I would like to draw your attention on the EN 1779 standard (dated August 1999, as far as I know) about  Non-destructive testing  -  Leak testing  -  Criteria for method and technique selection.

         In particular, in paragraph 6 (page 4, last sentence), it is stated that:
                  "... Zero leakage rate shall not be specified.
                   The required leak tightness shall be related to the function of the object under consideration..."

         What's your opinion about that?

Clarify the scope or application of EN 1779.  I don't have a copy.  The title is "Non-destructive testing - Leak testing - Criteria for method and technique selection."  Does the leakage criteria apply to flange leakage - associated with helium leak detection?

        The mentioned standard is intended for general purposes and "describes criteria for the selection of the most suitable method and technique for the assessment of leak tightness by indication and measurement of a gas leakage".
        Some of those methods and techniques are: vacuum hood or chamber, chemical detection with detection, tracer gas (usually helium), vacuum box, sniffing (with helium or halogen), pressure change (rise or decay), bubble tests, flow-metering, etc...

        In any case, I was only trying to focus the discussion about the "ZERO LEAKAGE" expression which (if not further defined) represents only a dangerous marketing concept, with no technical and/or scientific meaning.
        In addition, many other issues may be involved: such as the measurement accuracy concept (just to mention one) which seems to be ignored by everybody, Engineers and Specifiers included, in the valve world/Balance Valves!!

     winky smile

        But this is my opinion... and, as I said before, I wanted to hear about the other Members' ones!

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