Two closure mechanisms
A piston-lift check uses a guided piston or disc that lifts from the seat as inlet pressure overcomes its weight, friction and any spring force. The flow path passes through the seat region and changes direction inside the body.
A swing check uses a hinged disc that rotates away from the seat. In a suitable open position, the disc leaves a comparatively open passage. Hinge geometry, disc mass and travel govern the closing motion.
| Point | Piston-lift check | Swing check |
|---|---|---|
| Moving element | Guided lifting piston or disc | Disc rotating on hinge or pin |
| Flow route | Turns through lift-seat geometry | Passes around an open swinging disc |
| Pressure-loss tendency | Higher for comparable nominal size and bore | Lower for comparable nominal size and bore |
| Closure travel | Axial guided travel | Angular swing travel |
| Orientation sensitivity | Design-specific; gravity and guidance matter | Design-specific; hinge axis and gravity matter |
Cracking pressure belongs on the data sheet
The opening differential is set by moving-part weight, orientation, seat area, friction and spring force where a spring is fitted. It is not fixed by NPS or pressure Class. A low available differential can leave either design partly open and unstable.
State the maximum acceptable cracking pressure where the system is sensitive. If a spring-loaded check is required, give spring material, set range and orientation. Do not assume every piston check includes a spring or that every swing check is free swinging.
Check-valve slam is a system event
Reverse velocity can build while the closure member travels toward the seat. A late or rapid closure can create pressure transients, noise and mechanical load. Pump trip behaviour, line deceleration, compressibility, elevation and downstream equipment all influence the event.
A smaller travel or spring-assisted design may close earlier in some systems, but no pattern name guarantees non-slam performance. Where transients matter, provide the system deceleration or surge study and request closure-dynamic data for the proposed valve.
Confirm every installed orientation
Horizontal line, vertical upward flow and vertical downward flow impose different gravity forces. A construction suitable in one orientation may not close correctly in another. The approved drawing and installation instructions control the permitted position.
Give the pipe direction and flow arrow in the RFQ. For existing pipework, include nearby elbows, reducers and pump discharge geometry because disturbed velocity profiles can affect disc stability.
Selection data that separates the designs
Piston-lift construction can suit compact, guided closure where its pressure loss and orientation limits are acceptable. Swing construction can suit duties that benefit from a more open flow route, provided closure dynamics and installation are satisfactory.
FerraForge retains piston-check and swing-check as separate catalogue profiles. The RFQ should preserve that choice and include fluid density, viscosity and phase; minimum, normal and maximum flow; pressure and temperature; orientation; available differential; and transient conditions.
Specification checks
- Name piston-lift or swing construction.
- State horizontal or vertical orientation and flow direction.
- Provide minimum, normal and maximum flow plus fluid properties.
- State acceptable cracking pressure and whether spring assistance is required.
- Provide pump-trip or surge data where rapid flow reversal can occur.
Catalogue and RFQ
Standards publisher references
Published by Nordic Valves Ab Oy, the operator of FerraForge. These links describe the publishers’ official scope. Purchase documents must state the edition required by the project and include any amendments or owner specifications.
- API Monogram and APIQR programme documentsAmerican Petroleum Institute · Official standard titles and the API Monogram programme document register.
- ASME B16.34 - Valves - Flanged, Threaded, and Welding EndASME · Official scope covering valve pressure-temperature ratings, materials, dimensions, testing and marking.