Ball valve and plug valve are of the same type of valve, and only its closure is a sphere, the sphere around the centerline of the valve body to rotate to achieve open, close a valve. Ball valve is mainly used in the pipeline to cut off, distribute and change the flow direction of the medium. Ball valve is widely used in recent years, a new type of valve, which has the following advantages: 1. Fluid resistance is small, the resistance coefficient and the same length of the pipe section. 2. Simple structure, small size, light weight. 3. Tight and reliable, the current ball valve sealing surface material widely used plastic, good sealing, vacuum system has also been widely used. 4. Easy to operate, quick opening and closing, as long as 90 ° rotation from full open to full close, easy to remote control. 5. Easy maintenance, ball valve structure is simple, the seals are generally active, demolition and replacement are more convenient. 6. In the fully open or fully closed, the ball and valve seat sealing surface and media isolation, the media will not cause erosion of the valve sealing surface. 7. Wide range of applications, the path from small to a few millimeters, up to a few meters, from high vacuum to high pressure can be applied. Ball valve has been widely used in petroleum, chemical, power generation, papermaking, atomic energy, aviation, rockets and other departments, as well as people's daily lives. Ball valve structure can be divided according to the structure: First, the floating ball valve ball is floating, under the media pressure, the ball can produce a certain displacement and squeeze the sealing surface of the outlet end to ensure that the outlet seal. Floating ball valve structure is simple, good sealing, but the ball to withstand the load of the working medium all to the export seal, so to consider whether the seal material can withstand the working load of the ball medium. This structure is widely used in low pressure ball valve. Second, the fixed ball valve ball valve ball is fixed, does not produce pressure after the move. Fixed ball valve with a floating valve seat, subject to media pressure, the valve seat to move so that the ring is pressed on the ball in order to ensure the seal. Usually with the ball on the lower shaft equipped with bearings, operating torque is small, suitable for high pressure and large diameter of the valve. In order to reduce the operating torque of the ball valve and increase the reliability of the seal, in recent years there have been oil seal ball valves, both in the sealing surface injection of special lubricants to form a layer of oil film, which enhanced the tightness and reduced operating torque , More suitable for high pressure large diameter ball valve. Third, the flexible ball valve ball is flexible. Sphere and seat ring are made of metal materials, sealing a large pressure, relying on the pressure of the media itself has reached the seal requirements, must impose external forces. This valve is suitable for high temperature and pressure medium. Elastic ball is in the lower end of the ball wall to open a flexible groove, and to obtain flexibility. When closing the channel, the wedge-shaped head of the valve stem causes the ball to expand and press against the valve seat to seal. Before turning the sphere, the wedged head is released and the sphere then restores its original shape. This results in a small gap between the sphere and the seat, which can reduce the friction and operating torque of the sealing surface. Ball valve can be divided according to their channel position through-type, three-way and right angle.
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