Pressure relief valves, or safety valves, are a simple but critical part in any air compressor system. Pressure relief valves are used to control and limit the pressure build-up in a system. If pressure exceeds the amount allowed by the pressure relief valve, the pressure relief valve will automatically open and release air until the pressure is reduced.
Why Do Pressure Relief Valves Matter?
Pressure relief valves keep everyone safe. If pressure within an air compressor system or air receiver tank gets too high, one or more components could explode. Pressure relief valves are used to prevent this from occurring.
The rated pressure of the pressure relief valve must not exceed the maximum allowable working pressure (MAWP) marked on the air pressure vessel. This requirement ensures the pressure relief valve will always open before the vessel reaches its maximum pressure tolerance.
In addition, the minimum relieving capacity of the pressure relief device must meet the requirements of the American Society of Mechanical Engineers (ASME) Code. ASME is the international leader in developing and revising codes associated with mechanical engineering.
How Do Pressure Relief Valves Work?
Pressure relief valves for air compressor systems are simple, spring-loaded mechanisms. When the inlet pressure force is greater than the spring load, the safety valve opens in proportion to the increase in pressure and allows air to “leak out” as needed.
Pressure relief valves for compressed air applications are direct-acting, which means they automatically react if the pressure gets too high. If excessive pressurization occurs, a disc seal is moved up by system pressure against a spring, which is holding the valve closed. If the compressed air force exceeds the force exerted by the spring, the valve disc is lifted off the valve seat and the valve discharges the compressed air to the atmosphere.
In accordance with the requirements of the ASME relief valve standard, the full discharge capacity of the valve typically will be achieved when the system pressure climbs to no more than 10% above the set pressure of the valve. Full shutoff must be achieved if the system pressure falls to below the set pressure value, usually set at 90%.
How To Test Pressure Relief Valves
To ensure pressure relief valves maintain their effectiveness over time, a set pressure function test should be carried out at least once per year. At VMAC, we recommend inspecting pressure relieve valves annually for signs of corrosion or loss of functionality.
The pressure relief valve tests are the responsibility of the user or operator, while test instructions should be supplied by the air compressor manufacturer. For example, VMAC’s manuals include test instructions to perform a pressure relieve valve inspection:
“To test the pressure relief valve functionality, turn the system on and bring it up to operating pressure. Pull the ring on the pressure relief valve to depressurize the system. Turn the system off, and ensure the system comes back to operating pressure when the system is restarted. If the pressure relief valve is showing loss of functionality, contact your local, authorized VMAC dealer for a replacement part. Relief valve failure can result in air/oil tank over-pressurization leading to system failure or rupture.”
If you are operating a system that is not a VMAC air compressor, check your manual or contact the manufacturer for detailed instructions on how to test your pressure relief valve.
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