What is an Eccentric Semiball Valve?
An eccentric semi-ball valve is similar in principle to a conventional ball valve, but with a half ball that makes a “C” shape. This C-shaped ball rotates on two planes of motion with energy from the stem to close and seal against a fixed seat.
The eccentric semi-ball valve and flange valve belong to the same type but the difference is that the closure member of the eccentric semi-ball valve is a sphere and this sphere can rotate around the center line of the body to achieve the open and close movement. Ball valves are mainly used for cutting, distributing, and changing the direction of the media flow in pipeline applications. Two-piece ball valves and three-piece ball valves are new kinds of valves that have been widely used in recent years.
Structure of Semiball Valve
An eccentric semi-ball valve is composed of a body, eccentric shaft, bonnet, spherical cap, axle sleeve, seat, and other components. With 90-degree rotation by eccentric shaft, the valve can achieve open and close movements and plays a role in cutting off the media. An eccentric half-ball valve can avoid the friction between the seat and spherical cap and because of the adoption of the eccentric crank, there is an eccentricity between the center line of the spherical cap and valve runner. When the valve is open, the crank turns at a slight angle. At this moment, the spherical cap will leave the seat and have no more connection; on the contrary, in the close process, only at the close moment can the spherical cap contact the seat.
Specifications of Eccentric Semiball Valve
- Design and Manufacture: API6D/GB/T 12237
- Face to face: API 608, API 598, API607/GB/T12221
- Flange connection: ANSI B16.5/ JBT/79
- Temperature: not beyond 160oC
- Nominal pressure: 0.6-16MPa
- Size: 1″-40″
- Medium: liquid, oil, serous, particles of slag, air
- Material: WCB
- metal sealing semi-ball valve, electric actuator ball valve, float valve, actuator ball valve
Structural Features of Semiball Valve
- The hemisphere of the double-eccentricity half-ball valve adopts the double eccentric design, it has reliable sealing, instantaneous release, small torque, and long service life, and it can be used in the harsh working condition of transporting granule medium. The structure principle is that the hemisphere center line has set oversize with the stem center line and the seat center line. When fully open, the sphere and the valve seat separate completely, and there is a certain space. The radius of gyration is divided into a long radius and a short radius. There will be a θ angle between the tangent line on the long radius turn trajectory and the seat sealing surface. When the valve opens and closes, the relative seat surface of the hemisphere will have a coming-out separation and a coming-in extrusion, thus reducing the mechanical wear and abrasion between the seat and the hemisphere during operation, improving the service life.
- Valve seat
- the seat is designed floating, which reduces the processing difficulty, ensuring the coincidence between the center line of the valve seat and the spherical centering point of the hemisphere, thus improving the sealing performance. There is space between the seat and the body, so when installed it can automatically find the mid-line by hemisphere locating, to ensure full contact between the seat sealing surface and the spherical surface, this solves the leakage due to the machining accuracy of error, improving the use of ball valve performance and its service life.
- The seal of the seat and the body is a hard-to-seal structure, suitable for high temperature and high-pressure conditions. The seat and the sealing contact surface have a small c-value, and each seal surface has a high accuracy requirement. When installed, a retainer is equipped with an electric impact wrench. It is not only the retainer meshing with the valve body to prevent the loss, but also the seat rubbing and rotating. It conforms to the principle of mechanical vibration meshing, making the seat and the body sealed with reliability.
- It is two hard seals between the seat and the body or the seat and hemisphere, so this valve can be used in high temperature and high-pressure conditions.
- Other mechanical components
- The whole valve adopts a modular design, simple structure, good reliability, and high generality. The valve stem adopts the jet structure. Diversified driving mode. The connection dimension of the valve stem, bracket, and actuators conform to ISO5211 standards, it can be directly assembled with various specifications actuators. The commonly used driving modes are manual, pneumatic, hydraulic and electric, gas and liquid linkage, etc, improving the performance of the double eccentric half-ball valve.
Applications of Semiball Valve
This series of valves are applicable in fields of petroleum, chemical industry, metallurgy, steel, electric power, light power, light spinning, paper making, sewage treatment, etc., and also applicable for low-pressure pipes. It can transport all kinds of eroded particles and gas medium under temperature and middle temperature, stop current, and adjust the flux, without medium effect.
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