For Ball Valve, there are 2 types design "Floating type" & "Trunnion type".
- Float ball valve: the ball is held on two seat rings.
- Trunnion ball valve: the ball is supported on its vertical rotation axis by a trunnion. The trunnion absorbs the pressure from the flow, therefore the contact between the ball and the seat is not excessively stressed and the operating torque can remain low. This design is recommend for big diameters and high pressure.
The left-hand photograph shows the construction of float ball valve, Floating ball is that ball pinched by 2pcs of ball seats and sealed. Ball is not fixed position.
while the right-hand photograph shows the construction of trunnion ball valve, Trunnion Ball is fixed position by upper and lower stems, and sealed for ball seats pushed to the ball by spring and fluid's pressure.
Read more: http://knowledge.tue-center.com/category/shutdown-valves/