As the name implies, a pressure relief valve is a device designed to relieve the pressure on a system when it reaches a prescribed level.
An example of the use of a pressure relief valve is provided by procedures recommended for pressure testing of tanks at the installation site, prior to their introduction into the excavation. For a steel tank, the recommended air test pressure is 5 psig. A tank can tolerate pressure of this magnitude. However, if a greater amount of pressure were introduced into the tank, say, 15 or 20 pounds, the effect could be disastrous. The tank ends could be blown off.
To guard against this possibility when conducting such tests, installation contractors include a pressure relief valve in the test apparatus. The valve can be set to release when the pressure reaches a predetermined level. If pressure should reach that level, the valve will open, relieving the pressure.