Safety & Relief Valves — API 526

What are Safety & Relief Valve?

A pressure relief valve holds a disc on its seat with a spring set to a chosen pressure. When system pressure reaches the set point, the valve lifts and discharges fluid until pressure falls, then recloses. Safety valves pop open fully for gas and steam; relief valves open in proportion for liquids; safety-relief valves serve both. Conventional valves are affected by back-pressure, while balanced bellows valves compensate for it. API 526 standardises orifice letters, sizes, ratings and dimensions for flanged steel valves.

Key features

• Conventional and balanced bellows spring-loaded designs
• API 526 orifice designations D to T, inlet NPS 1–8
• Open or closed bonnet; lifting lever and test gag options
• Set pressure tested and sealed at works
• Seat tightness tested to API 527

Specification

Applications

• Pressure vessel and heat exchanger protection
• Steam boiler and header overpressure protection
• Pump discharge and thermal relief
• Compressor and gas systems
• Storage tanks and process piping

Safety valve vs relief valve

A safety valve opens with a rapid full lift, called pop action, and is used for compressible fluids such as steam, air and gas. A relief valve opens gradually in proportion to overpressure and is used for liquids. A safety-relief valve is designed to work in either mode. Selection depends on the fluid, the required relieving capacity and the back-pressure at the outlet.