Dual Plate Wafer Check Valve — API 594 Engineering Guide
Technical reference · Supreme Valves India · June 2026 · 18 min read
The dual plate wafer check valve (also called a twin-disc or double-door check) is the most space-efficient non-return valve for ANSI/ASME flanged piping from 2" through 60". This guide consolidates design, material, dimensional, and procurement data aligned with API 594 and ASME B16.34, as applied to Supreme Valves dual plate wafer and lug check valves.
1. Purpose and operating principle
Dual plate check valves allow flow in one direction only. Forward pressure lifts two half-discs on a central hinge pin; springs (Inconel X-750 on standard carbon builds) return the discs to the flat seat as flow slows, typically before reverse flow establishes—giving fast, low-noise closure compared to swing checks.
2. Applicable standards
| Standard | Application |
|---|---|
| API 594 | Design, end-to-end dimensions, wafer/lug/double-flange configurations |
| API 598 | Shell and seat testing (1.5× and 1.1× rated pressure) |
| ASME B16.34 | Pressure-temperature ratings by body material |
| ASME B16.5 / B16.47 | Flange dimensions (RF, RTJ; large bore) |
| NACE MR0175 | Sour service material limits (on request) |
3. Internal construction (typical WCB build)
| # | Component | ASTM (typical) | Function |
|---|---|---|---|
| 1 | Body | A216 WCB | Wafer or lug shell; ~10% lighter than flanged swing check |
| 2 | Seat | WCB + 410 overlay or soft insert | Flat seat — avoids board-snap failures |
| 3 | Discs (×2) | A351 CF8 (trim W1) | Half-plates on hinge pin |
| 4 | Spring(s) | Inconel X-750 | Single: 2"–6"; double: ≥8" |
| 5–6 | Shaft, stop pin | A276 Gr. 410 | Stop pin limits over-travel |
| 7–8 | Shaft support, retainer | A276 Gr. 410 | Hermetic — no through-body holes |
4. Trim codes W1–W6
| Trim | Discs | Pin / stop pin | Typical service |
|---|---|---|---|
| W1 | CF8 | 410 | General water, oil, air |
| W2 | CF8 | F304 | Improved corrosion on pins |
| W3 | CF8M | F316 | Seawater, mild chlorides |
| W4 | CF3 | F304L | Low-carbon, welded systems |
| W5 | CF3M | F316L | Acetic acid, sea water, steam |
| W6 | CD3MN | F51 | Duplex, chloride service |
5. Body materials (selection summary)
| Casting | Service | Temperature (indicative) |
|---|---|---|
| A216 WCB / WCC | Water, oil, gas — non-corrosive | −20°F to +800°F |
| A217 WC6 / WC9 | Elevated temperature hydrocarbons | to +1100°F |
| A352 LCB / LCC | Cryogenic / low temp | to −50°F (max +650°F LCB) |
| A351 CF8 / CF8M | Corrosive or high-temp oxidizing | −450°F to +1200°F |
6. Soft seat temperature limits
| Elastomer | Range |
|---|---|
| Buna-N | −60°F to 250°F |
| Viton | −10°F to 400°F |
| EPDM | 0°F to 300°F |
| Neoprene | 0°F to 212°F |
| Metal-to-metal | Per B16.34 for body grade |
7. Size and class availability
Dual plate valves are offered from 2" to 60" in classes 150, 300, 600, 900, 1500, and 2500 (RF/RTJ/PN). Not every NPS is available in every class at the top of the range—for example, Class 2500 is generally limited to smaller bore sizes. Confirm the matrix on your datasheet or RFQ.
8. Face-to-face dimensions (Class 150 sample)
Dimension L is the face-to-face installed between flanges (mm).
| NPS | DN | L | Port D | Weight kg |
|---|---|---|---|---|
| 2 | 50 | 60 | 51 | 2 |
| 6 | 150 | 98 | 152 | 13 |
| 12 | 300 | 181 | 305 | 54 |
| 24 | 600 | 222 | 600 | 331 |
| 48 | 1200 | 524 | 1166 | 1450 |
Class 300 L values are similar on smaller sizes but increase on large NPS; see full tables in the technical datasheet.
9. Pressure-temperature (WCB, psig)
| °F | Class 150 | 300 | 600 | 900 |
|---|---|---|---|---|
| 100 | 285 | 740 | 1480 | 2220 |
| 400 | 200 | 635 | 1265 | 1900 |
| 600 | 140 | 570 | 1135 | 1705 |
10. Pressure drop at 10 ft/s water
At 3.048 m/s (10 ft/s) water at ~60°F, indicative pressure loss decreases as size increases:
| NPS | ΔP (psi) | Head loss (ft) |
|---|---|---|
| 2 | 4.55 | 10.5 |
| 8 | 1.21 | 2.8 |
| 12 | 0.825 | 1.9 |
| 24 | 0.424 | 0.98 |
11. Wafer (H) vs lug (L) vs double flange (D)
- H — Wafer: Lowest weight; bolts clamp valve between flanges. Best for inline installation where both flanges can be spread.
- L — Lug: Dead-end service; downstream flange removal for isolation. See lug type product page.
- D — Double flange: From 12" where bolting pattern requires flanged valve body ends.
12. Ordering example
24" H 6 S P F W1 = 24" NPS, wafer, Class 600, WCB body, metal seat, RF/serrated face, trim W1.
Replace H with L for lug, 6 with pressure class digit (1=150, 3=300, etc.), and seat code per datasheet (E=EPDM, V=Viton, …).
13. Procurement checklist
- NPS, pressure class, flange standard (B16.5 vs B16.47 Series A/B)
- Body and trim (W1–W6), seat type (metal vs elastomer)
- Model H, L, or D; RF vs RTJ
- Test standard (API 598), NDE, PMI, NACE
- Stud length = upstream flange thickness + L + downstream thickness + nut allowance