A swing check valve closes on gravity and reverse flow, so its clapper can land after the column has already reversed. A silent check valve - the trade name for a spring, non-slam or axial-flow check valve - closes the disc on a short spring stroke before reverse flow develops. That one difference decides the selection.
Both valves are non-return valves, and both prevent backflow; the difference is what closes the disc and when. A swing check valve uses a hinged clapper that opens on forward flow and falls back under gravity once flow stops, so it cannot begin to close until the column has slowed or reversed. A silent check valve - the common trade name for a spring check valve, also sold as a non-slam check valve - holds the disc closed with a spring and drives it onto the seat over a short stroke while forward velocity is still decaying. Within that family the axial-flow check valve, also called the nozzle check valve, is the most effective construction. This page compares them on closing speed, head loss, orientation, standards and sizing.
Technical Specifications
The two designs are compared line by line below, then summarised in a supply range and a selection table. Confirm face-to-face against ASME B16.10 and the flange drilling against ASME B16.5 or EN 1092 before ordering.
| Parameter | Swing check valve | Silent check valve |
|---|---|---|
| Closing mechanism | Hinged clapper; gravity and reverse flow | Spring-loaded centre-guided disc or poppet |
| Closing time | ≈ 200 ms to 2 s (slam-prone) | ≈ 20–80 ms; often under 0.1 s |
| Water hammer risk | High in fast-reversing service | Very low; seats before reversal |
| Cracking pressure | 0.1–0.5 psi (gravity) | 0.5–25 psi (spring set) |
| Loss coefficient K | 0.6–1.5 (lowest) | 2–10 spring lift; 0.5–1.2 axial nozzle |
| Installation orientation | Horizontal, or vertical with upward flow | Any orientation, up-flow or down-flow |
| Typical size range | DN50–DN1200 (NPS 2–48) | DN50–DN600; axial nozzle to DN1200 |
| Pressure class | Class 150–2500 | Class 150–2500 |
| Solids / slurry tolerance | Good - unobstructed bore | Poor - spring and guides foul |
| Relative cost (same size) | Baseline (lowest) | 1.5–3× swing |
| Closure wear | Seat and hinge impact each cycle | Low impact; ages through the spring |
| Size range | DN50–DN1200 (NPS 2–48); inline spring checks DN15–DN40 |
|---|---|
| Pressure class | Class 150–2500 (ASME B16.34); PN10–PN40 |
| Design standards | API 594 check valve (Type A wafer / lug / dual-plate; Type B long-pattern swing), API 6D check valve for pipeline service, AWWA C508 iron-body swing, BS 1868 / BS 5153 |
| End connections | Wafer, lug, double-flanged RF/RTJ, butt-weld (ASME B16.25) |
| Face-to-face | ASME B16.10 / API 594 short pattern |
| Test standard | API 598 (shell and seat), ISO 5208 leakage rates, EN 12266-1 |
| Temperature range | −46 °C to +425 °C, depending on body and seat material |
| Body materials | ASTM A216 WCB, A105, A352 LCB, ASTM A351 CF8M; ductile iron GJS-400-18 (GGG-40) |
| Springs | 304 / 316 SS; Inconel X-750 for high-cycle or high-temperature service |
| Certification | MTC to EN 10204 3.1 as standard, 3.2 on request; NACE MR0175 / ISO 15156 option |
| Commercial | MOQ 1 pc; lead time 4–8 weeks; warranty 18 months |
Seat leakage: what the standards actually allow
A check valve is not a shut-off valve, and the standards say so by grading check valves to a looser leakage class than other valve types. This is the single most misrepresented point in supplier literature, for both swing and silent designs.
| Standard | Other valve types | Check valves |
|---|---|---|
| ISO 5208 | Rate A / AA / CC depending on seat and fluid | Rate G (liquid) and Rate EE (gas) - the two loosest rates |
| API 6D | Rate D (liquid and gas) | Rate G (liquid) and Rate EE (gas) |
| API 598 | Metal-seated table in drops/min and bubbles/min | Separate check-valve table in cm³/min and m³/min |
| MSS SP-61 | Base table per NPS/DN | May take up to four times the base-table rate |
| ANSI/FCI 70-2 | Class II–VI (control valves) | Not applicable - not intended for check valves |
Note: Because a check valve's task is to limit backflow rather than to seal tight, "zero leakage" or "Class VI per API 598" has no basis for this valve type. Specify the leakage class the product standard assigns, and state the standard and edition on the order.
