DAFRAM trunnion mounted ball valves are built as standard in accordance with the design requirements of API 6D or API 6A, both in two and three piece bolted construction.
Independent floating spring loaded seat rings are always in contact with the ball to provide an effective tight seal at low differential pressures.
At higher differential pressures, the upstream seat ring becomes pressure energised against the ball to ensure the seal, whilst the downstream seat remains spring loaded.
The whole range may be supplied with two basic seating design criteria:
- SELF RELIEVING SEATS (standard) providing the self relieving of the body cavity overpressure
- DOUBLE PISTON EFFECT (upon request) providing a double barrier against the fluid. In this case when the upstream seat fails, the downstream seat ensures the seat tightness (the valve body is equipped with an automatic safety valve to release the body overpressures in case of expanding fluids).