We offer two standard types of pressure relief devices for air: A safety relief valve, or pop-off valve, is set to pre-determined pressure using a spring force to counteract the air pressure force.  When the force created from the air pressure becomes greater than the spring force, the valve ‘pops’ fully open and vents air to the atmosphere.  Safety relief valves are sized in such a manner that the valve will always have a greater flow capacity than the source creating the air pressure (i.e. an air compressor).  The valve will remain open until a reseat pressure is reached.  This reseat pressure varies with valve type and is usually between 35% to 75% of the set pressure.  Control Devices have eight series of valves that are manufactured in accordance with Section VIII of the ASME Boiler and Pressure Vessel Code.  Control Devices also manufacture a wide range of non-code valves.  See our Products section for information on the valve types. A relief valve is set to a pre-determined pressure with a spring force counteracting the force created by the pressure from the air.  When the force created from the pressure of the air becomes greater than the force of the spring, the valve will start to open and flow to atmosphere.  As the pressure continues to increase, the valve will open further, allowing more flow.  As the pressure decreases, the valve will close near the pressure at which it opened.