How Does The Pressure Seal Work?
Pressure sealing is a valve design concept that offers distinct advantages over traditional bolted body-to-bonnet sealing mechanisms. It utilizes valve system pressure to provide sufficient force to the internal diameter (ID) of the valve body and the bonnet surface. As system pressure increases, the force on the pressure seal gasket increases.
Although the only working part of the gasket is the apex or toe, the pressure seal conforms to the ID of the valve. When the system pressure is activated, the toe forms a seal that can hold thousands of pounds of pressure and keep the system media inside the valve.
For the most part, it is used for high pressures in power generation, pulp and paper, refineries, and even chemical plants. Because of the dependence on system pressure to maintain a seal, these valves are best suited for systems with minimum working pressures in excess of 500 psi.
CDType Sealing Components
Are pressure seals new?
The design of pressure seal valves dates back as far as the 1900’s. Its use increased significantly in the late 1940’s to early 1950’s as warfare technology began to be used in consumer applications. Further pressure seals were developed to reduce the weight of larger ships. At that time, all ships were propelled by steam engines, and the reduced weight improved the maneuverability and mobility of the ships.
Since steam generation required many valves, reducing the weight of these valves significantly reduced the overall weight. In high-pressure systems, shut-off valves, control valves and many boilers with drain and shock valves operate. It also includes the piping that holds it together. If the weight of each valve is reduced by 100 pounds, multiplied by one thousand valves, a significant amount of weight is eliminated.
Pressure sealing is a valve design that offers distinct advantages over the traditional bolted body-to-bonnet sealing mechanism. It uses valve system pressure to keep the thousands of pounds of pressure and system media contained within the valve.
D Type Sealing Components
Prior to the development of pressure seal valves, all valves used bolted bonnets to keep pressurized media inside the valve. The bonnets were very heavy. Their removal was seen as a way to relieve a significant amount of weight. The new design uses a metal pressure seal that eliminates the need for a bolted bonnet. This is very effective, saves a lot of weight and changes the valve design forever.
How does the pressure seal work?
The pressure seal gasket must conform to the bore of the valve body and the clearance between the seals, and the valve body must be small. Pressure seal gaskets are typically made of malleable cast iron and then treated with silver to help maintain consistency. The construction of the seal consists of a wider top, an angle consisting of 45 or 30 degrees, and a wire-thin toe at the bottom.
The pressure seal gasket is placed directly below the positioning ring. With enough force, the metal will move into the correct position and press the toe between the body ID and the hood surface. When the system pressure opens, the seal becomes a permanent part of the valve until it needs to be replaced.
The pressure on the gasket in pounds per square inch is tremendous. It can be calculated by multiplying the system pressure by the area of the valve cover, which is equal to the amount of force generated by the system. For example, for 2,000 pounds per square inch multiplied by 10 inches of pipe, the load is 157,000 pounds. Considering that the Space Shuttle weighs 292,000 pounds, the weight required to launch it is not much in terms of load.
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