Turnnion Ball valve

Turnnion Ball valve

The ball valves generally fall into one of two categories, a floating ball valve or a trunnion type ball valve. A trunnion ball valve is often preferred as it has a distinctive lower operating torque than the floating ball valve since pressure forces tending to push the ball downstream are supported by a trunnion rather than the valve seat.

Trunnion ball valve is fixed, so that it does not move within medium pressure. Trunnion ball valve usually has floating seats.  The seats move within the medium pressure to tight the ball and seal ring to ensure sealing reliability. Bearings could be mounted in top shaft and bottom shaft, which reduces operation torque. This is widely used in valves that can endure high pressure. To decrease the operation torque and increase sealing reliability, lubricated ball valves are adopted in recent years.

In certain applications, the trunnion valve has an additional advantage in the fact that when the ball valve is in the closed position the upstream seal is under line pressure while the downstream seal is pressure relieving, eliminating the possibility of a pressure lock in the center cavity.