On/off valves leakage class standard

[prajule]

The three most commonly used for valve leakage are:

API (American Petroleum Institute) 598 – this document covers valves of all types, metal and soft seated, and is the industrial valve seat leakage baseline.
FCI (Fluid Controls Institute) 70-2 (also called ANSI/FCI 70-2) – this document is specifically for control valves, and in general allows higher leakage as a result.
MSS (Manufacturer’s Standardization Society) SP-61 – this document is similar to API 598 in that it applies to metal and soft seated valves. For soft seated valves, it converges with API 598, while for metal seated valves it may allow a little more leakage than API 598 would.

In general, specifications such as API 598 or MSS SP-61 that govern leakage for soft seated valves call for ‘0’ bubbles of air or ‘0’ drops of water under the specified test conditions over the minimum test time period. These valves are therefore sometimes referred to as ‘zero leakage’ valves. In reality, there really is no such thing as ‘zero’ leakage, since microscopic amounts of material may indeed cross the seat or packing boundaries, especially if helium or hydrogen or other small molecule gases are used. Another common term for soft seated valves is ‘bubble tight’.

Less frequently, the leakage performance for soft seated valves is referred to as Class VI, which is the tightest leakage under FCI 70-2, and generally applies to resilient seated control valves (as opposed to metal seated control valves or soft seated shut off valves). In fact, FCI 70-2 Class VI allows some small number of bubbles per minute, increasing with valve size, during the test, whereas API 598 and MSS SP-61 do not.

Metal seated valves, on the other hand, usually (not always) have some level of acceptable leakage when tested, defined first as some acceptable amount of liquid, under test conditions and over the time period of the test. Gas is an alternate test media for metal seated valves, as liquid can be easier to measure, especially for larger valves.

[aidini]

Thank you for the information.
What would you prefer to be referred to as the leakage standard when filling on-off valves data sheet?

[aidini]

Thank you for the information.
What would you prefer to be referred to as the leakage standard when filling on-off valves data sheet?

[inconel]

Thanks

[Xiphos]

when zero leakage / tight shut-off needed, API 598 should be applied;
when leakage permitted, ANSI/FCI 70-2 Class X or ISO 5208 Rate X can be used......