A trunnion ball valve has mechanical anchoring of the ball at the top and the bottom, suitablf ro larger and higher pressure services. To ensure tight sealing at low pressure, high tensile springs force the seats against the ball while at higher pressure, the medium pressure pushes the upstream seat towards the ball.
For trunnion mounted ball valv size NPS 6 (ND 150) and above, it comes with provisions for sealant injection on both the stem and seat while for sizes NPS 5 (DN 125) and below on body cavity. In case of failed underperformed seals, a temporary emergency seal can be achieved by injecting sealants.
SINGLE PISTON EFFECT
DOUBLE PISTON EFFECT
Because the ball and stem in a ball valve are suspended on non-metalic parts, i.e. the seat seal and stem seal, there is a posibility a static charge may build up on the stem-ball, a mechanical (antistatic meal spring and ball) is introduced in the design to maintain the metal-to-metal contact between the rotating ball/stem and the valve body which will gournd any charges to the valve body.
FIRE SAFE DESIGN
During a fire, non-metallic soft material will be burnt, subsequently seal leakage or external leakage may occur and cause the fire spread or contaminate the environment. FBV ball valves are fire tested in accordance with API 6FA or API 607, witnessed and certified by TUV SUD. If a valve is not covered according to the standards, they are designed to be fire safe.