For most pump discharge lines from NPS 2 to NPS 24, the default is a wafer check valve of the spring-assisted dual-plate type: short, light, and closed before much reverse flow builds up. Choose a tilting disc check valve where low head loss on a large line matters more than compactness, and a nozzle or center-guided silent check when several pumps share a header.
This guide goes deeper than our overview of check valve types.
Wafer Check Valve and Tilting Disc Designs
Wafer dual-plate: retained or retainerless
Two D-shaped plates hinge on a central pin, and a torsion spring closes them as flow slows. In the retained design, the pins pass through holes in the body wall sealed with threaded plugs, which can loosen and leak under thermal cycling and vibration; a retainerless body has no penetrations. Retained valves are common on chilled, condenser and general water. For hydrocarbon, steam, thermal oil or toxic service, or insulated lines where a weeping plug would go unnoticed, specify retainerless.
Heavy-duty dual-plate variants
For high-cycle or high-velocity duty, look for an independent spring on each plate, a lift-off geometry that raises the plate heel before it rotates so the seat is not scuffed every cycle, hardfaced seats and a lug or double-flanged body. A heavier spring is the simplest anti-slam upgrade but raises the velocity needed to hold the plates open, so recheck sizing.
Wafer single-plate and wafer tilting disc
A single disc sits in a short wafer body, hinged at the top or pivoted slightly off center so flow forces partly balance and the stroke stays short. Closure relies partly on gravity, making these less forgiving in vertical pipe, and the open disc projects past the body face, so check clearance.
Flanged tilting disc
A long flanged body carries a disc that pivots just off its center line onto an angled seat. The large flow area gives low head loss, and the short stroke closes much faster than a swing check; these serve mainly larger pump stations and mains. An optional oil dashpot slows final closure, but the pump must then tolerate brief reverse flow and backspin.
Comparison: Wafer, Tilting Disc, Swing and Silent Checks
| Design | Closure and slam resistance | Head loss, fully open | Length | Orientation | Typical fit |
|---|---|---|---|---|---|
| Wafer dual-plate, retained | Fast, spring-assisted | Moderate | Very short | Horizontal with pin vertical, or vertical up | HVAC and water service |
| Dual-plate, retainerless | Fast, no body penetrations | Moderate | Very short | As above | Hydrocarbon, steam, toxic service |
| Heavy-duty dual-plate | Fast; independent springs | Moderate | Short | As above | High-cycle pump discharge |
| Wafer single-plate or tilting disc | Medium; partly gravity-closed | Low to moderate | Short | Horizontal preferred | Compact discharges |
| Flanged tilting disc | Good; dashpot optional | Low | Long | Horizontal preferred | Large pump stations, mains |
| Swing (reference) | Slow; slams at high deceleration | Low to moderate | Long | Horizontal or vertical up | Gravity, low-deceleration lines |
| Silent, center-guided or nozzle (reference) | Fastest | Higher (globe), low (nozzle) | Short to medium | Most; confirm down-flow | Multi-pump headers, boosters |
Slam: Match the Valve to the System’s Deceleration
The bang is not the disc hitting the seat but the pipe stretching as reverse flow, built up while the disc was still moving, stops almost instantly. A peer-reviewed method in Journal AWWA (Ballun, 2007), based on Utah Water Research Laboratory tests, has two steps:
- Estimate how fast the water column decelerates after the pump stops, in m/s2.
- Read each candidate’s maximum reverse velocity Vr from its dynamic characteristic curve at that deceleration, and convert it to surge with the Joukowsky equation, ΔP = ρ × a × Vr.
The paper puts single-pump, low-head systems below about 6 m/s2 and high-head or multi-pump systems at up to about 12 m/s2. Overall, spring-assisted silent and dual-disc valves performed best and tilted disc next, though at moderate deceleration it was close to the dual-disc; swing and ball checks slammed hardest. Gravity-closed types tend to slam more in vertical pipe, and valves larger than the 8-inch test size will likely do worse.
For water in NPS 8 Schedule 40 steel, a = √(K/ρ) ÷ √(1 + K·D/(E·e)) gives roughly 1,300 m/s (K = 2.2 GPa, E ≈ 200 GPa, D/e ≈ 25), so each 0.1 m/s of reverse velocity adds about 1.3 bar (19 psi). For surge control beyond the check valve, see our water hammer prevention guide.
Worked Example: A Pump Lifting 45 m Through an NPS 8 Line
A single plant-water pump lifts 60 L/s into a tank 45 m above it through 75 m of NPS 8 Schedule 40 steel (ID 202.7 mm), with the check valve in a horizontal discharge run. A variable frequency drive turns the flow down to 30 L/s.
- Velocity. 0.060 m3/s ÷ 0.0323 m2 = 1.86 m/s at design and 0.93 m/s at turndown.
- Deceleration on power failure. A rigid-column estimate ignoring pump inertia, and so erring on the safe side, gives dV/dt ≈ g × (static head + friction) ÷ L = 9.81 × (45 + 2) ÷ 75 ≈ 6.1 m/s2, stopping forward flow in about 0.3 s. The drive’s ramp-down cannot help once power is lost.
