Forged Steel Self-Sealing Wedge Gate Valve

Size: 2" - 12" (DN50 - DN300)

Pressure: Class 600 - 2500 / PN 100-420

Standard: API 602, ASME B16.34, manufacturer-specific for pressure-seal bonnet

Body Materials: A182 F22, A182 F91, A182 F316, A182 F304 (all forged)

Wedge: Flexible wedge

Bonnet: Pressure-seal (self-sealing)

Stem: OS&Y rising stem with handwheel

Ends: Butt weld or flanged

Two Things That Change Everything at High Pressure

This valve solves two problems that appear above Class 600 — problems that bolted-bonnet cast-body gate valves can't handle. First, the bonnet seal. Second, the body integrity. Together, they make this valve the standard specification for power station main steam, reheater isolations, high-pressure feedwater, and petrochemical high-pressure service where the operating conditions exceed what a standard gate valve can safely contain.

Pressure-Seal Bonnet — the Seal That Gets Stronger Under Pressure

At Class 150-300, a bolted bonnet works fine. The internal pressure pushes the bonnet upward, and the bonnet bolts hold it down against the gasket. Manageable forces, reasonable bolt sizes, straightforward assembly. At Class 600 and above, the upward force on the bonnet becomes enormous. The bolts have to be massive — think 2-inch-diameter studs with hydraulically tensioned nuts on Class 1500 and 2500 valves. That hardware is expensive, difficult to torque correctly in the field, and creates maintenance problems every time you need to disassemble the valve.

The pressure-seal bonnet eliminates the bolt problem entirely. Instead of bolts holding the bonnet against the body, the internal line pressure does the work. Inside the bonnet-to-body joint, a segmented seal ring sits between the bonnet skirt and the body bore. When pressure enters the valve, it pushes upward against the bonnet and simultaneously compresses the seal ring against the body wall. Higher pressure compresses the seal harder. At Class 2500 operating pressure, that seal ring is compressed so tightly between the bonnet and body that leakage through the joint becomes physically impossible — the pressure that could cause leakage is the same pressure that creates the sealing force.

The bonnet is held in position by a retaining ring or threaded connection, not by the bolts you see on the outside. Those bolts serve one purpose — low-pressure seating during startup when the line pressure hasn't reached the threshold where the seal ring compresses effectively. Once the valve is at operating pressure, those bolts are unloaded. They're not carrying the seal force. The line pressure is.

This design has a maintenance advantage that experienced valve technicians understand immediately — there are no gaskets to replace and no bolt torquing procedures to follow during reassembly. The seal ring is a metal component that gets inspected and re-lapped if needed. The bonnet re-installs by dropping it into the body bore and engaging the retaining ring. When pressure comes back up, the seal re-establishes itself automatically.

Forged Body — No Porosity, No Leaks at Class 2500

Cast valve bodies at Class 600 and below work reliably. The casting process produces sound metal with acceptable quality levels for those pressure ratings. But at Class 600-2500, casting porosity becomes a risk you can't accept. Castings can contain microscopic voids — trapped gas pockets, shrinkage cavities, inclusion defects — that are invisible on the surface but leak under sustained high-pressure loading. A porosity defect in a Class 2500 valve body wall would leak immediately when the valve goes into service. The wall thickness at those ratings is calculated with minimal margin — there's no extra metal to absorb a void.

Forging eliminates the porosity problem. The forging process compresses the metal under massive pressure, closing any voids and aligning the grain structure into a dense, uniform matrix. A forged body has no internal cavities, no gas porosity, no shrinkage defects. The metal is solid throughout the wall section. At Class 600-2500, that solid-body integrity is the reason forged construction is the standard — not an upgrade option, but the baseline requirement.

The forged alloys for this valve are selected for their specific service conditions. A182 F22 (2.25% Cr-1% Mo) for high-temperature service where creep resistance matters. A182 F91 (9% Cr-1% Mo-V) for the highest temperature applications — main steam and reheater lines in power stations operating at 1000°F and above. The vanadium addition in F91 provides superior long-term creep strength compared to F22. A182 F316 and F304 for corrosive service where the stainless chemistry resists the process fluid attack.

Flexible Wedge — Required at These Temperatures

At Class 600-2500, the operating temperatures are high enough that thermal expansion binding is a certainty with a solid wedge — not a possibility, a certainty. The flexible wedge with its central hub and deflectable wings prevents that binding. Each wing adjusts independently to the seat ring expansion, maintaining contact across both seats regardless of asymmetric heating or differential expansion rates. At these pressure and temperature levels, the flexible wedge isn't an optional upgrade. It's the only wedge design that works.

A: Bolted bonnets at Class 600+ require massive studs to hold the bonnet against internal pressure — expensive hardware that's difficult to torque and maintain. Pressure-seal bonnets use line pressure itself as the sealing force. Higher pressure creates a tighter seal. No gasket replacement, no bolt torquing, and the seal self-adjusts to operating pressure.

A: The external bonnet bolts provide low-pressure seating during startup or when line pressure is below the effective sealing threshold. Once operating pressure is established, the pressure-seal ring takes over. The bolts are unloaded at operating pressure.

A: Castings can contain microscopic porosity — voids that leak under sustained high pressure. Forging compresses the metal into a solid, void-free matrix. At Class 600-2500, a porosity defect in the body wall would leak immediately. Forged construction eliminates that risk entirely.

A: F91 for operating temperatures above 900°F where long-term creep resistance is critical — main steam and reheater service in power stations. F22 for moderate high-temperature service up to about 800°F. The vanadium addition in F91 provides significantly better creep strength at the highest temperatures.

A: Yes. The pressure-seal bonnet design allows in-line maintenance — the bonnet can be removed for internal access without cutting the valve out of the piping. The seal ring is re-usable after inspection and re-lapping. No gasket replacement required during reassembly.