A stainless check valve is a self-acting valve: forward flow lifts a closure off its seat, and gravity, a spring or the reverse flow itself puts it back. The British and Middle Eastern phrasing is non-return valve, and the two are the same device. Stainless is the material decision and it is the least interesting of the four decisions on the page, because it changes what the valve survives rather than how it works.
The other three are where specifications go wrong. The closure - swing, dual plate, single plate, lift or piston - decides how fast the valve reacts to a reversal, which decides the surge pressure, and it also decides which installation positions are legal. The standard decides which sizes and end connections the valve can legally be built in at all. The seat decides whether you get zero leakage at a temperature ceiling or a defined allowance at full temperature. A data sheet that says only stainless steel check valve, NPS 4, Class 150 has answered none of them.
Design standard
| Item | Standard |
|---|---|
| Basic Design | API603/B16.34 |
| Face to Face/End to End | ASME B16.10 |
| End Flange | ASME B16.5 |
| Butt-welding End | ASME B16.25 |
| Pressure-temperature Rating | ASME B16.34 |
| Inspection and Testing | API 598 |
Design Features
1. Optional swing or lift type of disc.
2. Optional anti-rotation disc.
3. Integral metal seat to ensure abrasion-resistance, a reliable sealing and and longer service life.
4. Internal design of hinge pin connecting with hinge to avoid externalleakage and ensure reliability in service.
Stainless Steel Check Valve drawing
Material of Construction
| Part No. | Part Name | Material |
|---|---|---|
| 1 | Body | ASTM A351 GR.CF8M +HF |
| 2 | Disc | ASTM A351 GR.CF8M +HF |
| 3 | Disc Lock Nut | ASTM A276 Type 316 |
| 4 | Hinge | ASTM A351 GR.CF8M |
| 5 | Hinge Pin | ASTM A276 Type 316 |
| 6 | Gasket | PTFE |
| 7 | Cover | ASTM A351 GR.CF8M |
| 8 | Stud | ASTM A193 GR.B8 |
| 9 | Nut | ASTM A194 GR.8 |
Dimension & Weight
Class 150
| Size | L-RF/BW | L-RTJ | H | Approx Weight | |||||
|---|---|---|---|---|---|---|---|---|---|
| NPS | DN | mm | in | mm | in | mm | in | kg | lb |
| 2 | 50 | 203 | 8.00 | 216 | 8.50 | 126 | 4.96 | 12 | 25 |
| 2 1/2 | 65 | 216 | 8.50 | 229 | 9.00 | 142 | 5.59 | 16 | 35 |
| 3 | 80 | 241 | 9.50 | 254 | 10.00 | 149 | 5.87 | 19 | 41 |
| 4 | 100 | 292 | 11.50 | 305 | 12.00 | 165 | 6.50 | 34 | 75 |
| 6 | 150 | 356 | 14.00 | 368 | 14.50 | 208 | 8.19 | 59 | 130 |
| 8 | 200 | 495 | 19.50 | 508 | 20.00 | 257 | 10.12 | 113 | 249 |
| 10 | 250 | 622 | 24.50 | 635 | 25.00 | 359 | 14.13 | 221 | 487 |
| 12 | 300 | 699 | 27.50 | 711 | 28.00 | 397 | 15.63 | 320 | 705 |
Class 300
| Size | L-RF/BW | L-RTJ | H | Approx Weight | |||||
|---|---|---|---|---|---|---|---|---|---|
| NPS | DN | mm | in | mm | in | mm | in | kg | lb |
| 2 | 50 | 267 | 10.50 | 283 | 11.12 | 127 | 5.00 | 14 | 31 |
| 2 1/2 | 65 | 292 | 11.50 | 308 | 12.12 | 142 | 5.59 | 22 | 49 |
| 3 | 80 | 318 | 12.50 | 333 | 13.12 | 149 | 5.87 | 36 | 79 |
| 4 | 100 | 356 | 14.00 | 371 | 14.62 | 164 | 6.46 | 46 | 100 |
| 6 | 150 | 445 | 17.50 | 460 | 18.12 | 218 | 8.58 | 88 | 194 |
| 8 | 200 | 533 | 21.00 | 549 | 21.62 | 273 | 10.75 | 180 | 397 |
| 10 | 250 | 622 | 24.50 | 638 | 25.12 | 388 | 15.28 | 289 | 637 |
Valve factory
To quote accurately we need nine things: pattern, nominal size, pressure class, body and trim material, seat type, end connection, medium and concentration, design temperature and pressure, and installation orientation. The two that are most often missing are the minimum and maximum flow rate, which decides whether the valve will flutter, and the orientation, which rules out patterns before price is even discussed. Send those with the data sheet and the quotation comes back with a recommendation rather than a number.
FAQ
Is a stainless steel check valve the same as a non-return valve?
Yes. Non-return valve, one-way valve and check valve are three names for one device: a valve that opens on forward flow and closes when flow stops or reverses, with no operator and no actuator. The naming difference is regional rather than technical, and both appear on the same purchase orders. What the name does not tell you is which closure the valve uses, which standard it is built to, or what its seat is made of, and those three decide whether it works in your line.
Which standard applies to a stainless steel check valve?
It depends on size, class and end connection, and no single standard covers all three. API 594 covers wafer, lug, double flanged and bolted cover swing checks from NPS 2 upward to Class 2500. API 602 covers forged checks from NPS 1/4 to 4 including threaded and socket weld ends. MSS SP-42 covers corrosion resistant lift, swing and Y-pattern checks from NPS 1/2 to 24 in Class 150 to 600, with flanged and butt weld ends only. BS EN 16767 covers metallic checks from DN 8 to 1200. Below NPS 2 with a threaded end, API 594 is not available to you.
