Fixed ball valves are mainly used in high pressure and large diameter ball valves. According to the installation of the seat ring, there are two kinds of structures: a ball seat sealed front and a valve seat sealed behind the ball.
Sealing principle of the valve seat sealed in front of the ball: The ball body integrated with the valve stem can be freely rotated in the upper and lower sliding bearing or the rolling bearing, the valve seat sealing ring is installed in the movable sleeve, and the sleeve is used in the valve body. The ring is sealed. The seat seal is pre-compressed by a set of springs mounted in the sleeve. The valve seat at the inlet end, when the ball valve is closed, depends on the diameter d of the inlet end and the diameter D of the sleeve that cooperates with the valve body. The medium pressure on the annular surface defined by the circumference presses the valve seat against the ball, thereby functioning as an inlet seal, and the valve seat at the outlet end does not seal. When pressed back, the function of the valve seat will change.
The valve body of the floating ball valve has two valve seat seals, and a ball is clamped between them. The ball has a through hole. The diameter of the through hole is equal to the inner diameter of the pipe, which is called a full diameter ball valve; the diameter of the through hole is slightly smaller than the pipe ball valve. . The ball can be freely rotated in the seat seal by means of the valve stem. When opened, the ball hole is aligned with the pipe aperture to ensure minimum pipe work medium resistance. When the valve stem rotates 1/4 turn, the ball hole is perpendicular to the passage of the valve, and the ball is tightly pressed against the valve seat seal ring at the outlet end by the pre-tightening force and the medium pressure applied to the two valve seat sealing rings, thereby ensuring the valve Completely sealed. It is a one-sided forced seal.
Floating ball valves should also focus on whether the seat material can withstand the load of the ball, because the ball, in addition to its own weight, also bears the full load of the working medium and transmits it to the valve seat. In addition, it is also considered that a large-diameter float valve requires a large force during operation.
In order to ensure the sealing and reliability of the floating ball valve during operation, the sealing surface of the ball and the valve seat should have a sufficiently high sealing specific pressure, but must not exceed the allowable specific pressure of the valve seat material. The fit of the valve seat in the groove should be tight, otherwise the medium will leak along the end face of the groove even if the valve seat is well sealed to the ball. The sphere should have the correct geometry and low surface roughness values. Generally, the sphere is manufactured with h6 or h7 precision, and the surface roughness value is not more than R.0.4. In order to improve the surface hardness and wear resistance of the sphere, the surface of the sphere should be hardened. The sealing seat can be made of plastic and should be tightly fitted so as not to damage the sealing surface of the ball. At the same time, the material should be strong enough to withstand high seal specific pressures. Teflon is one of the most commonly used materials for making seat seats.
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