O2 Problem

[Davidv]

I thought I’d put this issue out there to see if the collective wisdom/experience of this group could help me solve this O2 issue on my 92 Bravo.
 

Last December when flying from FXE to Boston I landed and heard this “hissing” noise coming from the oxygen bottle area (once I got out of the plane).  I had been flying at FL210 and it had been working fine but possibly depleting faster than normal. I thought I had some sort of leak so refilled the bottle when I got back home.  The pressure actually held fine on the ground and in the air.  The only time when it would draw down at a crazy rate is when the valve was turned on (500 psi in 30 mins).

At annual in March I had the bottle hydro tested (it was due) and the regulator overhauled.  Looking at the work order they did find some issues with the regulator and supposedly fixed them.  I flew the plane a few times after annual up high and the problem seemed to be fixed (although the oxygen was drawing down still a little quicker than before I had an issue).

Last night I was flying from Dallas to FXE at FL210 and my oxygen went from 1000 psi to 0 in about an hour.  Once it got to 500 it went very quick.  This was especially frustrating since I had a 65 knot tailwind and was smooth sailing at 265 over the ground and now had to go low.  You can imagine my audible frustration in the cockpit :).

Of course I’m going to track this down with my mechanic and shop that did the regulator overhaul but anyone have something similar happen?

[LANCECASPER]

Have you checked the line and fittings that go up to the gauge?

[Davidv]

13 minutes ago, LANCECASPER said:

Have you checked the line and fittings that go up to the gauge?

No, I think that has to be next, just very odd that it holds when the valve is turned off.  I would think if the problem was in the line it would leak out when off too, but maybe you have a better idea of how the system works?

[A64Pilot]

The valve should be a high pressure valve, that is they usually isolate the tank from everything else, and a leaking tank is very unusual but possible I guess where the valve threads into the tank.

Sometimes the tank pressure gauge  is before the valve so tank pressure is always displayed, even with the system off.

‘ A leak is easy to find, it’s accessing the system if it’s a built in that may be difficult.

‘Soapy water is likely safe and OK, but I would advise to use the special leak detection fluid for O2 systems, yes it’s just soapy water, but it’s safe soap. My luck if I didn’t I’d  find some kind of soap that had oil in it.

But usually it’s the tank with a valve connected directly to it, and the regulator connected to that valve, after the reg of course it’s low pressure. If it leaks only when the system is on, then it’s most likely a low pressure leak or the regulator itself of course, maybe they left a fitting to the reg loose?

Edited April 9, 2021 by A64Pilot

[N201MKTurbo]

You say it only leaks down when the O2 is turned on. So the leak is somewhere in the distribution system down stream of the regulator. To leak down that fast it has to be a gross leak. perhaps one of your ports isn't closing. You can test them by turning on the oxygen and put your finger over the hole and see if any pressure builds under your finger. otherwise you will need to pull your interior to inspect all the tubes and fittings.

For Leak checking Swagelok Snoop is the best stuff.

https://www.swagelok.com/en/product/leak-detectors-lubricants-sealants/snoop-liquid-leak-detector

 

[philiplane]

Always look at areas where recent work has been done. Sidewalls have to come out for avionics work, and oxygen ports may not be tightened correctly afterwards. Plumbing down stream of the regulator has a large leak, so it's more than a finger tight low pressure fitting. Or, the regulator itself has a leak when turned on.

[anthonydesmet]

On 4/9/2021 at 11:29 AM, N201MKTurbo said:

You say it only leaks down when the O2 is turned on. So the leak is somewhere in the distribution system down stream of the regulator. To leak down that fast it has to be a gross leak. perhaps one of your ports isn't closing. You can test them by turning on the oxygen and put your finger over the hole and see if any pressure builds under your finger. otherwise you will need to pull your interior to inspect all the tubes and fittings.

For Leak checking Swagelok Snoop is the best stuff.

https://www.swagelok.com/en/product/leak-detectors-lubricants-sealants/snoop-liquid-leak-detector

 

201MKT has it right.  Your bottle and regulator are fine.  Most likely place might be at the gauge. May have a crack at the gauge....my hanger neighbor had this.  Other possibilities are:

- check your fitting at the connection...cracks in your hose, your connector not engaging properly - air blowing past the connection.

