Refrigeration Manual - HVAC and Refrigeration Information Links

This type of valve enables checking of the systempressure, or charging refrigerant without disturbingthe unit operation. An adaptor is necessary for thestandard serviceman’s gauge or hose connection to fitthe Schrader type valve.PRESSURE RELIEF VALVESSafety relief valves are required by many localconstruction codes. Various types of relief valves areavailable, and the system requirement may be dictated bythe local code requirement. Normally code requirementsspecify that the ultimate strength of the high side partsshall be a minimum of 5 times the discharge or rupturepressure of the relief valve, and that all condensing unitswith pressure vessels exceeding 3 cubic feet intervalvolume shall be protected by a pressure relief device.Discharge may be to the atmosphere, or it may be adischarge from the high pressure side of the system tothe low pressure side.A typical reseating type valve is shown in Figure 38.The valve opens at a preset pressure, and refrigerantis discharged until the pressure falls to the reseatingpoint.Some Copeland® brand compressors have reseatingtype pressure relief valves installed internally in thedischarge chamber which allow excessive pressuresto discharge to the suction chamber. A typical internaltype valve is shown in Figure 39.Rupture disc type relief devices have a thin disc which isdesigned to rupture at a given relief pressure, dischargingthe refrigerant to the atmosphere.FUSIBLE PLUGSA fusible plug is a safety device with a metal inserthaving a specified melting point. The allowable meltingpoint is defined by code, but normally it is the saturationtemperature of the refrigerant at a pressure no greaterthan 40% of the ultimate bursting pressure of therefrigerant containing vessel, or the critical temperatureof the refrigerant, whichever is lower .Fusible plugs are limited to units with pressure vesselsnot exceeding 3 cubic feet internal gross volume. Theyare used as a safety device in the event of fire, areresponsive to temperature only and will not protectagainst excessively high pressures.© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-12