Le 27 août 2016, 18:35 dans Humeurs • 0
Trunnion Ball Valve
Trunnion Ball Valves General Design
The ball is fixed by trunnion or trunnion support, and the seat rings are floating, free to move against the ball along the valve centerline. The trunnion/trunnion support together with bears adsorb the side load created by the pressure acting on the ball. At low pressure, the seat tight sealing is ensured by the preload of the springs acting on the seat rings. Along with the pressure increasing, the process medium pressure pushes the seat rings agains the ball to provide additional load for tight sealing.
The ball and stem are independent with each other to minimize the effect of the side thrust genrated by the pressure actiing on the ball.
Ball Seat Alignment
Mechanical stops are equiped on all valves to ensure the ball is never to be over rotated.
When valves are used under high pressure gas applications, e.g. hydrocarbon gas service under class 600 and above, the gas may be absorbed into the molecular structure of elastomeric O-rings. If the valve is subjected to sudden decompression, the O-rings may be destroed by the rapidly expanded gas. To avoid this possiblity, special AED O-rings or Lip seals, suitable for such service conditions. Are available on request.
Enviorenment Friendly Valve
Accurate maching of stem, gland and body sealing surfaces with double sealing (O-ring primary seal plus graphite gasket seal) ensure the low emission which is complying with the most servere pollution-control regulations. The test certificats are available on request.
Standard seat design is primary soft seal, and secondary metal to meal 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.
a) Standard: Single Piston Effection Seats ( Self Relieving Seats)
Medium pressure, both upstream and downstream, creates a resultandt trust to the seat rings against the ball to assure the tight sealing; Medium pressure action in the body cavity creates a resultant thrust to push the seat rings away from the ball.
The single piston design permits the automatic release of any over pressure in the body cavity when the valve is fully open or fully closed position.
b) Option 1: Double Piston Effect Seats
Medium pressure, both upstream and downstream as well as in the body cavity, creates a resultant thrust that pushes the seat rings against the ball. Valves with double piston effect seat
rings require a cavity pressure relief device to reduce the build-up of over pressure in the body cavity.
c) Option 2: Combination Seats
Combination seats design is available on request. That is a stanadard seat design used for upstream side and a double piston effect seats design used for downstream. The advantage is it can reach double piston effect seats design function without cavity pressure relief device to save the cost, meanwhile only need a little care to install valve per flow direction arrow.
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.(Fig. 7)
Trunnion Mounted ball valves Blow-out Proof Stem
The stem is made separately from the ball with integral T-type round shoulder, retained by gland. (other designs are available on request).(Fig. 8)
Spring plus graphite type antis tatic device are applied between the ball, stem, gland flange and body, to keep the electrical continuity between all the metallic components, and ensure the resistance lower than the most severe service requirement.(Fig. 8)
a) External leakage prevention All the possible external leakage point between stem and gland flange, gland flange and body, body and adapter are sealed with primary O-ring then secondary graphite gasket. When fire burned out the primary O-ring seal, the secondary graphite gasket seal still can prevent the process medium from external leakage.(Fig. 9)
b) Internal leakage prevention When fire burned out the primary O-ring seal between the floating seat ring and adapter, also the seat insert between seat ring and ball, the secondary graphite seal between seat ring and adapter, and seat ring & ball metal to metal contact preloaded by spring will minimize the internal process medium leakage. (Fig. 10, 11)
Emergency Sealant Injection System
Each valve of size 6” and larger (or smaller size on request), is equipped with sealant injection located at stem and seats area. The injection is integrated with check valve to provide backup sealing, also a check valve is equipped at front of seat sealant injection to avoid blowing out in case wrong operation. When the soft sealing materials (seat inserts and o-rings) are damaged and leakage happened by fire or other accident, the sealant can be injected through the injection fittings.(Fig. 12)
This is from:Trunnion Ball Valve