- do you just have your O2 connected or do you also keep copilots O2 connected....valv might be open

- when you say it went from 1000 to 0 did you still have good flow?...I had a guage that showed 0 and I had good flow for about an hour when I found my gauge was cracked.

but in any case from your discretion it’s not the bottle or regulator.......definitely down stream.....may have to pull some interior panels but before you do definitely check your fittings and work back from there.....

also calling @DonMuncywho is an expert at O2.....

[Davidv]

Thanks @philiplane@N201MKTurbo @anthonydesmet

To answer some of your questions, I did have avionics work done about 5 months ago and they most likely had the entire interior out of the plane.  It's possible that they could have hit a fitting.  The odd part is that after I got my regulator back from overhaul everything seemed to work ok for about 15 hours until the episode on this last flight when it started losing about 100 psi every 5-10 minutes once it got past 1000 psi.  I didn't keep the 02 flowing when I was up high because I didn't want it to get to 0 while I was at FL210.  I suppose I could have kept it flowing when I was lower to see if it was a gauge issue but didn't think to try for whatever reason (maybe hypoxia? :)).  When I got back to my hangar I refilled the bottle to about 1100 (couldn't get it higher than that), turned on the oxygen full blast while on the ground and it didn't seem to do much in about 5 minutes on the ground.  I went back to check a few days later and it's still holding at 1100.

Maybe the next step is removing some interior panels and using that leak detector...

[carusoam]

Around here we have seen everything from mismatched fittings to a sheet metal screw penetrating a piece of tubing...

Search the word Snoop for other discussions looking for leaks...

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

Best regards,

-a-

[irishpilot]

soapy water and a spray bottle are your friends. Turn the valve on and start at the bottle and work your way forward.

[A64Pilot]

I use soapy water and a brush, or an eye dropper. Idea is to not have any bubbles, any bubbles means a leak, if you were careful with a spray bottle I’m sure that would work, just dribble the liquid out

[Ragsf15e]

And while you’re using the soapy water inside the cabin, try not to leave the steel tubes, spar or other expensive things real wet and covered with carpet, tape, etc... 

[Warren]

Careful with soapy water!  Some soaps have hydrocarbon and/or components that are flammable in pure oxygen.  There are leak detectors specifically designed to be safe with oxygen systems.  Aircraft spruce carries it — probably worth a few dollars just to be safe.

[RJBrown]

If you do a lot of your flying high enough to need oxygen you need a back up. The Rocket had factory on board oxygen. I always carried the portable system with me.

3 reasons to have a portable system in addition to the factory system.

#1 as above, any problem with the factory system.

#2 oxygen is not always available where or when you travel. I refueled in Dallas on Love field one Sunday. No one was in the shop, I could see the refill bottles, they refused to allow me to refill. 
 

#3 more people use more oxygen. 1 system for me and one system for passengers. I can control My oxygen without others compromising my ability to be alert.

As the pilot I need to be awake and alert. A sleepy passenger or one with a headache won’t kill us all. On the trip from Florida to Colorado through Texas mentioned above the passengers ran out. I did not. 

In the MSE I never planned to need oxygen. The portable was the backup. It backed up my plan to stay low. It gave me choices I otherwise would not have had.

A very early example for me. Flying a rental turbo arrow from Flagstaff to Denver. I had my portable oxygen but expected not to use it. The clouds slowly kept getting higher and I was staying above them. That day I learned my early hypoxia symptoms. They are insidious, slowly climbing took away my mental edge, I forgot the oxygen. I started feeling sick to my stomach. It took me a bit to figure out I was starting to get hypoxia. I was able to turn on the 02, because I had it.

[Davidv]

Well I think my issue may be solved and it turns out it could have been user error.  Apparently the regulator has a shuttle valve that either needs to be completely open or completely closed.  When it's halfway open it dumps O2 right out of the regulator.  Brian Kendrick (many thanks to him) opened the regulator halfway and said "is this the sound you heard after landing that one day?". Sure enough, the answer was yes. 

