Pressure Seal Gate Valve
gate · pressure seal bonnet
- Body
- A105, A182 F11, F22, F91, F92
- Size
- NPS 2-24 (DN 50-600)
- Class
- Class 600 - 4500
- Temp
- up to 650 °C / 1200 °F
- End
- BW, SW, RTJ, RF
- Standard
- ASME B16.34
Pressure seal valves
A pressure seal bonnet is a body-bonnet joint that uses line pressure to seal itself. The bonnet is inserted into the body from the inside, a tapered seal ring sits above it, and internal pressure pushes the assembly upward into the taper. The higher the pressure, the harder the joint seals. This is the opposite of how a bolted bonnet behaves, and it is the reason pressure seal construction dominates above roughly Class 900 in power service. Everything collected in this category uses that joint. Nothing else is admitted, because the term is worth nothing if it is applied loosely.
- Valve types
- Gate, globe, check, Y-globe stop check
- Bonnet design
- Self-energising pressure seal
- Pressure rating
- Class 900 - 4500
- Temperature
- to 650 °C
- Seal ring
- Flexible graphite, metal-lined
- End connection
- BW, RF, RTJ
What this category collects. Only products that demonstrably use a pressure seal bonnet or a self-energising centre-cavity joint are collected here. Bolted bonnet valves are excluded from this category even where they serve the same system.
Product range
Each entry below has one detail page, reached from every category that applies to it. The same valve is not published twice under different names.
Pressure Seal Globe Valve
globe · pressure seal bonnet
- Body
- A105, A182 F11, F22, F91, F92
- Size
- NPS 2-16 (DN 50-400)
- Class
- Class 900 - 4500
- Temp
- up to 650 °C / 1200 °F
- End
- BW, SW, RTJ, RF
- Standard
- ASME B16.34
Pressure Seal Check Valve
check · pressure seal bonnet
- Body
- A105, A182 F11, F22, F91, F92
- Size
- NPS 2-24 (DN 50-600)
- Class
- Class 600 - 4500
- Temp
- up to 650 °C / 1200 °F
- End
- BW, SW, RTJ, RF
- Standard
- ASME B16.34
Stop-Check Valve
stop check · pressure seal bonnet
- Body
- A182 F22, F91, F92
- Size
- NPS 2-16 (DN 50-400)
- Class
- Class 900 - 2500
- Temp
- up to 620 °C / 1148 °F
- End
- BW, RTJ, RF
- Standard
- ASME B16.34
Main Steam Valve
Gate / globe / check · pressure seal bonnet
- Body
- A182 F22, F91, F92
- Size
- NPS 2-24 (DN 50-600)
- Class
- Class 1500 - 4500
- Temp
- 540 - 650 °C for USC main steam
- End
- BW
- Standard
- ASME B16.34
Feedwater Valve
Gate / globe / check · pressure seal bonnet
- Body
- A105N, A182 F11, F22
- Size
- NPS 2-20 (DN 50-500)
- Class
- Class 1500, 2500
- Temp
- 150-300 °C typical
- End
- BW, RTJ, RF
- Standard
- ASME B16.34
How the joint works, and where it stops working
Working from the inside out: the bonnet passes up through the body neck and is lifted into position, a tapered graphite seal ring sits on the bonnet shoulder against a matching taper in the body bore, a thrust ring transmits load evenly into it, and split retainer segments in a groove take the upward load. Sealing force is proportional to line pressure. The consequence people miss is at the other end of the range: at very low pressure there is little force available to energise the seal, so initial tightness comes from assembly preload applied through the gland studs. A valve that weeps cold and seals perfectly hot is almost always an assembly problem, not a ring problem.
Design features
Self-energising joint
Sealing force rises with line pressure. No hot torquing, no re-tightening after the first thermal cycle, no gasket creep to compensate.
Segmental retainer
Split ring in a machined groove takes the upward load. Disassembly requires driving the bonnet down into the body first, which is the step crews familiar only with bolted bonnets get wrong.
