Pressure Seal Swing Check Valve

A pressure seal check valve with a swing disc is a high pressure swing check valve whose cover is held by line pressure rather than by stud preload, built in NPS 2 to 24 from Class 600 to 1500 and to NPS 12 at Class 2500, with butt weld or RTJ ends. Those two limits are not a catalogue habit: they are where the MSS SP-144 bonnet range and the API 594 Type B body range stop overlapping, and the arithmetic is set out below. What most orders get wrong is neither the class nor the size but the assumption that the bonnet is the decision - on a swing check valve the bonnet only decides how the cover is held, while the disc decides whether the valve works at all.

Design Standard

Design features

1. Segmental thrust ring absorbs the outward thrust along the stem generated by the intermal pressure.
2. Thrust rings to prevent deformation of the gaskets.
3. Stainless steel internals to ensure soundness and corrosion-resistance in the vital body sealing zone for carbon and alloy steel valves.
4. Soft steel gasket seal to provide large contact area for a perfect sealing.
5. Internal hinge pin design to avoid external leakage.
6. A hinge and hinge pin provided and mounted internally so as to permit full movement of the disc.
7. By-pass and drain valve are available when required 

Pressure Seal Swing Check Valve drawing

Material of Construction

Dimension & Weight

CLASS 600

CLASS 900

CLASS 1500

CLASS 2500

Valve Factory

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FAQ

What is a pressure seal swing check valve?

A swing check valve whose body-to-cover joint is sealed by line pressure instead of stud preload. The disc is hinged above the seat: forward flow lifts it, gravity and reverse flow return it. The bonnet is not bolted down; it sits in a tapered bore and internal pressure drives it into a graphite gasket held by a retaining ring, so sealing force rises with pressure. It is the same product that EN and BS vocabulary calls a pressure seal non-return valve.

What sizes and pressure classes can actually be supplied?

NPS 2 to 24 in Class 600, 900 and 1500, and NPS 2 to 12 in Class 2500. That is the overlap of two standards, not a capacity limit: MSS SP-144 covers pressure seal bonnets from NPS 2 to 50 in Class 600 to 4500, but API 594 Type B stops at NPS 24 for Class 150 to 1500 and at NPS 12 for Class 2500.

Is this an API 594 valve?

Only if you say which part of API 594 governs. API 594 defines Type B in its own scope as a bolted cover swing check, so a pressure seal bonnet falls outside that definition. The order should read API 594 for dimensions, ratings, examination and test, plus MSS SP-144 for the bonnet joint, which names API 594 as the parent standard for check valves.

What is the face-to-face dimension?

It comes from ASME B16.10, but not from a swing check column above Class 300. In Table 1.5-1 the header is Gate, Lift Check, Swing Check, Long Pattern, A and B; in Tables 1.5-3 and 1.5-4 it is Globe, Lift Check, and Swing Check. At long pattern the values are 559 mm at NPS 6 and 838 mm at NPS 12 in Class 600, 705 mm and 1130 mm in Class 1500, and 914 mm and 1422 mm in Class 2500.

How much leakage is allowed on the seat test?

For a metal seat, API 598 allows 3 x NPS cm³/min of water. That is 18 cm³/min at NPS 6, 36 at NPS 12 and 72 at NPS 24. A metal-seated gate valve of the same size is allowed 1.50 cm³/min at NPS 12, so the check valve allowance is 24 times larger at any size because both scale with NPS.

Can it be installed vertically?

In a vertical line only with upward flow, and in a horizontal line only with the cover up and the hinge axis horizontal. Vertical down-flow will leave the disc hanging off the seat, and the valve will pass reverse flow without ever appearing to fail.

What flow keeps the disc fully open?

The working rule is a minimum velocity of 45 times the square root of the specific volume in m3/kg. For water at 20 °C that is 1.42 m/s; for saturated steam at 40 bar it is about 10 m/s. Below it the disc flutters against the seat instead of standing open, and the wear shows up on the hinge pin and the seat face.

What temperature can it take?

It follows the body material, not the bonnet. A216 WCB is rated in ASME B16.34 Group 1.1 to 538 °C but is normally replaced above about 425 °C; A217 WC6 and WC9 run to 593 °C; A351 CF8M runs to 538 °C and down to −196 °C. In practice the die formed graphite gasket often sets the ceiling before the body does.

Can the gasket be reused?

No. It is coined into the body and bonnet tapers and cannot re-seat once disturbed, so every opening of the bonnet needs a new one, matched to that valve's actual taper dimensions rather than to its size and class. That is why a spare should be held per valve on critical duty and why lead time is measured in weeks.

How do I stop the valve slamming?

A pressure seal bonnet has no effect on closure speed. Damping is a separate option: a dashpot or air cushion, a lever and weight, or an external spring assists closure and slows the last part of the travel. If the surge matters, the fix is a surge analysis plus a damped swing check or a tilting disc design, not a heavier bonnet.

What documents come with the valve?

EN 10204 3.1 material certificates as standard and 3.2 when an independent inspector witnesses, shell and seat test reports to API 598 per serial number, a dimensional record against the drawing, positive material identification on alloy and stainless bodies, and marking to MSS SP-25.

What is the minimum order and lead time?

One piece, so a single valve can be bought for a maintenance job or for evaluation. Common sizes in A216 WCB and A217 WC6 ship in about 7 days from stock; Class 1500 and 2500 bodies and alloy grades run about 25 to 40 days plus transit from Tianjin.

Can you build to my drawing, and do you stamp API?

Drawings, OEM nameplates and project tagging are normal. What we do not do is claim an API Monogram: every valve is designed and tested to API 594 and MSS SP-144, and the marking says so, but a monogram requires a licence held by the manufacturing plant and we do not claim one.