Selection guide
| Primary concern | Choose | Why |
|---|---|---|
| Lowest head loss on a large, steady line | Swing check valve | Unobstructed bore, K 0.6–1.5 |
| Fast flow reversal, pump trip | Silent check valve | Closes in 20–80 ms, before reversal |
| Vertical line with downward flow | Silent check valve | Spring-driven closure, gravity-independent |
| Solids, slurry or fibrous media | Swing check valve | Unobstructed bore does not foul |
| Tight face-to-face, retrofit | Silent (dual-plate / wafer) | API 594 Type A short pattern |
| Low cracking pressure, gravity line | Swing check valve | Opens at 0.1–0.5 psi |
| Low-noise requirement | Silent check valve | Soft, impact-free seating |
| High-velocity steam or gas, low loss needed | Tilting disc check valve | Short stroke, low loss without slam |
Why Source Swing and Silent Check Valves From Us
Application-first selection: We recommend swing or silent from your closing time, head loss and media rather than from stock, so the valve matches the reversal the line can actually produce.
Standard discipline: Every offer names the design standard, the test standard, the edition and the leakage class that applies to a check valve, so the acceptance criteria on the certificate can be checked against the specification.
Testing on every unit: Shell and seat tests to API 598 are run on each valve with the report supplied; positive material identification and NACE MR0175 / ISO 15156 options are available for sour and critical service.
test and inspection
Send your valve type, size, pressure class, body material, cracking pressure, flow rate, and installation orientation - our technical team will confirm the specification and return a quotation with lead time. Contact GNEE or email our team for valve and piping packages.
FAQ
What is the difference between a swing check valve and a silent check valve?
The difference is what closes the disc and when. A swing check valve relies on gravity and reverse flow, closing in about 200 ms to 2 s and often after the column has reversed. A silent check valve uses a spring to close the disc in roughly 20–80 ms, before reverse flow develops, which removes the water-hammer surge. Silent, non-slam, spring and axial-flow are trade names for the same family.
Which check valve stops water hammer?
The silent check valve. Because the surge follows ΔP = ρ·a·ΔV, it scales with the reverse velocity at closure. A spring-loaded disc seats while forward flow is still decaying, so reverse velocity stays near zero and the spike is not generated. A swing check closes after reversal, which is when the pressure spike occurs.
What is the closing time of each type?
A swing check valve closes in roughly 200 ms to 2 s depending on size and velocity. A silent check valve closes in about 20–80 ms, often under 0.1 s, because the disc moves a short axial stroke under spring force rather than a long hinge arc.
Can both be installed vertically?
A swing check valve cannot be installed in a vertical line with downward flow, because gravity holds the clapper off the seat. In a vertical line it needs upward flow, and in horizontal pipe it will not seal against down-flow. A spring-loaded, dual-plate or axial-flow silent check valve works in any orientation.
What is the pressure drop difference?
Head loss follows hL = K·v²/2g. A full-bore swing check has the lowest loss coefficient, about 0.6–1.5. A lift check valve is highest at 2–10, and a dual-plate check valve falls between at 0.8–2. An axial-flow nozzle check valve sits at 0.5–1.2, because its venturi body recovers pressure downstream of the disc.
What seat leakage class applies to check valves?
Check valves are graded to the loosest classes: ISO 5208 Rate G for liquid and Rate EE for gas, which API 6D adopts, and MSS SP-61 permits up to four times its base rate. ANSI/FCI 70-2 Class II–VI does not apply to check valves. Neither type is a bubble-tight isolation valve.
What size, class and materials do you supply?
DN50–DN1200 (NPS 2–48) swing and axial-flow checks, and DN15–DN40 inline spring checks, in Class 150–2500 and PN10–PN40. Bodies include ASTM A216 WCB, A105, A352 LCB and ASTM A351 CF8M, with 304 / 316 or Inconel X-750 springs and metal or resilient seats.
What is the MOQ and lead time, and can you supply OEM?
The minimum order quantity is one piece, and a sample valve can be supplied for evaluation. Standard lead time is four to eight weeks depending on size, class and material. We produce to customer drawings and nameplates, and every unit is pressure-tested to API 598 before dispatch.