How to Order Check Valves
Check valves prevent reverse flow, and their correct specification depends on the valve type, the flow characteristics of the system, and the consequences of valve slam. Ordering a check valve without specifying the type, internal materials, or whether spring loading is required risks receiving a valve that slams on closure, causes water hammer, or does not seat properly at the available differential pressure.
This checklist covers the parameters required for ordering swing checks (BS 1868), piston/lift checks (API 602), dual-plate checks (API 594), and tilting disc checks for RFQs and purchase orders.
Core Attributes
These parameters must appear in every check valve line item on your RFQ or purchase order.
| Parameter | What to Specify | Example |
|---|---|---|
| Design standard | BS 1868 (cast flanged swing check), API 594 (wafer/lug dual-plate check), API 602 (forged piston/lift check). Also: API 6D (pipeline check valves). | BS 1868 |
| Check valve type | Swing check, piston (lift) check, dual-plate (wafer or lug), tilting disc | Swing check |
| Nominal size | NPS or DN | NPS 8 |
| Pressure class | Class 150, 300, 600, 900, 1500, or 2500 per ASME B16.34 | Class 150 |
| End connection | Flanged (FL) with face type: RF or RTJ. Butt-weld (BW). Wafer (W) or lug (L) for dual-plate. Threaded (NPT) or socket weld (SW) for forged piston checks. | FL-RF |
| Body-bonnet connection | Bolted bonnet (BB) or bolted cover. Pressure seal (PS) for high-class swing checks. | BB |
| Body material | Cast CS: ASTM A216 WCB/WCC. Low-temp: ASTM A352 LCB/LCC. Cast SS: ASTM A351 CF8/CF8M. Forged CS: ASTM A105. Forged SS: ASTM A182 F316. | ASTM A216 WCB |
| Internal components | Disc/clapper material, seat ring material, and hinge pin material. Specify by name: 13Cr, Stellite 6, Monel, Inconel 625. | 13Cr disc & seat |
| Body pattern | Straight pattern (standard) or Y-pattern (for piston/lift checks; lower pressure drop) | Straight pattern |
Optional / Special Attributes
Include these when the service, project specification, or client requirements demand it.
| Parameter | What to Specify | When Required |
|---|---|---|
| Spring loading | Spring-assisted closure. Specify closing pressure (cracking pressure) in bar/psi if critical. | Vertical upward flow, compressor discharge, systems prone to reverse flow surges |
| Non-slam / silent closing | Non-slam design with spring or dashpot mechanism. Specify maximum closing time if required. | Pump discharge, parallel pump systems, water hammer-sensitive systems |
| Dashpot | External or internal hydraulic dashpot for controlled closure speed | Large swing check valves (NPS 16+) on liquid service where slam damage is a concern |
| External lever & weight | Lever arm with adjustable counterweight for assisted closure | Large swing checks (NPS 8+) in horizontal pipe runs where gravity-assisted closure is needed |
| Cracking pressure | Minimum upstream pressure at which the disc lifts off the seat, in bar or psi | Low-pressure or gravity-flow systems, compressed gas service |
| Flow direction verification | Confirm arrow direction and installed orientation (horizontal, vertical up, or vertical down) | All check valve orders; ensures the valve type suits the installation orientation |
| NACE MR0175 / ISO 15156 | Sour service compliance with hardness and chemistry restrictions | H2S-containing environments |
| Fire-safe certification | API 607 fire-test certification | Hydrocarbon service, offshore |
| Certificates | EN 10204 Type 3.1 (MTR) or Type 3.2. Pressure test certificate per API 598. | Always specify; 3.2 for critical service |
Example Line Item
Correct:
8 pcs - Swing check valve, BS 1868, NPS 8, Class 150, FL-RF, BB, ASTM A216 WCB body, 13Cr disc & seat, external lever & weight
This line item defines: quantity and UOM, valve type, design standard, size, pressure class, end connection and face type, bonnet type, body material, internal component materials, and the closure assist mechanism.
Incorrect:
8 - Check valve 8 inch
This is missing the check valve type (swing, piston, dual-plate, or tilting disc), design standard, pressure class, end connection, body material, internal component materials, and whether any closure assist device is required. The supplier cannot determine what type of check valve to supply or what materials are needed.
Common Pitfalls
- Not specifying the check valve type. Swing check, piston check, dual-plate, and tilting disc valves have fundamentally different performance characteristics. Swing checks have the lowest pressure drop but the slowest closure; piston checks are best for pulsating flow (compressor discharge); dual-plate (wafer) checks are compact and lightweight for space-constrained installations; tilting disc checks offer fast closure with low pressure drop. The piping engineer must select the type; leaving it to the supplier results in the cheapest option, not the best one.
- Forgetting spring loading for vertical installations. A standard swing check valve relies on gravity to close the disc. In vertical-upward flow, gravity alone cannot close the valve, and the disc hangs open. Spring-loaded checks are mandatory for vertical installations and highly recommended for any application where flow reversal must be stopped quickly.
- Omitting lever and weight for large swing checks. Swing checks NPS 10 and above in horizontal runs benefit from an external lever and counterweight that accelerates disc closure. Without this mechanism, the large, heavy disc closes slowly and slams, causing water hammer, pipe vibration, and premature seat wear.
- Using wafer-type check valves where line maintenance requires removal. Wafer check valves are sandwiched between flanges and cannot be removed without separating the flanged joint and spreading the pipe. If the valve must be maintained in place, specify a flanged-end swing or tilting disc check instead. Alternatively, specify lug-type dual-plate checks, which can be unbolted from one side while the other flange remains supported.
Leave a Comment
Have a question or feedback? Send us a message.