Fixed ball valve is mainly used in high pressure large diameter ball valve. According to the installation of the valve seat ring is different from a sphere of fixed valve seat and the ball before the seal after the sealing of the seat two structures.

Sphere before the sealing of the valve seat sealing principle: and stem as a whole sphere can slide up and down freely rotating bearing or bearings, valve seat ring is installed in the activities of the sleeve, the sleeve used in the body 0 ring seal. Valve seat ring installed in the sleeve by a group of pre-compression in the spring. Inlet valve seat, the valve is closed, by acting on the inlet diameter d and with the sleeve and the gate valve diameter D. Limited by the circumference of the ring to medium pressure on the surface pressure to the ball seat, and thus play the role of imports of seal, can not afford the export side of the seat seal. Reverse pressure, the seat will change in the role.

Body floating ball valve has two valve seat ring, clamping between them a sphere, sphere with holes, hole diameter equal to pipe diameter, called the entire diameter of ball; slightly smaller diameter hole the pipe diameter, said reduced diameter ball valve. With ball valve stem is free to rotate in the valve seat ring. In turn, the ball hole aligned with the pipe diameter, pipe work to ensure that the media of least resistance. When the stem turning 1 / 4 turn, the ball valve hole perpendicular to the channel, by adding to the two preload valve seat ring and media pressure to ball firmly pressed on the export side of the seat ring, thus ensuring valve is completely sealed. This valve is a single mandatory seal.

Floating ball valve seat materials should also consider whether the emphasis on ball withstand the load, because the ball things, except their own weight to bear all the load and the working medium to pass seat. In addition, consider the large diameter of the float valve in operation requires a larger force.

Floating ball valve in order to ensure tightness and reliability when working in contact with the ball and valve seat surface, the seal should be sufficiently high pressure ratio, but shall not exceed the allowable brass ball valve seat material than the pressure. With the groove in the seat should be close, or even a good seat on the tightness of the sphere, the media will end along the groove leakage. Sphere should have the correct geometry and low surface roughness. Usually h6 or h7 precision manufacturing sphere, the surface roughness is not greater than R.0.4, to improve the surface hardness and wear resistance of the sphere, the sphere surface should be hardened. Sealed plastic seat available, and should ensure close fit, shall not damage the sealing surface of the sphere. Meanwhile, the material should have sufficient strength to withstand higher than the pressure seal. PTFE is to create one of the most common seat material.

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