Norgren General Purpose Pressure Relief Valves

Relief valves are used in compressed air systems to retard excessive air pressure buildup and thereby help prevent damage to system components. Relief pressure is controlled by the adjusting knob (1). Clockwise rotation increases and counterclockwise rotation decreases the relief pressure setting. 

Inlet pressure is applied to the bottom of the diaphragm (2) and tends to move the diaphragm upward and off the diaphragm seat (3). The relief spring (4) applies a downward force on the diaphragm and tends to hold the diaphragm down against the seat. If the air pressure force becomes greater than the relief spring force, the diaphragm will move upward away from the seat. This allows air to escape through the outlet port. When the inlet air pressure decreases to the relief pressure setting, the downward force of the relief spring becomes greater than the upward force of the inlet air pressure. The diaphragm then moves down against the seat, preventing further relief flow.