i have customer asking me about steam isolation ball valve .i am quoating 2'',3'',4'' #150 rating trunion ball valve for 450kpa.Most marketing departments get involved to come up with catchy names for RTFE, like Polyfill, TCM, or MN7, among others. Virgin TFE will extrude, and that little spurt of flashing as you open the valve with a puddle of condensate in the inlet won't do it any good. I respect gerhardl too much to disagree, but 450kPa is not much pressure, the valves are not large, and the saturation temp is less than 150C, so floating ball valves will serve well in this service for a much lower price than trunnion valves. Floating ball OR Truunion, blow down the lines scrupulously before installing new velves. It only takes a speck of weld slag to imbed in the seat and start a scratch on the ball to make a leaker. Good installation practice: Mount the valve close to the downleg for a steam trap. Mount the valve in a horizontal pipe with the valve-stem horizontal and the upstream side of the ball rising as it opens. (STEM ON LEFT IF LOOKING DOWNSTREAM). Avoid installing valves in vertical downward piping. These considerations keep sediment from collecting on the seats or in the cavity (or trunnion) and add greatly to the service life of the valve.

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