Bailout cylinder and pillar valve compatibility failure

The incident occurred during visual inspection of bailout cylinders, when it was identified that six out of the twelve pillar valves tested, with GO/NO-GO thread gauges, failed the GO thread gauge test. 

Of the six cylinders that passed the original test, four cylinders were rechecked at the next six-monthly planned maintenance check, and two of the pillar valves failed the GO gauge thread test.  A possible cause of the later failure may have been wear and tear, continual emptying and recharging to 200 bar (at 200 bar there is almost 1 tonne of force on the pillar valve).

Our member has introduced a quality check of cylinder threads and pillar valves whereby GO/NO-GO thread gauges are used before accepting any new stock.  When recently purchasing new cylinders and additional pillar valves the pre-acceptance tests were performed.  It was identified that there was a surprisingly high failure rate when testing the new pillar valves.  Of six pillar valves purchased, four failed the GO thread gauge test.  It is to be noted that similar failure rate has also been the case with subsequent purchases of pillar valves.

Attached are photographs of both the six pillar valves which failed during the original test and two other, order replacement pillar valves which also failed the test.  Also attached are photos of a new pillar valve with packaging and demonstration photos of successful & unsuccessful GO thread gauge tests.

All tests were conducted by a technician who is qualified as an “ASSET” Part 1 & Part 2 Cylinder Inspector using recently calibrated GO/NO-GO thread gauges.

GO or NO-GO thread ring gauge – A thread RING gauge is used to check the accuracy of an outside thread. The GO thread ring gauge should easily and completely slide over the outside thread. The NO-GO thread ring gauge should not be able to slide over more than three threads - if it does, the outside thread is too small.

GO or NO-GO thread plug gauge – A thread PLUG gauge is used to check the accuracy of a threaded hole. The longer end of the tool will be the GO end, while the shorter end is NO-GO. The longer end should be able to thread into the threaded hole easily and completely. If not the hole is too small. The NO-GO end should not enter beyond the third thread - if it does, the threaded hole is too large.