Marian Krzymiński May 15, 2013:

bubble-tight A commonly used term to describe the ability of a control valve or regulator to shut off completely against any pressure on any fluid. Unfortunately, it is completely unrealistic. Control valves are tested to ANSI B16. 104 and FCI 70-2-1976 which is the American National Standard for Control Valve Seat Leakage. This standard uses 6 different classifications to describe the valves seat leakage capabilities. The most stringent of these is Class VI which allows a number of bubbles per minute leakage, depending on the port size of the valve.

tadeusz50 May 14, 2013:

znalazłem na google taką wymianę zdań, może to pomoże:
monaco8774 (Petroleum)
Bubble tight means different things to different people, if your buying a valve from these guys specify the test you want to conform to there are several classifications that are used for valve tests as you have mentioned. Go back and have them confirm they conform to your requirements. That said my experience is bubble tight is synonomous with class V test level (but it wouldnt stand up in a court).

zdas04 (Mechanical)
The term "bubble tight seal" is very old. My understanding is that it originated from a test where a valve was installed in an air system with an open end pointing up. Some soap was poured into the open end and air was applied to the other side. The valve passed if no bubbles formed in the soap. I'm not sure if this is true or not, but it was the only explanation I ever heard that was at least plausible.