Disconnecting oxygen gauge line in Bravo

[IvanP]

I found a minor leak by the oxygen pressure gauge in the cabin and I may need to disconnect the line that goes from the tank to the gauge to fix it. Can this line be disconnected from the valve without having the empty the tank first? My tank is almost full. The tank has Scott valve p/n 803216-03.

Thanks in advance for any suggestions. 

[Falcon Man]

If the Oxygen valve in the cabin is turned off you can remove the gauge after removing the side panels. The leak usually is where the O2 line comes into the gauge. There is no need to disconnect the line in the tail if the leak is in the cabin, unless you suspect the tubing is broken, then you may be able to repair it in the cabin.

[IvanP]

The tubing is fine, the leak is in the thread on the gauge. Probably just needs to be tightened, but the line to the gauge is pressurized even if the valve is in off position and I would prefer not to be playing with the fitting while under 1500PSI.  

[Fly Boomer]

1 hour ago, Falcon Man said:

If the Oxygen valve in the cabin is turned off you can remove the gauge after removing the side panels. The leak usually is where the O2 line comes into the gauge. There is no need to disconnect the line in the tail if the leak is in the cabin, unless you suspect the tubing is broken, then you may be able to repair it in the cabin.

That suggests that in your 252, with the cabin control in the "off" position, the gauge is not showing tank pressure.  And only when the cabin control is moved to the "on" position will the gauge register tank pressure.

Do I have that right?

 

[Falcon Man]

Correct

[Ragsf15e]

1 hour ago, Fly Boomer said:

That suggests that in your 252, with the cabin control in the "off" position, the gauge is not showing tank pressure.  And only when the cabin control is moved to the "on" position will the gauge register tank pressure.

Do I have that right?

 

That seems weird, because that line is pressurized in mine no matter where the on/off is.  Sounds like yours is like mine - the high pressure line is always on?

[cliffy]

Is there no shut off valve on the bottle itself?   First thought- but-

In checking the Service Manual (Chapter 35 of the M manual available right here on MS) it appears that the gauge is incorporated into the valve on the tank itself and may not be able to be separated on a full tank. The IPC isn't too good at depicting what the actual connection is. 

I would think that if the actuation lever is turned off and the bottle pressure goes down over time (showing a leak) that the gauge is in direct connection to the bottle and can't be removed on a full bottle. 

Recommend going into the Ch 35 and reviewing O2 procedures if you are not fully conversant with them. 

[Falcon Man]

Oops - I was wrong on that last question. The cabin control turns off the valve at the regulator. The line is still pressurized to the O2 ports and gauge. If you intend to remove the gauge from the supply line to inspect the source of the leak you can depressurize it by plugging in a regular O2 cannula connector and open up the needle valve. At least that is how the system is hooked up in a K model. Sorry!

[IvanP]

Based on the IPC, the service manual, and inspection of the system in the plane, the line to the gauge is always pressurized and connected to the fill port. There is no shut-off on the bottle itself, other than the valve that opens the flow to the cabin ports. When reading the service manual, I get the impression that the bottle can be disconnected without emptying. Seems that there may be a Schrader valve in the fitting that goes from the fill port to the valve. I was hoping that some MS members may have personal experience with this set up. 

[buddy]

12 hours ago, IvanP said:

I found a minor leak by the oxygen pressure gauge in the cabin and I may need to disconnect the line that goes from the tank to the gauge to fix it. Can this line be disconnected from the valve without having the empty the tank first? My tank is almost full. The tank has Scott valve p/n 803216-03.

Thanks in advance for any suggestions. 

Yes you can disconnect the line on the valve and that will disconnect the pressure without emptying the tank. Make sure that the small O ring on the line does not get damaged before connecting the line back into the valve.

[Fly Boomer]

17 hours ago, Ragsf15e said:

That seems weird, because that line is pressurized in mine no matter where the on/off is.  Sounds like yours is like mine - the high pressure line is always on?

Until this thread, I thought (assumed) that the gauge showed tank pressure at all times.  I guess this assumption was based on the fact that the gauge doesn't go down even if the oxygen hasn't been used for an extended period.  But it may mean that there are no leaks in the gauge circuit, and it just continues to show whatever pressure it last saw when the oxygen control was on.

[IvanP]

9 hours ago, buddy said:

Yes you can disconnect the line on the valve and that will disconnect the pressure without emptying the tank. Make sure that the small O ring on the line does not get damaged before connecting the line back into the valve.

Thank you.

[Fly Boomer]

10 hours ago, buddy said:

Yes you can disconnect the line on the valve and that will disconnect the pressure without emptying the tank. Make sure that the small O ring on the line does not get damaged before connecting the line back into the valve.

