Trunnion Ball Valve Design Features:
Trunnion Ball Valve Design Features
Double block and bleed (DBB)
API 6D defines a double block and bleed valve as a “single valve with two seating surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of vending/bleeding the cavity between the seating surfaces.”
When the ball is in the closed position, each seat seals off the process medium independently at the same time between the up/down stream and body cavity; it allows bleeding of the trapped cavity pressure (DBB) through drain or vent valve. The double block and bleed function makes it possible to flush the valve under pressure and verify that the seats are sealing properly.
Self Cavity Relief (Self Relieving Seat)
Trunnion ball valves constrain the ball by bearings. It is only allowed to rotate, but the ball seats can move. It also traps the media in the cavity when the operator closes the valve. It isolates the pipeline and the body cavity in the open and closed position. Thus, the pressure caught in the body cavity might be different from that in the line. The pressure increases in the cavity when heated. It pushes the ball seat of the downstream side away from the ball by rising pressure against the spring load. When this happens, the pressure gets released.
Secondary Metal to Metal Seat Design
Standard seat design is primary soft seal, and secondary metal to metal seal. Seat insert is designed as pressed-in type which is easy for maintenance. Optional design with primary metal to metal seal and secondary soft seal seat design is also available upon request.
Fire Safe Design
The fire safe designe is according to API 607 or other international standard. The trunnion ball valves are to meet the leakage as per standard even it is after fire.
The trunion ball valves (for 4″ and bigger) are designed with trunnion block instead of bottom stem. In this design, the ball will not rotate and the stem will not under pressure during the operation even it is with high pressure, which will reduce the operating torque.