Finding O2 leak

[milotron]

Hey folks,

After my last annual, my M20K came back with a fairly slow leak in the built in O2 system. It leaks down slowly even with the main valve closed. It was dropping faster at higher pressures, but has slowed down now under 1000 psi.

Any hints on finding the leak? Is it as simple as using a soap solution on all the joints and looking for the bubbles or are the better options?

 

Thanks,

[EricJ]

2 minutes ago, milotron said:

Hey folks,

After my last annual, my M20K came back with a fairly slow leak in the built in O2 system. It leaks down slowly even with the main valve closed. It was dropping faster at higher pressures, but has slowed down now under 1000 psi.

Any hints on finding the leak? Is it as simple as using a soap solution on all the joints and looking for the bubbles or are the better options?

 

Thanks,

Soap isn't recommended due to potential contamination/corrosion and volatility issues.   The bubble method does work well you just have to use something that's okay for O2, like this:

https://www.aircraftspruce.com/catalog/appages/detectorfluid08-12291.php

 

Edited June 13, 2020 by EricJ

[milotron]

thanks Eric. I appreciate the advice. I added it to my next spruce order.

[kortopates]

Was the bottle removed at last annual for a hydro? If so I would start there with the two connections. The HP connection uses a small o-ring. If not replaced (see logs) then that would be a likely cause.

[milotron]

1 minute ago, kortopates said:

Was the bottle removed at last annual for a hydro? If so I would start there with the two connections. The HP connection uses a small o-ring. If not replaced (see logs) then that would be a likely cause.

No, bottle was done in 2019 and was fine last year.

I am suspecting something around the gauge in the pilot side panel as the shop had it off for some reason...could be the gauge too I suppose.

[kortopates]

Just now, milotron said:

No, bottle was done in 2019 and was fine last year.

I am suspecting something around the gauge in the pilot side panel as the shop had it off for some reason...could be the gauge too I suppose.

Be sure to check the fill portal - easy to verify and very common leak source. Gauge area is very rare since it isn't disturbed.

[milotron]

I will do that also. That one seems easiest as nothing to disassemble!

 

I'll add those o rings to the spruce order also.

 

[khedrei]

I wont argue with the soap issue but simply say this. The O2 goes out, not in. So anything on the lines will not be sucked inside but pushed outside.  All my lines and fittings are copper.  Same as your water pipes at home. I sprayed mine with an all purpose cleaner to find the leak then used a bottle of water to spray and rinse off the soap. Tightened up the fittings and tested again. If 1800PSI air isnt coming out then ambient psi liquid isnt going in. That being said using the approved product is probably your best bet. 

[Andy95W]

The problem isn't where the air goes, it's what the oxygen reacts with.  Any type of oil exposed to pure oxygen will oxidize- i.e., burn.  If you're 100% sure the soap has absolutely zero oil products in it, no problem.  If not, yikes.

[larryb]

It could be anywhere. I found and fixed 3 separate leaks to get my system tight. The last one was the hardest, the valve was leaking internally even while closed. And yes, the cable was properly adjusted. Required a valve overhaul to fix.

[carusoam]

The O2 system can wear, age, and get holes poked into it...

Parts can get replaced with non-conforming bits and pieces...

Compression fittings aren’t well known by everybody...

I did a search on my favorite leak detector...  Snoop....

https://mooneyspace.com/search/?q=Snoop&quick=1

This search just uncovers a few threads of similar Mooniacs with the same challenge...
 

+1 regarding O2 in contact with oil or grease... it can really start a fire without an outside resource of energy... no spark required...

Best regards,

-a-

[philiplane]

the check valve inside the filler port can develop cracks from age. Leak check the fill port after installing the cap. Most of the caps are not bubble tight

Edited June 13, 2020 by philiplane

[EricJ]

2 hours ago, Andy95W said:

The problem isn't where the air goes, it's what the oxygen reacts with.  Any type of oil exposed to pure oxygen will oxidize- i.e., burn.  If you're 100% sure the soap has absolutely zero oil products in it, no problem.  If not, yikes.

Yes, it turns out that oxygen is a very efficient oxidizer.   Who knew? 

[chrisk]

My previous annual had the O2 bottle removed for a hydro test.  Some time after, a leak showed up. 

To find the leak,  I filled the O2 bottle in the plane, then ran my hand along the lines.  I could feel the air leak.  It was the fitting on the back side of the O2 fill port.  It must have been disturbed when the bottle was removed.

[Jerry 5TJ]

3 hours ago, chrisk said:

To find the leak,  I filled the O2 bottle in the plane, then ran my hand along the lines.  I could feel the air leak. 

Searching for a 2000 psi leak by running your hands over the bottle or hose definitely is not recommended.  
 

[chrisk]

5 hours ago, Jerry 5TJ said:

Searching for a 2000 psi leak by running your hands over the bottle or hose definitely is not recommended.  
 

In fairness, the leak was small and I didn't tightly grab the O2 lines, which are relatively small, maybe 1/8th inch.  But you point is taken, a large leak could be dangerous at 2000 psi.  --But you could probably find a large leak easily by sound alone.  

[khedrei]

Not all the lines are at 2000 psi. The ones after the regulator are not. But the fitting at the fill port would be I think. 

[larryb]

My leaks were:

Fill port. Previous mechanic over tightened fitting crushing compression fitting. Cut off and replaced compression fitting.

O-ring fill port at valve. 20 years old, dry and stiff.

Tank valve needed overhaul.