Call it conservatism or stupidity, but I got into the habit of turning the regulator knob on the side of the cabin just enough until I saw that oxygen was flowing at the rate I needed.  You need to turn the regulator knob about 270 degrees to get all the way open.  I can't say if my issue is 100% solved since I haven't flown the plane yet, but I'm pretty confident this is the answer.  In any case, I thought I'd let everyone know here since some other very knowledgeable Mooney people also weren't aware of this valve peculiarity.   Hopefully this helps someone in the future who has a similar issue.

[kortopates]

1 hour ago, Davidv said:

Well I think my issue may be solved and it turns out it could have been user error.  Apparently the regulator has a shuttle valve that either needs to be completely open or completely closed.  When it's halfway open it dumps O2 right out of the regulator.  Brian Kendrick (many thanks to him) opened the regulator halfway and said "is this the sound you heard after landing that one day?". Sure enough, the answer was yes. 

Call it conservatism or stupidity, but I got into the habit of turning the regulator knob on the side of the cabin just enough until I saw that oxygen was flowing at the rate I needed.  You need to turn the regulator knob about 270 degrees to get all the way open.  I can't say if my issue is 100% solved since I haven't flown the plane yet, but I'm pretty confident this is the answer.  In any case, I thought I'd let everyone know here since some other very knowledgeable Mooney people also weren't aware of this valve peculiarity.   Hopefully this helps someone in the future who has a similar issue.

Sounds like your not using a flow meter like the Precise Flight A5 Flow Meter shown in the picture here: https://preciseflight.com/product/all-in-one-solo-pack-with-a5-flow-meter/# Which is arguably the best flow meter available. They do sell them without buying their entire solo kit.

The flow meter is the correct "conservatism" approach - which is what its designed to do!

 

 

[Davidv]

Just now, kortopates said:

Sounds like your not using a flow meter like the Precise Flight A5 Flow Meter shown in the picture here: https://preciseflight.com/product/all-in-one-solo-pack-with-a5-flow-meter/# Which is arguably the best flow meter available. They do sell them without buying their entire solo kit.

The flow meter is the correct "conservatism" approach - which is what its designed to do!

 

 

The flowmeter is exactly what I use.  My point above is that when you turn the regulator knob on the airframe just a little bit, the A5 regulator will show full flow of oxygen (with the ball glued to the top).  Instead of turning the knob all the way I would turn it on until my A5 regulator showed full flow of oxygen.  This isn't an issue with the later model mooneys that have the on/off button for oxygen.

[kortopates]

Just now, Davidv said:

The flowmeter is exactly what I use.  My point above is that when you turn the regulator knob on the airframe just a little bit, the A5 regulator will show full flow of oxygen (with the ball glued to the top).  Instead of turning the knob all the way I would turn it on until my A5 regulator showed full flow of oxygen.  This isn't an issue with the later model mooneys that have the on/off button for oxygen.

In that case, I miss understood. I thought you were only partially turning the regualtor knob to just get enough O2 but now I realize that's not very possible without something like a flow meter to tell, without the flow meter you'd have a visual ball in the line that would go from red to green when O2 flows, which was the standard in the days before flow meters. But it didn't give any indication of flow rate - just that O2 was flowing.

I assume you have the Mooney O2 system with the Scott 2-stage regulator versus the later Precise system with a 1 stage regulator. The two stage system has a built-in altitude compensating regulator after the first stage that further reduces O2 delivery from max flow at low altitudes. It was designed to be effective without or before we had flow meters to more precisely adjust flow. But both systems are designed to be fully turned on. 

[carusoam]

Ahhhhh….

Valve types….

Not all valves are capable of throttling flow…

Even though they may seem to…..

That is deep in the engineering handbooks…  See if @Hank has some insight on why the O₂ valve misbehaved when cracked open… (caution this thread is a few days old, I’m late to the party)

Check the procedures… it probably says softly…. Open valve fully….   Without giving a hint to what can happen if you don’t open it all the way…

Best regards,

-a-