Safety Relief Valve - 3/8 MPT - 500 PSI A safety relief valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure exceeds preset limits. Excess pressure is vented out through discharge fitting, preventing damage to pump. Designed for self-cleaning of circular area chamber and piston head. Water continues to circulate, eliminating build up of mineral and waste products. Adjustable set screw allows setting relief valve for discharge at your specific pressure. Stainless steel spring. All safety relief valves are tested but are not preset.