- Surge. The paper’s 8-inch data at about 6.1 m/s2 gives reverse velocities of roughly 0.06 m/s (silent), 0.09 m/s (tilted disc), 0.11 m/s (dual-disc) and over 0.61 m/s (swing): about 0.8, 1.2 and 1.4 bar of surge for the first three, and 8 bar (115 psi) or more for the swing, on top of 4.4 bar of static head.
- Verdict. Dual-plate, tilting disc and silent valves all avoid slam; the swing check does not. On a three-pump header, a tripped pump’s branch sees the running pumps’ pressure over a short pipe length and decelerates much faster. At 12 m/s2 the dual-disc figure rises to about 0.3 m/s (3.9 bar), so model that duty and lean towards a nozzle or silent check.
- Full opening. Compare 1.86 and 0.93 m/s with the full-open velocity on each data sheet. If turndown falls short, the plates hang part-open and wear; an NPS 6 valve (ID 154.1 mm) would run 3.2 and 1.6 m/s, with more pressure drop.
Sizing for Full Opening and Pressure Drop
Swing and dual-plate checks need a minimum velocity to open fully. Below it the disc floats, chatters and wears, and since a part-open valve has a lower Cv than its catalogue value, the real pressure drop is higher than calculated (Valve Magazine, 2025). Size for the flow, not the line, check the lowest controlled flow, and compare certified Cv or Kv at equal flow using our Cv and Kv pressure drop guide.
Installation Details That Decide Service Life
- Straight run. Installation manuals typically ask for 5 pipe diameters after an elbow, tee, pump or valve, and about 2 after the check valve.
- Orientation. In horizontal pipe, set the dual-plate hinge pin vertical so gravity acts equally on both plates; in vertical pipe, use upward flow unless the manufacturer approves down-flow in writing.
- Plate clearance. Open plates project past the wafer face, so a butterfly valve bolted to the outlet, lined or heavy-wall pipe, or a reducer can block them.
- Flammable service. Long, exposed wafer through-bolts can stretch in a fire and leak at both gaskets; the AIChE CCPS Process Safety Beacon calls fully flanged valves the inherently safer solution. Use double-flanged or lug bodies on hydrocarbon and LPG lines.
- Debris. Weld slag between the plates holds the valve open; fit an upstream strainer.
Canadian Approvals and the Submittal Package
CRN under CSA B51
In Ontario, the TSSA fitting registration guideline requires fittings in pressure-retaining systems designed above 15 psi to be registered, subject to the regulation’s exemptions. Valves are Category C fittings under CSA B51:24 Table 1, registered in the manufacturer’s name; one made outside Canada is registered first in the province of first use. Ask for the CRN with the submittal, check that its scope covers your size, class and material, and find it on the valve (category letter C; a 5 after the decimal point shows Ontario registration). Other provinces apply CSA B51 through their own regulators.
Fire protection and potable water
Check valves in sprinkler, standpipe and fire pump systems must be listed for fire-protection service. The binational standard behind that listing is ANSI/CAN/UL/ULC 312 (NPS 1 and up), which in Canada is written for use with the National Fire Code and National Building Code; insurers often want FM approval too. An industrial wafer check is no substitute; see our fire protection check valves. For domestic water, ask for NSF/ANSI/CAN 61 and 372 certification.
Standards to check on the data sheet
- API 594: wafer, lug and double-flanged single-plate, dual-plate and pivoting-disc valves (Type A) and flanged or butt-welding valves (Type B). The tenth edition appeared in September 2026; agree which edition governs. Axial-disc, center-guided, nozzle and lift checks are excluded.
- MSS SP-125 (iron) and SP-126 (steel and alloys): in-line, spring-loaded, center-guided silent checks.
- AWWA C518: double-disc swing-check valves for waterworks, NPS 2 to 48.
- API 598 testing, with EN 10204 3.1 material certificates for steel valves.
Watch for a center-guided silent check offered “to API 594”, which excludes it, and for a CRN whose scope stops short of the size or class supplied. On multi-pump or high-head duties, ask for the dynamic characteristic curve; without it, the slam check is guesswork.
Selection Checklist
- Define the duty: fluid, temperature, pressure class, and flow at design and at minimum controlled operation.
- Identify the worst stop (power failure, or one pump tripping while others run); model multi-pump systems.
- Convert each candidate’s reverse velocity to surge with ΔP = ρ × a × Vr.
- Confirm full opening at design and minimum flow, and compare certified Cv or Kv at equal flow.
- Choose the body: wafer for clean, low-risk service; lug or double-flanged for flammable lines; retainerless where body penetrations are unacceptable.
- Confirm orientation, straight runs and plate clearance.
- Collect the paperwork: CRN for the exact size and class, ULC/UL 312 and FM for fire service, NSF/ANSI/CAN 61 and 372 for potable water, the API 594 edition, and test and material certificates.
- Fit an upstream strainer where debris is possible.
Get a Check Valve Recommendation
ValveAtlas (ValveAtlas Industrial Solutions) supplies industrial check valves across Canada and the United States, including dual plate wafer check valves in wafer, lug and double-flanged, retained or retainerless designs. Send us the pump curve, static head, line length and pipe material, and we will return a recommendation and a submittal package that answers the questions above.
Request a quotation or a technical review:
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Email: info@valve-atlas.com
Phone: +1 (647) 553-7109
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