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How Does a Ball Valve Work?

The author:admin Release time:2020-09-24 browse:
Generally speaking, the ball valve working mechanism works this way. Whether it is manually or actuator operated, some force moves the lever or handle to a quarter turn to open the valve. This force is transferred to the stem, moving the disc to open.

The ball disc turns and its hollowed side faces the flow of media. At this point, the lever is in the perpendicular position and the port to parallel in relation to the flow of media. There is a handle stop near the connection between the stem and bonnet to only allow a quarter-turn.

To close the valve, the lever moves back a quarter turn. The stem moves to turn the ball disc in the opposite direction, blocking the flow of media. The lever is in the parallel position and the port, perpendicular.

However, take note that there are three kinds of ball disc movement. Each of these has different working operations.

The floating ball valve has its ball disc suspended on the stem. There is no support at the bottom part of the ball so the ball disc partially relies on the internal pressure for the tight seal ball valves are known for.

As the valve closes, the upstream linear pressure from the media pushes the ball towards the cupped downstream seat. This provides a positive valve tightness, adding to its sealing factor. The downstream seat of the floating ball valve design carries the load of the internal pressure when the valve is closed.

The other kind of ball disc design is the trunnion mounted ball valve. This has a set of trunnions at the bottom of the ball disc, making the ball disc stationary. These trunnions also absorb the force from the pressure load when the valve closes so there is less friction between the ball disc and the seat. Sealing pressure is performed in both upstream and downstream ports.

When the valve closes, spring-loaded seats move against the ball which only rotates in its own axis. These springs push the seat tightly to the ball. Trunnion mounted ball types are suitable for applications that don’t need high pressure to move the ball to the downstream seat.

Lastly, the rising stem ball valve utilizes the tilt-and-turn mechanism. The ball disc wedges to the seat when the valve closes. When it opens, the disc tilts to remove itself from the seat and allow media flow.
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