, since it will be

4 Page / BULLTIN -- INSTALLATION INSTRUCTIONS VALV LOCATION / PIPING SUGGSTIONS Figure is a piping schematic only to illustrate the general location of the LAC valve. In most cases the valve is located at the condensing unit. When the condenser is remote from the compressor, the usual location is near the compressor. Sporlan recommends that recognized piping references be consulted for assistance in piping procedures. Sporlan is not responsible for system design, any damage arising from faulty system design, or for misapplication of its products. If these valves are applied in any manner other than as described in this bulletin, the Sporlan warranty is void. BRAZING PROCDURS Any of the commonly used brazing alloys for high side usage are satisfactory. However, when soldering or brazing, it is very important that the internal parts be protected by wrapping the valve with a WT cloth to keep the body temperature below F. Also, when using high temperature solders, the torch tip should be large enough to avoid prolonged heating of the copper connections. Always direct the flame away from the valve body. TST AND OPRATING PRSSURS xcessive leak testing or operating pressures may damage these valves and reduce the life of the operating members. For leak detection an inert dry gas such as nitrogen or CO may be added to an idle system. CAUTION: Inert gases must be added to the system carefully through a pressure regulator. Unregulated gas pressure can seriously damage the system and endanger human life. Never use oxygen or explosive gases. WARNING: Serious injury could result from an explosion caused by the rapid expansion of trapped liquid refrigerant subjected to high temperature. ALWAYS OPN OR VNT TH SYSTM BFOR APPLYING HAT TO RMOV SYSTM COMPO- NNTS. Break the element charging cap tube on valve dome by hand or with a clean cut tool. DO NOT use side cutters which may seal the opening. The maximum pressure that these valves can withstand without internal damage is psig for the LAC- and LAC-, and psig for the LAC- Care must be taken to keep test or operating pressures below these values. UNDRWRITRS LABORATORIS The LAC valves are recognized components under UL Guide Number SFJQ, UL File Number SA The maximum rated pressure is psig ( kpa) for the LAC- and LAC-, and psig (kpa) for the LAC- Port Size Inches Sizes ODF - Inches Condenser SPCIFICATIONS / / / LAC- / / / / / / / / / / LAC- / / / / -/ -/ -/ / / LAC- / -/ -/ -/ Standard Settings psig,, or Replacement lements Not Available Non-adjustable Dome lement: DL-(specify setting) or Non-adjustable Remote Bulb lement: RL-(specify setting) VALV DSIGNATION LAC - - DS - / / x / x / ODF Low Ambient Control LAC - - R / x / x / ODF Low Ambient Control Size Size Dual Setting Delete for standard dome element Setting (psig) Setting(s) (psig) Specify one setting for standard dome element Indicates Remote Bulb Model - Delete for standard dome element Condenser Condenser Solder Solder

5 BULLTIN -- / Page DIMNSIONS LAC- LAC--DS LAC- Fitting Size A B C D /" or /" ODF.... Fitting Size A B C D /" or /" ODF.... Fitting Size A B C D D L R L /" ODF.... /" ODF.... /" ODF... -/" ODF... LAC- Fitting Size -/" ODF Condenser & Fitting Size A B C D D L R L /"... -/".. LAC-. LAC--DS. C D C D A B A B LAC- and LAC-.. (R L) (D L) C D. A B

6 Page / BULLTIN -- ( Setting - psig) () a () A () A () Minimum Pressure Drop Ambient Design Across Temperature - F psi HAD PRSSUR CONTROL VALV CAPACITIS Low Ambient (Winter) Capacities - Tons of Refrigeration LAC-, LAC- and LAC- Capacities are based on F vaporator Temperature and the valve setting as shown. ( Setting - psig) Minimum Pressure Drop Ambient Design Across Temperature - F psi LAC A. () C.. () () ()

7 HAD PRSSUR CONTROL VALV CAPACITIS High Ambient (Summer) Capacities - Tons of Refrigeration LAC-, LAC- and LAC- Capacities are based on F vaporator Temperature and F Condensing Temperature. BULLTIN -- / Page a A Pressure Drop Across psi Pressure Drop Across psi LAC A... &... A C & POSSIBL CAUS. Insufficient refrigerant charge to adequately flood the condenser Malfunction - LOW Head Pressure. LAC fails to close due to:. See below: RMDY. Charge system according to Manufacturers Specifications or if not available, use Bulletin -- a. Foreign material in the valve a. Cause the LAC to open by raising the condenser/ receiver pressure above the valve setting by cycling the condenser fan. If the foreign material is not dislodged, the valve may be disassembled and cleaned after properly isolating the valve. b. Loss of air charge in the element b. Replace the element (except LAC-, replace valve). Wrong setting on the LAC (e.g. psig on R- system). Replace element with the correct setting (except LAC-, replace valve) line to the LAC is restricted Remove restriction in fitting(s) or line POSSIBL CAUS Malfunction - HIGH Head Pressure. Dirty condenser coil. Clean coil. Air on condenser blocked off. Clean area around unit RMDY. Too much refrigerant charge. Remove charge until proper head pressure is maintained Undersized receiver Check the receiver capacity against refrigerant required to maintain desired head pressure Non-condensible (air) in the system Purge from system Liquid port or liquid line plugged Remove blockage in port or liquid line Wrong setting on the LAC (e.g. psig on R-a system). Spring overheated during installation, increasing the valve setting SRVIC INSTRUCTIONS Replace the element with the correct setting (except LAC-, replace valve). Replace the LAC. Condenser fans not running. Repair or replace fan motor