Quote Originally Posted by Aimstraight View Post
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.
I can't remember asking to be honest. I had assumed it was the neck thread, but thinking of it.

Yes, I've seen thread stretch on airgun cylinders which are screwed on and off with pressure in the cylinder because the pressure releases before it is all the way home. So it could very well happen on the outlet under certain circumstances. I would say that's a definited concern if they are using spacers to seal 200 bar adapters in 300 bar bottles... this means there's less threads engaged and therefore more pressure per thread, and therefore force per thread which could make them stretch perhaps.

The threads on the outlet are fairly common, DIN. There's some 232 neck threads which are less common now and the heads are no longer made... I know this because we were warned about it when I last filled, if the threads go the bottle is shagged because they can't get a new head to fit.

The go-no-go is something that appears to be recent and differs from tests abroad. I saw it mentioned in some technical article when people were having arguements about testing here vs abroad.

I really get why people aren't happy when a bottle fails. But why reach for the conspiracy handle when it's just a simple test for your safety? Why would a shop risk pissing you off over £10-20 to them when you'd be doing that a year in fills for the next 5-10 years plus whatever else you spend there...?