Double Piston Ball Valve, API 6D
Key Specifications / Features
Double Piston Ball Valve provides a contemporary seal at both the upstream and downstream sides. This system does not enable the automatic self-relieving of the excessive pressure in the body cavity., therefore it is necessary to use an external safety relief valve. Such a device can be avoided if at least one of the seats is of single piston effect type, but in such case the valve is unidirectional.
Double piston effect seats are pressure energized in both direction. They will not release valve body cavity overpressure, a pressure relief design shall be added then.
However, double piston effect seats offer valve sealing redundancy.
If upstream seat fails, downstream seat can still insure valve tightness. Interesting in specific applications (high integrity required) or for some pipe testing issues during construction.