Dive Bottle Test - Short & Curly's?

[Aimstraight]

..... Threads fail. I’ve had one go on a bottle that was only on its 2nd test. Same deal.....

Out of interest was that the DIN outlet?

Think it would do us all a favour if the OP asks the test centre to confirm where in the BS/EN procedures it requires this test. I looked on the SITA website and the various downloads are scant in detail (deliberately so as to have to buy the BS/EN to find out), it just refers to 'valve threads' and cylinder threads. So for an airgun valve do they also test the thread for the gauge? All this would be useful to know, as we are paying for the service, it should be transparent. Good to know if all centres do check all threads (I doubt it somehow, the guage threads can differ on valves).

Would it be possible for the DIN outlet threads to be comprised by silicone grease (from an o-ring seal)? Not suggesting that here, but just wondering. Probably many other potential causes including dirty threads, excess force, marginal production tolerance, poor thread on mating parts, test centre handling.

Presumably when a cylinder is filled to 300 bar, the connection is tight enough (but not excessive) to compress the interface o-ring, and then the 300 bar pressure on the face of the connectors is transferred through the threads. Similarly when filling an airgun from the cylinder. Hence all mating threads need to be in very good condition/very well matched.