In my experience most low pressure applications request 2 piece floating ball valves and when not specified I've always sold the 2 piece floater. What instances would a 150# or 300# trunnion be the preferred design. Also what is the advantage of a 3 piece vs a 2 piece body? If I'm installing a true double block and bleed valve (one that does not have self relieving seats), I use trunnion regardless of the size. I also specify trunnion for ESD valves. For ESD valves I've also been specifying Trunnion valves, but on certain critical spec breaks (one I did was ANSI 150 into SDR13.5 HDPE rated at 53 psig) I pull the body bleed and replace it with a PSV set at the downstream MAWP. Never had one of the PSV's go off, but I get a really warm and fuzzy feeling from installing them.Seems like a good idea to provide an extra level of protection for the downstream system. In full liquid systems also a good idea to prevent overpressuring of the body cavity if the valve heats up (solar radiation).

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