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One, floating ball valve, ball valve is floating, under the effect of medium pressure, the fitness ball produce certain displacement and compression at the outlet seal surface, guarantee the outlet seal.
Floating ball ball valve has simple structure, good sealing, but all spheres of work under medium load to export seal, therefore should consider to seal material can withstand sphere medium working load.In this structure, it is widely used in low pressure ball valve.
Second, the fixed ball ball valve ball valve ball is fixed, does not produce mobile after compression.
Fixed ball valves have a floating ball valve seat, the medium pressure, mobile seat, make the seal compression on the ball, to ensure the seal.
Usually mounted on the upper and lower shaft with ball bearing, the operating torque is small, suitable for high pressure and large diameter of the valve.To reduce the number of ball valve operating torque and increase the reliability of the sealing, appeared in recent years, oil seal ball valve, both betting special lubricant between the sealing surface, in order to form a layer of oil film, which increases the sealing, and reduce operating torque, suitable for high pressure large diameter ball valve.
Three, elastic ball ball valve ball valve is elastic sphere.
Ball and seat sealing adopts metal materials, sealing pressure is very big, relying on the pressure of the medium itself already could not reach the requirements of sealing, must exert external forces.
This valve is suitable for high temperature and high pressure medium.
Elastic ball is on the lower end of the sphere wall open one elastic slot, and elasticity.When close the channel, sphere rolling out with stem wedge-shaped head pressure to seal with the valve seat.
Wedge head before you turn the sphere are released, the sphere then restore the original prototype, appear very small gap between the sphere and valve seat, can reduce the sealing surface friction and operating torque. 
A, open the process
1 in the closed position, the sphere of stem [/ wiki] [wiki] machinery pressure function, press the seat.
2 when turn the handwheel counterclockwise, the valve stem is reverse movement, the Angle at the bottom of the plane to make the ball off the seat.
3 stem continue to ascend, and valve stem guide pin of interaction in the spiral groove, the sphere began to rotate without some friction.Until 4 to full open position, the valve stem to limit position, sphere rotation to the full open position.
B, the closing process
1 closing, rotating the handwheel clockwise, stem began to drop and the ball left seat begin to spin.
2 continue to rotate the handwheel, the valve stem is embedded in the spiral groove on the role of the guide pin, the stem and ball rotate 90 ° at the same time.
3 is close to closing, the sphere has been without contact with the valve seat rotated 90 °.
4 wheel rotation of the last few laps, stem mechanically wedge Angle at the bottom of the plane to the oppression of a sphere, make its strong pressure on the seat, to completely seal.