The seat design of trunnion ball valve includes the DBB, single piston effect, or double piston effect, as well as emergency injection fittings.

Trunnion Mounted Ball Valve Seat Design Features

Double Block and Bleed (DBB)

Single valve with two seating surfaces, that in the closed position, provides a seal against the pressure from both ends of the valve with a mean of venting/bleeding the cavity between the seating surfaces.

Single Piston Effect 

(SPE)/Self-Relieving Seats

Standard seat design is SPE seat or self relieving seat with a soft seat insert. Under normal working conditions, the resultant pressure force pushes the seat against the ball to ensure a tight seal.

DOUBLE PISTON Effect (DPE)/Double Isolation Block and Bleed

The DPE seat is an optional feature. The seat design comprises of a unique seal design that allows the seat to seal in both directions with the pressure either acting from the upstream or downstream of the seat. When the pressure is applied from the upstream, the DPE seat works just like the SPE seat design. When the pressure is acting from the downstream or body cavity, the floating seal design allows the downstream pressure to push the seat against the ball. Note that the DPE seat configuration does not have self-relieving capability, and it requires a pressure relief valve to be installed in order to avoid the pressure build up inside the body cavity.

Seat/Ball Sealing

To reduce the operating torque, the seat is designed with a pressure assisted sealing mechanism coupled with seat springs to ensure a tight seal under very low differential pressure conditions. The seat insert is made from a thermoplastic material and can be offered with a variety of materials for specific applications. Single Piston/ SPE is standard. Double Piston/DPE is optional.

Seat/Body Sealing 

Fire-safe seat design is a standard feature. The seat/body seal design includes a combination of soft seal and graphite seal.

Emergency Seat Sealant


Under normal operating conditions, Relia

trunnion valves do not require sealants

or lubricants. In the unlikely event that

the seat gets damaged, an emergency

shutoff may be achieved with a sealant

injected into the seat sealing area.


  • Requires a check valve
  • Not available on smaller sizes

(3″-4″ CL 150/300)


Emergency Stem Sealing & Sealant Injection

Standard stem seal configuration consists of double O-Rings and a graphite seal ring. In the unlikely event that the soft seals get damaged, the seal can be restored by injecting valve sealant into the sealing area through the sealant fitting.

Fire-safe Metal Sealing

After Fire

Anti-Static Device

If the soft seat insert gets damaged due to fire, the seat is designed with a secondary sealing mechanism

that allows a metal-to-metal contact between the seat and ball. This secondary metal sealing is a standard

feature for all Relia soft-seated trunnion mounted ball valves.


Anti-static devices between

  • Body and Stem
  • Stem and Ball

© 2019 Zhejiang Relia Valve Co., Ltd.,China