Leakage class of control valve
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I believe the leakage rating for control valves specified in ANSI/FCI 70-2 is six levels; is there a TSO level as well? Thank you all. Also, if you have this standard, could you share it? :lol
The control valve is marked with the abbreviation TSO, which stands for Tight-Shut Off – it closes tightly when shut. It indicates that the leakage level is determined according to the project specifications; it is generally grade V, with grade VI existing as well. The sealing class of ordinary control valves is grade IV, while the sealing class of isolation valves is grade V (hard seal) or grade VI (soft seal).
What I saw in the control valve data sheet was ANSI/FCI CLASS VI; it is intended for use as a regulating valve
TSO stands for tight shutdown, which means shutting it off a bit further than the normal fully closed position. It is not related to the leakage level, but generally a leakage level of Class V is required. As for Class VI proposed by LZ, FCI 70.2 states that this class is typically applied in the case of valve seats made of elastic materials. In other words, for ball valves with a Metal-to-Metal seal, if there are no elastic elements behind the retainer, grinding alone is not sufficient to achieve Class VI performance; therefore, for ball valves operating under the stringent conditions of TSO, the Class VI option is not available.
As a leakage rating, TSO has nothing to do with ANSI FCI; it’s just that domestic petrochemical standards combine the two. The testing standards for these two are different – the testing pressure for TSO is higher, around 3.5 bar, while the testing pressure for FCI seems to be 1 bar