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Difference between floating ball valve and trunnion ball valve

2021-01-25

A Ball valve is a quarter-turn rotary motion valve that uses a ball-shaped disk to stop or start the flow. It resembles a plug valve in many ways. When a port in the ball is in line, it allows flow whereas when you rotate the valve 90 degrees, solid part of the ball stop the flow.
There are a lot of structures for ball valve, here we talk about the difference between floating ball valve and trunnion Ball Valve.
 

Floating Ball Valve

In a floating ball valve, the ball is held in the position by the compression of the two elastomeric seats against the ball. The ball is free to float inside the valve body.  The structure see below:

Floating Ball Valve structure Floating Ball Valve
The stem is connected to a slot at the top of the ball which allows the ball to rotate a quarter turn (90 degrees).  The shaft allows for a certain amount of lateral movement of the ball that is generated from the upstream pressure acting on the ball.  This small lateral movement, in fact, produces a load on the ball that presses it against the downstream seat which improves leak tightness of valve. This type of ball valve design is capable of bi-directional shut-off. The floating ball valve is very difficult to operate when upstream pressure is high. You can see above image of a floating ball valve.
 

Trunnion Ball Valve

Trunnion ball valve is a solution to the problem of excessive torque required by a floating ball valve in high-pressure service. A short shaft like an extension which is known as a trunnion set in the body. You can see this in the image.  In this design steam and ball work as a single unit. The ball is supported by two floating or spring-loaded seats that remain in constant contact with the ball.

Trunnion Ball Valve structure Trunnion Ball Valve

Trunnion ball valve design required a lower operating torque. Hence, reduces the size of the actuator and overall costs of the trunnion ball valve. This cost difference becomes an important factor when the pressure class and ball valve size increases. 


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