Most low pressure applications request 2 piece floating ball valves and when not specified we've always sold the 2 piece floater. Whatinstances would a 150# or 300# trunnion be the preferred design. Also what is the advantage of a 3 piece vs a 2 piece body?There are a variety of rules of thumb for when to switch from floating to trunnion mounted. Ourselves, We specify trunnion mounted at 12" in Class 150 and 8" in Class 300. However, there is no hard and fast reference and different people have different Ball Valves Resilient Seated Gate Valvessizes and pressure classes are one or the other. For really low pressure operations (i.e., from deep vacuum to about 10 psig) inBellows Seal Valves gas I specify trunnion down to 4-inch because I've had problems with floaters being able to shift ball enough to seal at very low dP after Resilient Seated Gate Valvesthey've been in service a couple of years. For normal pressures I look at the service to decide if I want trunnion or floater at 6-inch ANSI 300--if company policies allow me to use a trunnion for double block and Butterfly Valvesbleed I use trunnions for 6-inch, if not I use floaters. For 8-inch and above (ANSI 300) I use forged Gate, Globe, Check Valvestrunnion like rneil. I don't do much in ANSI 150 so I haven't thought about that one enough.

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