Check Valve

A check valve, also called a non-return valve, allows flow in one direction only and closes automatically to prevent reverse flow. It is operated by the process fluid itself, without external actuation: forward flow opens the closure element, and flow reversal or loss of flow allows it to reseat by gravity, spring force or back pressure. Common types include swing, lift (piston), ball, dual-plate (wafer) and axial-flow (nozzle) check valves. They protect pumps and compressors from reverse rotation, prevent backflow and siphoning, and maintain prime in discharge lines. Selection considers cracking pressure, pressure drop, closing speed, installation orientation and the risk of water hammer and valve slam, which fast-closing spring-assisted or nozzle designs help reduce. Relevant standards include API 594 (wafer and dual-plate), API 6D, API 602 and ASME B16.34.

Examples

• Dual-plate check valve on a pump discharge
• Nozzle check valve on a compressor outlet
• Swing check valve in a water distribution main

Related terms

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