Pressure Seal Valves

In general, Pressure Seal Design is adopted for high pressure applications above 100 bar. The unique feature of the Pressure Seal Valve is that as the internal pressure inside the Valve increases, the sealing of the Body-to-Lid connection improves, compared to other structures where an increase in internal pressure tends to create leakage at the Body-to-Lid connection.

BOLTED and PRESSURE SEAL CONNECTIONS

To better understand the Pressure Seal design concept, let’s compare the Body-to-Cover sealing mechanism between Bolted Bonnets and Pressure Seal design, Figure 1 shows a typical Bolted Bonnet drawing. It is joined by studs and nuts with a gasket of suitable design/material placed between the flange surfaces to ensure sealing. The studs/nuts/bolts are tightened to the prescribed torques in a pattern defined by the manufacturer to ensure optimum sealing. However, as the system pressure increases, the possibility of leakage between the Body/Cover connection increases.

Let us now look at Figure 2 i.e. the Pressure Seal design given in detail. Figure 2 Note the differences in the respective Body/Cover connection configurations. Most Pressure Seal designs have “Cap tension bolts” to pull the Cap up and seal against the Sealing gasket seal. This creates a seal between the gasket and the inside diameter of the valve body.

The special feature of the Pressure Seal design is that as the system pressure increases, the pressure on the valve and the pressure on the pressure seal increases accordingly.

Therefore, with Pressure Seal Valves, as the system pressure increases, the potential for leakage through the Body/Lid decreases.

This design approach therefore has distinct advantages over Bolted Bonnnet design valves in main steam, feedwater, turbine bypass and other power plant systems that require valves capable of handling the challenges inherent in high pressure and temperature applications.

TYPES

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

FEATURES

1. There are no body-cover flanges or bolts exposed to pressure.
2. Forged steel material for all parts subjected to pressure. Optimized design for thermal fatigue required for power plant where frequent start-ups and shutdowns are mandatory.
3. Flanged valves are forged or full penetration welded with flanges integrated into the valve body.
4. Lighter design compared to bolted lid.
5. High quality packaging for reliable sealing and low emission performance.
6. The sealing surface is machined to the tightest tolerances and lowest roughness, ensuring reliable sealing and long service life.
7. High CV values.
8. OS&Y).
9. Low operating torque design.
10. Two pieces of self-aligning packing.
11. Graphite-based pressure seal with metal anti-extrusion cap.