Automatic Body Cavity Relief In Ball Valves
cavity pressure relief is provided to relieve the trapped fluid into the internal pipeline, when the Ball Valve is closed with the fluid trapped in the body cavity and the pressure of the trapped fluid goes up abnormally as the unstable factor. Automatic cavity pressure relief is also called self-relieving seat in a ball valve.
When the valve is closed, the fluid is trapped in the body cavity of a ball valve. As an unstable factor, such as the rise in temperature, the trapped pressure will rise abnormally. It is harmful to the pipeline and may lead to serious risks.
As specified by API 6D, the body cavity pressure shall not exceed 1.33 times the valve pressure rating at the specified maximum operating temperature.
Cavity Relief in Trunnion Ball Valves
A trunnion mounted ball valves with single piston effect seats (SPE) design has an automatic pressure release into the pipeline. It uses “self-relieving seats” to release this pressure.
The trunnion-mounted ball valve also traps the media in the body cavity when the operator closes the valve. The pressure in the body cavity increases when heated and pushes the downstream ball valve seat away from the ball by rising pressure against the spring load. When this happens, the pressure gets released.
Cavity Relief in Floating Ball Valves
There are two ways of making cavity relief for floating ball valves.
1. Make a hole through the body cavity to access the valve port (bypass), so the body cavity and the port are at the same pressure condition when the valve is fully closed.
2. In the case of increased temperature, valve position is “full open” and fluid pressurizing direction “1-way”.
1). Make a relief groove on the upstream side of the ball seat.
2). Cut a hole in the ball face on the upstream side of the port pass.
EQUALIZED CAVITY PRESSURE
The pressure equalization hole at the top of the ball combined with the seat design are both engineered to maintain the pressure balance in the line and in the body cavity while the valve is in open position
PROINAD92,S.L.
