Leak Test Help..

[Ace1985]

We've got an issue with one of our leak test sequences in work.

Here's the set up:

Main pressure - regulated - leak tester - leak tight valve (plc operated) - sealed face - welder injection moulded bottle.

After every break or at start up, we get a leak fail. When re-tested, the bottle passes and will run as expected (usually 100% efficient, give or take the odd iffy weld). It's as if the pressure build up is effecting the test somehow.

We've replaced the reg, leak tight valve, tried a like for like leak tester in there, no joy. All bungs, pipework and fittings are fine.

The leak test is an 80mbar test, decay test. So prefill of pressure to fill the volume of the bottle, fill to set point, take a measurement, stabilise for a set time, take a measurement, then result based on our set tollerances.

It's really stumping us to why, after a 10 min or so idle time, EVERY next bottle will fail the first test.

Suggestions welcome.

 

[Compositepro]

Perhaps it because gas gets cooler when it is expanded through a pressure regulator. Repetitive testing allows the tubes to the bottle to cool so that test gas will tend to expand slightly in the bottle as it warms. This will cancel the slight pressure loss of the bottle expanding from pressure increase (a creep effect).

For the first test after idle time, the tubing to the bottle has not reached an equilibrium temperature.

 

[IceStationZebra]

You didn't state what volume constitutes a "leak" but could it be that a hose or some other component is taking a set? During the 10 minute break it could relax back to its natural shape, then during the first test is deforms causing a false reading?

Slim chance, but a thought.

ISZ