Pressure Seal Valves



Steel, Stainless Steel, Monel, Hastelloy, Duplex, Super Duplex


Flanged, Welded Mouth

Drive Unit:

Manual, Electric, Pneumatic, Hydraulic


max.(+550 °C)

Nominal Diameter:

2″ – 16″

Rated Pressure:

Class 600 – 2500

Pressure Seal Valves

Pressure seal construction is adopted for Valves for high pressure service, typically in excess of above 170 bar. The unique feature about the pressure seal Bonnet is that the body-Bonnet joints seals improves as the internal pressure in the Valve increases, compared to other constructions where the increase in internal pressure tends to create leaks in the body-Bonnet joint.


Bolted Bonnets vs. Pressure Seals

To better understand the pressure seal design concept, let’s contrast the body-to-Bonnet sealing mechanism between bolted Bonnets and pressure seals. FIG. 1 depicts the typical Bolted Bonnet valve. The body flange and Bonnet flange are joined by studs and nuts, with a gasket of suitable design/material inserted between the flange faces to facilitate sealing. Studs/nuts/bolts are tightened to prescribed torques in a pattern defined by the manufacturer to affect optimal sealing. However, as system pressure increases, the potential for leakage through the body/Bonnet joint also increases.

Now let’s look at the pressure seal joint detailed in FIG. 2 Note the differences in the respective body/Bonnet joint configurations. Most pressure seal designs incorporate “Bonnet take-up bolts” to pull the Bonnet up and seal against the pressure seal gasket. This in turn creates a seal between the gasket and the inner dia (I.D.) of the valve body.





A segmented thrust ring maintains the load. The beauty of the pressure seal design is that as system pressure builds, so does the load on the Bonnet and, correspondingly, the pressure seal gasket. Therefore, in pressure seal Valves, as system pressure increases, the potential for leakage through the body/Bonnet joint decreases.

This design approach has distinct advantages over bolted Bonnet Valves in main steam, feedwater, turbine bypass, and other power plant systems requiring Valves that can handle the challenges inherent in high-pressure and temperature applications.




  • Pressure Seal Gate Valve
  • Pressure Seal Globe Valve
  • Pressure Seal Check Valve



  1. No pressure retaining body-bonnet flanges or bolting.
  2. Forged structure for all pressure containing parts. Optimized design for thermal fatigue required for power plant where frequent start-ups & shut-downs are the must.
  3. Flanged valves are provided with flanges integral to the valve body forging or full penetration welded.
  4. Lighter weight design compared to bolted bonnet.
    5. High quality packing for reliable tightness and low emission performance.
  5. Sealing surface sare machined to the tightest tolerances and lowest roughness and to ensure reliable sealing & long service life.
  6. High Class CV values.
  7. OutsideScrewandYoke(OS&Y).
  8. Low operation torque design.
  9. Self aligning two piece packing gland.
  10. Graphite based Pressure seal gasket with metal anti- extrusion caps.