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How Do You Test Pressure Relief Valves?


Volatile chemicals and gases require as a matter of law as well as a matter of safety a range of features and fail-safes that ensure that if pressure builds up in a tank that it will not cause major damage.

It is a legal requirement under the Dangerous Substances and Explosive Atmospheres Regulations 2002 that employers have mitigated the risk of substances that are flammable or explosive, and vacuum relief valves and other safety features help with this.

Testing that these features are working and suitable for the substances the tank is carrying is also of critical importance.


How Relief Valves Work

Relief valves are used on tanks that contain substances that become volatile under pressure and rely on particular atmospheric conditions. This can include liquid gasses such as liquid nitrogen, liquid oxygen and liquid petroleum gas, as well as oil and other flammable liquids.

If there are changes to the conditions in or around the take, such as a fire outside the tank, this can cause the substance to change and since gas takes up more space than liquid, this can compromise the tank, causing leaks, punctures and other collapses to its integrity.

A relief valve detects when the tank reaches a certain pressure and automatically channels excess gases away from the tank, typically to a burner or another excess tank where it can be stored safely.


How To Test

The simple way to test a valve is to calibrate the valve, by emulating the pressures it is likely to take. This can be done with a pneumatic pump or by using compressed air or nitrogen gas and a pressure gauge.

The three readings you will want to look into are:


·      Set Pressure: This is the pressure engraved on the valve itself when it will pop and release pressure rapidly, typically with a 3 per cent tolerance. It should not open all the way but rapidly open and close to filter out a small amount of excess.

·      Overpressure: This is the pressure where the valve will open fully and channel out excess gasses, with a tolerance of up to 10 per cent above the set pressure.

·      Blowdown Pressure: This is the pressure reading when the valve finally closes again and stops releasing gas.