What Is a Check Valve?
A check valve allows fluid to flow in one direction only. It opens automatically when forward flow creates sufficient pressure and closes when flow reverses or stops. Check valves have no handwheel, actuator, or external operator; they are entirely self-actuating.
When to Use a Check Valve
Check valves are required downstream of pumps and compressors to prevent reverse flow when the equipment shuts down. They also protect equipment from backflow in gravity-fed systems, prevent contamination in chemical injection lines, and maintain system pressure in multi-source piping networks. Every piping system with a pump discharge line includes at least one check valve.
Specifications
| Feature | Details |
|---|---|
| Function | Prevent backflow (unidirectional flow) |
| Actuation | Self-actuating (no external operator) |
| Flow direction | One direction only (arrow on body) |
| Main types | Swing, lift (piston), dual plate (wafer), tilting disc, ball |
| Cast body standard | BS 1868, API 594 |
| Forged body standard | API 602, BS 5352 |
| Pressure classes | 150 to 2500 per ASME B16.34 |
| Body materials | ASTM A216 WCB, A352 LCB (low temp), A351 CF8M (SS) |
| Sizes | 1/2” to 60”+ |
Check Valve Types
Swing check: a hinged disc swings open with forward flow and swings shut under gravity and reverse flow pressure. Full bore design with low pressure drop. Standard for horizontal lines and large sizes. Governed by BS 1868.
Lift check (piston check): a piston or disc lifts off the seat when forward flow pushes it up. Higher pressure drop than swing check but better suited for pulsating flow (e.g., downstream of reciprocating compressors). Must be installed in horizontal lines with the disc moving vertically.
Dual plate (wafer check): two semicircular plates pivot on a central hinge pin. Compact, lightweight, and fits between flanges like a wafer. Faster closure than swing check, reducing water hammer. Covered by API 594.
Tilting disc: the disc tilts on an offset pivot rather than swinging through a full arc. Combines low pressure drop with fast closure. Used in large-diameter pipeline applications.
Ball check: a ball sits on a conical seat. Simple and effective for small-bore, low-pressure, or viscous fluid services.
Selection Criteria
| Check Valve Type | Best For | Pressure Drop | Closure Speed | Installation |
|---|---|---|---|---|
| Swing check | General service, large sizes | Low | Slow | Horizontal only |
| Lift/piston check | Pulsating flow, compressor discharge | Medium-high | Fast | Horizontal (disc vertical) |
| Dual plate (wafer) | Space-constrained, water hammer risk | Medium | Very fast | Horizontal or vertical |
| Tilting disc | Large pipelines, pump discharge | Low | Fast | Horizontal only |
| Ball check | Small bore, viscous fluids | Medium | Moderate | Any orientation |
Water Hammer Prevention
When a check valve closes too slowly, the reverse flow accelerates before the disc reaches the seat. The sudden stop creates a pressure surge (water hammer) that can damage piping, supports, and equipment. Dual plate and tilting disc check valves close faster and generate less water hammer than swing checks.
For critical pump discharge lines, spring-assisted or damped check valves provide controlled closure and minimize surge.
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