Large-diameter ball valve of the Classification and Technical Specifications

Ball valve, the valve is applied more widely, one of which appears very early, promote the use of late. It works the same as with the plug valves are rotated by the valve spool to make the hoist, but the light switch than the plug valves, relatively small size, can be made into large-diameter valves. Valve sealing reliability, simple structure, easy maintenance, sealing surface and the ball often in the closed state, can not easily be medium erosion. At present, foreign valve diameter has reached 3050cm, in petroleum, chemical industry, metallurgy, textile, food, atomic energy, aviation and other departments widely used.

1, ball valve classification



Valve is divided into two main categories: floating, fixed (see Figure 1)











a, floating ball valve















b, fixed ball valve



Figure 1 floating, fixed ball valve structure



1.1, floating ball valve



The sphere is a floating ball valve in the medium under pressure to produce a certain degree of displacement of the sphere, and pressed in the export side of the sealing surface to ensure the valve seal. Floating ball valve of simple structure, good sealing, but the ball to bear the load all the working medium to pass the export ring, so to consider the ring material can withstand the work load of the sphere medium. This structure is widely used in the low-pressure valve.



1.2, fixed ball valve



The ball valve is fixed, the pressure does not produce after the move. Fixed ball valve comes with a floating valve seat, by the medium pressure, the seat produce movement, so that pressed the ball on the ring to ensure sealing. Usually with the sphere of the upper and lower shaft bearings, operating torque is small, applied to high pressure and large-diameter valve. In order to reduce torque and increase the operation of valve sealing reliability of the valve seal has emerged in recent years, both in injection pressure between the sealing surface of a special lubricant, to form a layer of film that enhances the tightness, but also reduce operating torque, more suitable for large-diameter high-pressure valve.



This paper mainly large-diameter floating ball valve open and close the tightness of torque, etc. as shallow, hoping to be helpful for the application of ball valves.



2, floating ball valve seals



Floating ball valve of simple structure, good sealing, but the ball to bear the load all the working medium to pass the exit seal, so ring material can withstand the work load of the medium sphere is the key. In general, seals are PTFE and other flexible materials used, the composition of metal and nonmetal materials, seal pair, which is often referred to as soft-sealing. Soft seal tightness easy to guarantee, but also to seal the surface of machining accuracy and surface roughness requirements are not very high. In the medium pressure, ball to the exit of displacement and compaction seat, this time, ball pressure in the valve seat on the edge QMJ as follows:



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