Metal-lined graphite seal ring
Flexible graphite with a stainless or Inconel liner. Treated as a one-time part: a reused ring has taken a set and is a common cause of a valve that leaks after overhaul.
Compact envelope
No large bonnet flange, so the valve is lighter and shorter in the neck than an equivalent bolted design at the same class, which matters for pipe support loading.
Back seat on gate and globe
Allows the packing to be repacked under pressure where the specification and the operating procedure permit it.
Selection table
A first cut at gate, globe, check or stop-check. The values are catalogue ranges, not a commitment for a specific item.
| Product type | Body | Class | Temperature | Typical service |
|---|---|---|---|---|
| Pressure Seal Gate Valve | Cast or forged | 900 - 4500 | to about 650 °C | Full-bore isolation, main steam and feedwater |
| Pressure Seal Globe Valve | Forged | 900 - 4500 | to about 650 °C | Tight shut-off, drains and vents |
| Pressure Seal Swing Check Valve | Cast or forged | 900 - 2500 | to about 650 °C | Low-loss non-return, feedwater and steam |
| Pressure Seal Lift Check Valve | Forged | 900 - 2500 | to about 650 °C | Fast closure where reverse-flow stability matters |
| Y-Globe Stop Check Valve | Forged | 900 - 2500 | to about 620 °C | Boiler outlet, isolation plus non-return |
Materials
The grade is selected against the rating at your design temperature. The full matrix, with the reason each grade exists, is on the material matrix page.
| Material | Typical service | What decides whether it is right |
|---|---|---|
| A105 / F36 | General high-pressure steam and water | Forged carbon steel. Cheap and well understood, but it loses allowable stress quickly with temperature, so it has to be checked against the rating table rather than assumed. |
| F22 / WC9 | High-temperature steam | Chromium-molybdenum. The workhorse above the carbon steel limit, with useful creep strength and straightforward welding compared with the martensitic grades. |
| F91 / C12A | Supercritical steam | Modified 9Cr-1Mo. Much higher creep strength, but only if the heat treatment window was held. The furnace and PWHT charts are the evidence that it will perform, not the grade name. |
| F92 | Ultra-supercritical steam | Higher creep strength again at the top temperature and class combinations, with a narrower processing window than F91 and correspondingly less tolerance for error in heat treatment. |
| WB36 | High-pressure feedwater | High-strength low-alloy steel used where feedwater pressure rather than temperature governs, allowing a thinner wall than a carbon steel equivalent at the same class. |
| F347 | High-temperature corrosive media | Stabilised austenitic stainless. Selected for corrosion resistance and for stability against sensitisation, not primarily for creep strength. |
Applications
- Main steam and reheat isolation
- Boiler feedwater and feedwater heater isolation
- Turbine extraction and bypass
- Boiler drains, vents and blowdown
- High-pressure process steam in refining and coal chemical service
Standards and testing
Listed only where the standard actually governs something on these valves. What each one covers on a specific item is stated on that item's page.
Downloads
Catalogue, datasheets, material guide, pressure-temperature rating tables and the RFQ datasheet are collected in resources. Files carry a version date and use searchable text rather than scanned images.
Frequently asked questions
Does a pressure seal valve ever need re-tightening?
The body-bonnet joint should not. The gland does: packing consolidates during the first thermal cycles and the gland nuts are adjusted as part of commissioning. If the body-bonnet joint itself weeps in service, the cause is normally the seal ring, the taper surface or the assembly preload, not a torque figure that can be corrected by tightening something.
Can the bonnet be lifted out for maintenance?
No, and this is the most common damage mechanism at overhaul. The bonnet is larger than the bore it passes through when seated. It has to be driven down into the body to free the retainer segments, then the segments removed, then the bonnet withdrawn. Crews used to bolted bonnets try to lift it and damage the seal ring or the retainer groove.
Is a pressure seal valve suitable below Class 900?
It can be built, but it is usually the wrong answer. Below Class 900 a bolted bonnet is simpler to maintain and the pressure available to energise the seal is lower. We will say so rather than sell the more expensive construction.
Related
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