Relief valve opens automatically, relieving system pressure to prevent over pressurization of a system. Process pressure acts against the bottom of the disc. As pressure exceeds the setpoint for the valve, established by a spring in most cases, the disk is pushed upward. When system pressure returns below the valve's setpoint, the spring push back the of the disc forcing it shut. By adjusting the tension on the spring, the setpoint can be adjusted. 
 

STANDARDS ASME, BS/DIN and IBR codes. 
DESIGN AND TESTED as per API-526/527.
WORKING PRESSURE AND TEMPERATURE Maximum pressure of 500 kg/cm2 and a Temperature of 4500C
MATERIAL such as C.I., C.S., SS-304/316, Hastelloy, B & C, Alloy-20,and to suit special corrosive applications valves are manufactured in PVC, Polypropylene etc..