Wegman valves offers various types of ball valves
A trunnion mounted ball valve has the ball fixed on trunnions and the seats press against the ball .
The seats have springs that press them against the ball, the medium assists the springs to seal off on the ball.
Standard the seats are pressure relieving (SPE), this means the pressure that can build up in the body finds its way past the seat(s). In principal the pressure can go both ways, up and down stream.
In special circumstances one or both seats can have the double piston effect (DPE), simply stated that type of seat does not allow the seat to move from the ball due to (over)pressure from an unwanted side. Special care is required with regards to safety and installation.
A trunnion mounted ball valve body can be made of forged or cast material.
The body can consist of 2 or 3 pieces which can be called: end entry, 2 piece body, split body, 3 piece body.
Typically available from 2” till very big where the cast version is more limited in size and pressure rating.
The available port or bore size is reduced or full. Reduced is normally 1 pipe size smaller (sometimes more) and full is, the same as the pipe size. Check the standards for the actual dimensions.
Body materials can be almost any, the most common are: forged or cast steel (A216 WCB / WCC, A105, LF2) and Stainless Steel (CF8M, F316). Where lined valves are common with the floating design, in trunnion the valve is high alloy or cladded (strong base material with corrosion resistant layer welded on it)
Seat materials typically are: Nylon, Devlon, Teflon (TFE, PTFE, CTFE, etc.), metal (hardened), PEEK, KEL-F (PCTFE).
If you want to use a ball valve to “control” the flow it can have a cage or drilled pattern in the ball.
The body parts are typically bolted together but fully welded is possible.