Can a check valve below NPS 2 be certified to API 594?
No. The smallest size in API 594 is NPS 2, for both the short pattern type and the long pattern type, at every pressure class. A supplier who lists a quarter inch or one inch valve against API 594 is describing a size the standard does not contain. For those sizes the correct references are API 602 for a forged valve, which starts at NPS 1/4 and includes threaded and socket weld ends, or BS EN 16767, which covers socket weld and threaded ends up to DN 65.
Why is a metal seated check valve allowed to leak more than a gate valve?
Because nothing forces the disc onto its seat. API 598 permits a metal seated check valve to pass three times its nominal size in cubic centimetres per minute; a metal seated gate valve of the same size is allowed two drops per minute for every nominal size, which works out at one eighth of a cubic centimetre per nominal size. The ratio is 24 at every size. It is not a quality concession, it is the geometry: the check closes on gravity and reverse flow alone, while the gate is pulled shut by an operator applying torque.
How do I size a check valve?
By flow velocity, not by line size. A swing check needs roughly 1.4 to 2.2 metres per second of liquid to hold the disc fully open, and the empirical figure for water at 20 degrees is 1.42. Below that the disc hovers part open, sheds vortices and hammers against its own hinge, and the hinge pin wears oval within months. An oversized check valve is therefore worse than an undersized one, which is the opposite of the rule most buyers apply.
Can a stainless steel check valve be installed vertically?
It depends on the type, and vertical downward flow is refused by most of them. A swing check works in a horizontal line or in a vertical line with upward flow, where the disc weight then works against opening and the minimum velocity rises. A lift or piston check needs a horizontal line or vertical upward flow. A dual plate or spring loaded wafer check closes on spring force and can be fitted in any of the three positions. Installing a swing check in downward flow leaves the disc hanging open and it slams on the first reversal.
Why does my check valve chatter?
Almost always because the flow is too low for the valve, which in practice means the valve is too big. The disc sits in a partly open position where the flow separates off its trailing edge, and it oscillates at high frequency against the seat and the hinge. The damage is mechanical rather than corrosive: peened hinge pin ends, impact craters on the seat face, and eventually a fatigue crack in the pipe weld at the valve. A smaller valve, a reduced bore, or a spring assisted dual plate in the same space fixes it.
What is cracking pressure and why does it matter?
It is the differential pressure at which the disc first lifts. A swing check needs only a few centimetres of water column, around 7 to 35 millibar, so it costs almost nothing in head but also seals weakly against a low reverse pressure. A spring loaded check typically cracks at 0.05 to 0.5 bar and can be built to about 1.7 bar, and that cracking pressure is a permanent loss you pay for on every hour of pumping. On a low head circulating duty, that loss is the whole selection.
Will a swing check valve drop into the space a gate valve came out of?
No. At Class 150 and NPS 6 a gate valve is 267 mm face to face and a swing check is 356 mm, so the check is 89 mm longer and the spool has to be cut. A wafer dual plate in the same size is 98 mm, which is 258 mm shorter than the swing check. Check valve types are not dimensionally interchangeable with each other or with gate valves, and a change of type always means new pipe, new supports and a revised isometric.
Does a soft seat solve the leakage problem?
For leakage yes, for temperature no. A resilient seat is required to show zero leakage in both the water and the air seat test at any size, which is what a pump discharge or a dosing line usually needs. The price is a ceiling around 200 degrees for a PTFE insert and about 250 for PEEK, whatever the CF8M body is rated to. Above that ceiling the insert is the limit, and the valve goes back to a metal seat and the API 598 allowance.
Why did the hinge pin seize on a stainless valve?
Crevice corrosion, not galling. Stainless steel needs oxygen to rebuild its passive film, and the clearance between the hinge pin and its bore is too narrow for the medium to circulate, so the oxygen inside is consumed and never replaced. In ambient seawater a 316 crevice corrodes at any gap narrower than 0.4 mm, and a 304 crevice at any gap narrower than 0.9 mm. A seized pin leaves the valve either stuck open, so it protects nothing, or stuck shut, so it blocks the line.
What documents come with the valves?
An EN 10204 3.1 inspection certificate with the heat number traceable to the body casting, a pressure test report for each valve giving the shell and seat pressures and the hold times, a dimensional report, and a certificate of conformity. EN 10204 3.2 with an independent inspector signing is available, and PMI, radiography and penetrant testing on the castings can be added. Where the specification calls for a third party witness, book it at production stage rather than after packing.
What is the minimum order quantity and lead time?
One piece for a stock size. Standard CF8 and CF8M sizes in Class 150 and 300 in wafer and swing patterns ship in about seven days from stock. Made to order valves are 20 to 25 days from drawing approval, and a valve with a soft seat, a special trim or a NACE requirement is quoted with a firm date rather than a range.
What is the warranty, and can you supply under our brand?
18 months from shipment against defects in material and workmanship. Wear parts are the seat insert on a soft seated valve, the hinge pin and the gasket, all three available as spares with the original heat number. OEM nameplates, your tag numbers and your painting system are all possible. What we will not do is stamp a standard we have not tested to: every valve is designed and tested to API 594 or MSS SP-42 as applicable, and we do not claim an API Monogram.