Valve knowledge: ball valve

- Dec 19, 2017 -

The ball valve and the plug valve belong to one type of valves. Only its closing member is a sphere. The ball is rotated around the center line of the valve to achieve a valve open and close. The ball valve is used in the pipeline to cut, distribute and change the flow direction of the medium. Ball valves are widely used in recent years, a new type of valves, ball valves and plug valves belong to one type of valves. Only its closing member is a sphere, and the sphere is rotated around the center line of the valve to achieve a valve opening and closing.


The ball valve is used in the pipeline to cut, distribute and change the flow direction of the medium. Ball valve is a new type of valve which has been widely used in recent years. It has the following advantages:


1. the fluid resistance is small, and the resistance coefficient is equal to the tube length of the same length.


The 2. is simple in structure, small in size and light in weight.


3. closely dependable, the sealing surface materials of the ball valve are widely used in plastic and sealed, and are also widely used in the vacuum system.


4. easy operation, open and close rapidly, from fully open to fully closed as long as 90 degree rotation, facilitate remote control.


5. convenient maintenance, the ball valve structure is simple, sealing ring is generally active, disassembly and replacement is more convenient.


6. the sealing surface of the ball and the seat is isolated from the medium when it is fully open or completely closed. When the medium is passed, it will not cause the erosion of the sealing surface of the valve.


7. a wide range of applications, path from a small to a few millimeters, a few meters large, from high vacuum to high pressure can be applied.


Ball valve has been widely used in oil, chemical, power generation, paper, atomic energy, aviation, rocket and other departments, as well as people's daily life.


The ball valve can be divided according to the structure form:


One, floating ball ball valve

The sphere of the ball valve is floating. Under the action of medium pressure, the sphere can produce a certain displacement and tightly press on the sealing surface at the outlet side, so as to ensure that the outlet ends are sealed.


The floating ball valve has the advantages of simple structure and good sealing, but the load that the ball bears the working medium is all passed to the export sealing ring. Therefore, we need to consider whether the material of the sealing ring can withstand the working load of the ball medium. This structure is widely used in medium and low pressure ball valves.


Two, fixed ball valve

The sphere of the ball valve is fixed and does not move after being pressed. The ball valve with a fixed ball has a floating seat. The valve seat is moved by the pressure of the medium, so that the seal is pressed on the ball to ensure the seal. Usually with the ball in the upper and lower shaft with bearings, operating torque, suitable for high pressure and large diameter of the valve.


In order to reduce the valve operating torque and increase the reliability of the seal, valve seal has emerged in recent years, both the pressure injection of a special lubricant in the sealing surface, to form a layer of film that enhances the sealing, and reduce operating torque, more suitable for large-diameter high-pressure valve.


Three, elastic ball ball valve

The ball of the ball is elastic. The ball and seat gasket are made of metal materials. The sealing ratio is very high. The pressure of the medium itself has failed to meet the requirements of sealing, and external force must be applied. This valve is suitable for high temperature and high pressure medium.


The elastic sphere is an elastic groove at the lower end of the inner wall of the sphere, and the elasticity is obtained. When the channel is closed, the wedge head of the stem is used to make the sphere open and the seat press tight to seal. Before rotating the ball, the wedge head is loosened first, then the sphere is restored to the original shape, so that there is a small gap between the ball and the valve seat, which can reduce the friction and operation torque of the sealing surface.


The ball valve can be divided into straight through, three general and right angle type according to its channel position. The latter two kinds of ball valves are used to distribute the medium and change the flow of the medium.


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