Under several possible conditions of malfunction, high pressures can occur in parts of the system and mechanical relief devices are advised or mandatory. The requirements which must be observed are detailed in European Safety Standard EN378 (2008) and the Institute of Refrigeration Safety Codes. The standard form of relief valve is a spring-loaded plunger valve. Plunger-type relief valves, if located outdoors, should be protected from the ingress of rain, which may corrode the seat. Steel valves, when installed, should have a little oil poured in to cover the seat as rust protection.

To prevent overpressure within a compressor, a relief valve or bursting disc is often fitted between the inlet and discharge connections.

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