Air brake union woes

[larry5b6]

I've been chasing a slow air leak in the braking system of our 2012 Tiffen Allegro Breeze for some time now. The system easily passes the widely circulated brake test checklist, so I'm not worried, but it bleeds down to zero in about 2 days of sitting, which it didn't used to do.

After much hair-pulling, I identified the source of the leak as two 1/4" push-in unions under the instrument panel, that connect a pair of 1/4-inch lines to the sensors for the panel air gauges. I've replaced the unions, trimming the tubing to provide a fresh 'bite' area, but I can still hear a quiet hiss (with an electronic stethoscope), coming from that area.

I've ordered a new pair of unions, this time from a truck supply place rather than a random vendor on Amazon, in the hope that it will clear the problem. But I had a couple of questions:

Is there any trick to these besides making sure the tubing has a clean, square cut? I used an 'official' tubing cutter to do the trimming.

Is there any compound or treatment that can be applied to the tubing to improve the seal? The sensors terminate in a short black tube that can't be trimmed and might possibly be treated with something - I can see a shininess reflecting in the flashlight.

Any suggestions would be welcome.

[Ray,IN]

The push-to-connect fittings have a "O" ring inside to seal the end of the tubing. If it is hardened or misshapen it cannot seal properly. There are several videos of how to replace the "O"ring.

[FIRE UP]

larry56b,
Just wondering, have you sprayed any soap and water solution on any fittings or your suspected areas to see any bubbles? That would pinpoint the actual leaks. I've done a little messing around with those push-to-connect fittings on our '04 Horizon 36GD with the CAT C-7 330HP and so far, I've not had any troublesome areas/fittings/joints. To the best of my knowledge, no, do not use any form of sealing compound or solution on any of those type fittings.

Just the square cut and clean surfaces that you're using is all I've done and so far, no issues.
Scott

[sandwip]

I would definitely soap the connections to make sure they are the cause. Gauges have been known to fail internally, rare but I have seen it. Good luck

[jacwjames]

There was a recent post on an RV forum (not sure if it was this one) of an individual who was chasing leaks. He ordered PTC fittings from two different sources that did not work. Turns out the ones that didn't work were out of spec. So making sure you get quality fittings is important.



I went through my air system and the only problem I had was one PTC fitting, the tubing was coming in at an angle. I ultimately used a compression type fitting on this one location to solve my problem.

[larry5b6]

Thanks everyone for you suggestions. The location of the unions is such that the soapy water test would be... challenging - I'd need a piece of tubing to get the water up there and probably my borescope to see the bubbles, and I'd surely wind up with soapy water in my eyes. The approach I used instead was to listen with headphones and a sensitive microphone - and the hissing noise is very definitely coming from the unions.

The gauges are not the issue - they're at the other end of several feet of wire from the sensors, which are pushed into the union. The sensors themselves don't seem to be leaking.

jacwjames comment about fittings being out of spec was enlightening. Hopefully that will be my problem and the new fittings arriving this week will work better than the first replacements I ordered. Those are still in the return window at Amazon, and if the new ones fixe the problem they're definitely going back.

[Sherpa Vern]

Originally Posted by sandwip

I would definitely soap the connections to make sure they are the cause. Gauges have been known to fail internally, rare but I have seen it. Good luck

Rare as it may be, I had an air gauge leak a few years ago.