nraheja,

Thanks for the feedback. That is a very interesting fact that I have not heard before. How long ago did you get your PST air trap ?

I have had 6 PST air trap so far and no problem at all.
I'll have a look at the 2 spare ones I have at the workshop to see if I can pinpoint your problem.

However I am sure about one thing: on my air traps the aluminium assembly end is so tight ( o ring seal clearance minimal ) that it needs large pliers to get removed from the bottle. No possibility of an air leak on that side.
By the way, if you remove the aluminium assembly, I strongly advise to fit it back with a good load of silicon grease on the o'ring.
Just to confirm as well, the plastic cap is not here to seal the bottle, but just to hold the aluminium assembly in place.



On this picture you can see the large black o'ring. That's the one that does the sealing job.
If the o'ring is not tight enough to get a proper sealing effect, just wrap one or two turns of Teflon plumbing tape in the ring groove...