If the oxygen systems on the 252 and yours are the same, your observation would mean that I could replace my gauge without losing tank pressure?  Are you aware of detailed documentation for the oxygen system?

[BillySpace]

I’d recommend venting the tank first before disconnecting that line, especially since it’s almost full. Even if the valve is shut, there could still be some pressure. Better to be safe than sorry.

[MikeOH]

I've been trying to follow this thread without success!

I cannot believe the tank itself does NOT have a shutoff valve!

Am I to understand that the ONLY way to fill the tank is through the external fill port?  It seems an incredibly dumb design where the stored O2 cannot be cutoff from the rest of the system.  It implies the ONLY way to de-pressurize the system is to vent the tank!  Really???

What am I missing?

[Fritz1]

I had a similar leak in my Bravo, very slow, right at the gauge, found with water throwing bubbles, tightening the fitting just at tad fixed the leak, no leak since and that was 3 or 4 years ago, have an O2 tank on a cart in my hangar which I treat with great respect, annual rental costs about as much as refilling the tank, use one or two tanks per year, swap them when they are down to 700 psi, main reason for having tank is that FBO usually bent my O2 door, financially owning the tank and the equipment is a wash at best at the slow rate that I am using tanks

[IvanP]

20 minutes ago, Fritz1 said:

I had a similar leak in my Bravo, very slow, right at the gauge, found with water throwing bubbles, tightening the fitting just at tad fixed the leak, no leak since and that was 3 or 4 years ago, have an O2 tank on a cart in my hangar which I treat with great respect, annual rental costs about as much as refilling the tank, use one or two tanks per year, swap them when they are down to 700 psi, main reason for having tank is that FBO usually bent my O2 door, financially owning the tank and the equipment is a wash at best at the slow rate that I am using tanks

I am considering getting a hangar set up as well once I fix the leak. It is not much, but still annoying. The fill port access is not very well designed and I had to change the fill port in the past.  Fortunately, my local FBO guys are nice enough to bring the O2 cart to my hangar when I need a fill and I will connect the hose to the port myself. That way, I can only blame myself if the port gets messed up again. 

[kortopates]

Until this thread, I thought (assumed) that the gauge showed tank pressure at all times.  I guess this assumption was based on the fact that the gauge doesn't go down even if the oxygen hasn't been used for an extended period.  But it may mean that there are no leaks in the gauge circuit, and it just continues to show whatever pressure it last saw when the oxygen control was on.

You assumed correctly - the gauge is always under pressure but removing the line is not an issue since there is a schrader like valve on the regulator HP port just like the Scott input port. there is a lot of misinformation in this thread, but mostly corrected. Everything needed is in the MM.


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[kortopates]

On 4/16/2025 at 7:05 PM, MikeOH said:

I've been trying to follow this thread without success!

I cannot believe the tank itself does NOT have a shutoff valve!

Am I to understand that the ONLY way to fill the tank is through the external fill port?  It seems an incredibly dumb design where the stored O2 cannot be cutoff from the rest of the system.  It implies the ONLY way to de-pressurize the system is to vent the tank!  Really???

What am I missing?

The regulator on the tank has a valve to open and close. Its the same valve that is wired to the cockpit to turn on and off the flow of O2.

Its a built-in tank so an external port is installed at the fuselage inside of an access door, much like a APU port, which is used to fill the tank. The tank can be removed and re-installed without losing any gas/pressure or without depressurizing. But its only removed when its needs a hydro or replacement.

Really about the only time its depressurized is when it needs to be hydro'd or to pull off the regulator or it needs to be shipped. Once its totally depressurized its needs to be cleaned before re-filling.

[IvanP]

Thank you Paul for your explantion. I removed the line without any issues - as you said, there is a schrader valve in the fittig and there is no need to empty the tank for disconnecting the gauge.

Edited April 20 by IvanP

[kortopates]

Excellent, it’s a great idea to replace the small o-ring there just so you’ll only need
to put the line back on once and be leak free.


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[IvanP]

15 hours ago, kortopates said:

Excellent, it’s a great idea to replace the small o-ring there just so you’ll only need
to put the line back on once and be leak free.


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Good idea. Do you by chance know the specs for the O-ring. I could not find it in the IPC or MM.

Thanks.

[buddy]

Ivan, I got the “0” rings from Master Air Parts, inc. I spoke to Miguel Gomez (805)928-2929. If I remember right he just sent me a couple of “0” rings with the lube free of charge a few years ago.

Buddy

[M20F]

This all sounds pretty stressful.  My suggestion is light up a Marlboro and then get back at looking for that leak.  It could lead to a eureka moment.