Swing Check Valve
General / GeneralDefinition
A swing check valve allows flow in one direction and blocks reverse flow using a hinged disc that swings open on forward flow and closes under gravity and backpressure. The disc pivots on a hinge pin mounted inside the valve body, and its arc of travel resembles a door swinging open and shut. This is the most common and oldest check valve design, valued for its simplicity, low cost, and low pressure drop in the full-open position.
Working Principle
Forward flow creates a differential pressure across the disc, pushing it open against its own weight (and any spring or counterweight if fitted). The disc swings to a near-vertical position, creating a flow area nearly equal to the full pipe bore. When flow stops or reverses, backpressure and gravity push the disc back against the seat. The closing speed depends on the rate of flow reversal — rapid flow reversal causes the disc to slam against the seat, producing water hammer and potential seat damage. Some designs add a dashpot or external counterweight to moderate closing speed.
Key Components
| Disc (clapper) | Flat or slightly convex plate that swings on the hinge pin |
| Hinge pin | Pivot shaft supporting the disc; may be external or internal |
| Seat | Machined face in the body where the disc contacts for shutoff |
| Body | Houses the disc, hinge, and flow passage; globe or tilting-disc pattern |
| Cover / Bonnet | Provides access for maintenance; may house the hinge pin |
| Counterweight (optional) | External weight to assist closing or adjust slam speed |
| Dashpot (optional) | Hydraulic cushion to slow disc closure on rapid reversal |
Types & Variants
| Variant | Disc Design | Closing Speed | Typical Use |
|---|---|---|---|
| Plain swing check | Simple hinged disc | Uncontrolled — may slam | Low-velocity water, general service |
| Counterweighted swing | External weight on hinge arm | Faster or slower (adjustable) | Pump discharge, variable flow |
| Dashpot-damped swing | Hydraulic cylinder on hinge | Controlled, cushioned closure | Pump protection, water hammer prone systems |
| Tilting-disc check | Disc tilts at 15–30° off seat | Shorter stroke, less slam | High-velocity pump discharge |
Materials
Carbon steel (A216 WCB) for general oil, gas, and water service. Stainless steel (CF8M) for corrosive chemicals, seawater, and food-grade applications. Cast iron (A126) for low-pressure water and HVAC at the economy end. Bronze (B61/B62) for marine and small-diameter water. Seat facings: integral body seat for low-cost, Stellite overlay for erosive service, or elastomer-inserted seats for zero leakage on low-pressure applications.
Applicable Standards
API 594 (check valves — swing and tilting disc), API 600 (steel gate/globe/check), MSS SP-71 (gray iron swing check valves), MSS SP-80 (bronze check valves), BS 1868 (steel check valves). API 594 defines face-to-face dimensions and minimum flow areas for various patterns.
Applications
Pump discharge lines are the primary application — swing check valves prevent reverse flow and protect pumps from backspin when a pump trips offline. Cooling water systems use them on supply and return headers. In steam condensate return lines, swing check valves stop condensate from flowing backward into idle equipment. Process plant headers install swing check valves where multiple sources feed a common manifold, preventing cross-flow between sources. In low-velocity applications, a counterweighted or spring-assisted version ensures the disc does not flutter in partially-open positions.
Advantages
- Simple, reliable design with a long service history
- Low pressure drop when fully open — near full-bore flow
- Low cost compared to nozzle check or dual-plate designs
- Available in all common materials and pressure c