Sealing principle of fixed ball valve and floating ball valve

Fixed ball valves are mainly used in high-pressure and large-diameter ball valves. According to the different installation of the valve seat sealing ring, the fixed ball valve has two structures: the valve seat sealed in the front of the ball and the valve seat sealed behind the ball. The sealing principle of the valve seat sealed in front of the ball: the ball that is integrated with the valve stem can rotate freely in the upper and lower sliding bearings or rolling bearings. The valve seat sealing ring is installed in the movable sleeve, and the sleeve is used in the valve body. 0 Ring seal. The seat seal is pre-compressed by a set of springs mounted in the sleeve. The valve seat at the inlet end acts on the diameter d of the inlet end and the diameter D of the sleeve matched with the valve body when the ball valve is closed. The medium pressure on the annular surface defined by the circumference of the valve seat presses the valve seat against the sphere, so as to play the role of sealing at the inlet, and the valve seat at the outlet end does not have a sealing effect. When reverse pressure is applied, the action of the valve seat will change. There are two valve seat sealing rings in the valve body of the floating ball valve, and a ball is clamped between them. There is a through hole on the ball. The diameter of the through hole is equal to the inner diameter of the pipeline, which is called a full diameter ball valve; the diameter of the through hole is slightly smaller than the The inner diameter is called a reduced diameter ball valve. With the help of the valve stem, the ball can rotate freely in the valve seat seal. When opening, the ball hole is aligned with the pipe diameter to ensure the minimum resistance of the pipe working medium. When the valve stem rotates 1/4 turn, the ball hole is perpendicular to the channel of the valve, and the ball is tightly pressed on the valve seat sealing ring at the outlet end by the pre-tightening force and medium pressure applied to the two valve seat sealing rings, so as to ensure the valve Completely sealed. This ball valve is a single-sided forced seal. The floating ball valve should also focus on whether the seat material can withstand the load of the ball, because the ball bears the full load of the working medium in addition to its own weight 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 performance and reliability of the floating ball valve during operation, there should be a sufficiently high sealing specific pressure on the contact surface between the ball and the valve seat, but it should not exceed the allowable specific pressure of the valve seat material. The fit of the valve seat in the groove should be tight, otherwise even if the valve seat seals against the ball well, the medium will leak along the end face of the groove. The sphere should have the correct geometry and a low surface roughness value. Usually, the sphere is manufactured according to h6 or h7 precision, and its surface roughness value is not greater 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 valve seat can be made of plastic, and should ensure a tight fit without damaging the sealing surface of the sphere. At the same time, the material should have sufficient strength to withstand high sealing specific pressure. PTFE is one of the most commonly used materials for valve seats.
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