Safety Valves

A safety valve (or safety relief valve) is a self-acting protective device that opens automatically when system pressure reaches a preset limit, discharging fluid to relieve the excess and prevent damage to vessels, boilers and pipework. It is a last line of defence against overpressure and its correct selection, setting and certification are usually a legal requirement on pressure equipment. The valve reseats once the pressure falls back to a safe level.

The behaviour on opening distinguishes the types. A safety valve for compressible fluids such as steam and gas pops fully open at the set pressure to relieve quickly, aided by a huddling chamber. A relief valve for liquids opens progressively in proportion to the overpressure. A safety relief valve is suitable for either service. Valves are supplied conventional (spring-loaded), balanced-bellows (to compensate for back-pressure) or pilot-operated for high capacity and tight sealing near the set point.

Applications cover steam boilers and steam systems, air and gas receivers, process vessels and reactors, pressurised storage and refrigeration. The set pressure, the relieving capacity and the discharge arrangement are determined by the protected equipment and by the applicable pressure-equipment rules.

Design, capacity certification and testing follow standards such as EN ISO 4126 and API 526, 520 and 527, with flanged connections to EN 1092 or ASME B16.5. Bodies and trim are made in cast and forged carbon steel, stainless steel and bronze, with seat materials selected for tight shut-off in the service. When specifying, provide the set pressure, the fluid and temperature, the required relieving capacity and the inlet and outlet connections, and we can propose a certified valve for the duty.