Persistently leaking fuel sump valves

[AerostarDriver]

In April I replaced my sumps as one had gotten stuck closed and the o-ring had failed on the other causing fuel to seep on the outside of the sump . I ordered band new MDI F391-53S valves from Chief Aircraft and installed them and they sealed up just fine. After a few uses they started to leak from inside the valve. At the beginning it was almost not noticeable, however it is now causing streaking and noticeable drips on my hangar floor.

Has anyone had a similar experience?

How do you suggest installing them? My A&P suggested using fuel lube, which may be my problem.
SBM20-188A does not specify a torque spec or actual install method for the F391-53S.

[carusoam]

My 65C was known to get stuff stuck in the sump drains…

The sump drain valves are a hand torque kind of item… sealing is a rubber O-ring…  over-torquing is easy, resulting in a snapped part…

Finding the source of that stuff is helpful….

If you catch the the stuff that comes out of the drains… you may be able to identify if it is rust particles….

Some older Mooney models used a non-stainless steel for the fuel necks…

My C was dropping rust particles into the fuel tanks…. It was showing up stuck in the sump drains…

And further downstream in the fuel/water separator…

No rust was visible from the outside… until a hole formed… 

There are plenty of SS versions of the same part… easy to get, if this is your challenge…

PP thoughts only, not a mechanic…

Best regards,

-a-

[ShuRugal]

+1 for particles in the drain preventing a seal.

Hey a GATS jar and open the valve wide to flush out anything sticking on the sealing surfaces.

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[EricJ]

Mine stick occasionally, and it's usually just a matter of poking a sample probe up in there a few times to flush out whatever is holding it open.   Leaks are anywhere from a light stream to a very slow drip that is just enough to make a dye ring on the floor after a few days.     It it has stained around the drain, clean it up with some solvent and make sure it's not the rivets leaking.    I got one of those, too. 

 

[AerostarDriver]

1 hour ago, ShuRugal said:

+1 for particles in the drain preventing a seal.

Hey a GATS jar and open the valve wide to flush out anything sticking on the sealing surfaces.

Sent from my Pixel 3a using Tapatalk
 

 

1 hour ago, EricJ said:

Mine stick occasionally, and it's usually just a matter of poking a sample probe up in there a few times to flush out whatever is holding it open.   Leaks are anywhere from a light stream to a very slow drip that is just enough to make a dye ring on the floor after a few days.     It it has stained around the drain, clean it up with some solvent and make sure it's not the rivets leaking.    I got one of those, too. 

 

I do use a GATS jar and have found that I do occasionally get particulate but I sump until I get a clean sample., this still does not stop the dripping. I do take very liberal samples, I would like to think that this should be enough to flush our whatever is causing them both from sealing.  I am considering replacing the sumps again or at least remove and inspect them. 

[ShuRugal]

Work the valve a few times between full open and closed, sometimes particles get jammed in the stem too tight for rinsing action to be enough.

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[bob865]

It may not be the vales at all.  I had this issue with mine that was happening right around the time I did a reseal on the tanks for other leaks.  When Edison in FL got into it he found the nut plates that hold the drain valve were severely corroded.  Had them replaced as part of the reseal and haven't had an issue since.  

Edited December 2, 2021 by bob865
Found the pics

[Guest]

On 11/28/2021 at 3:40 PM, AerostarDriver said:

In April I replaced my sumps as one had gotten stuck closed and the o-ring had failed on the other causing fuel to seep on the outside of the sump . I ordered band new MDI F391-53S valves from Chief Aircraft and installed them and they sealed up just fine. After a few uses they started to leak from inside the valve. At the beginning it was almost not noticeable, however it is now causing streaking and noticeable drips on my hangar floor.

Has anyone had a similar experience?

How do you suggest installing them? My A&P suggested using fuel lube, which may be my problem.
SBM20-188A does not specify a torque spec or actual install method for the F391-53S.

The SB contains loads of info like torque.  Lubricating the O ring won’t hurt.

Clarence

[jaylw314]

On 11/28/2021 at 1:15 PM, AerostarDriver said:

I do use a GATS jar and have found that I do occasionally get particulate but I sump until I get a clean sample., this still does not stop the dripping. I do take very liberal samples, I would like to think that this should be enough to flush our whatever is causing them both from sealing.  I am considering replacing the sumps again or at least remove and inspect them. 

I had one fantastic day where I had a stubbornly seeping sump valve, so I stuck my sample cup (holds about 12 oz) under and tried to flush it out.  When I let go, the valve stuck open and I had fuel pouring all over the hangar floor.  I found a tupperware tray and stuck it under there, and frantically called my mechanic who didn't answer.  After some running around in circles, I finally found an old wooden pencil that I broke the tip off and jammed it into the valve, so I finally had a moment to think and find a larger container to empty the fuel into.  I took the pencil out and jabbed at the valve with the sample cup for a minute or two, when it finally snapped shut.  At that moment, my mechanic called back.

Since then, the valve hasn't stuck again, and it no longer leaks.  The moral of the story is, it may take a LOT of fuel to flush out the valve  

[ShuRugal]

.  The moral of the story is, it may take a LOT of fuel to flush out the valve  

Less fuel than breaking one off

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[apriav]

I have used compressed air.

Take your fuel cap off, turn air supply down to 5 or 10 psi and blow in the drain.

Anything causing leak gets blown off.

Have a blowgun with rubber tip, and no mess.

[Guest]

8 hours ago, jaylw314 said:

I had one fantastic day where I had a stubbornly seeping sump valve, so I stuck my sample cup (holds about 12 oz) under and tried to flush it out.  When I let go, the valve stuck open and I had fuel pouring all over the hangar floor.  I found a tupperware tray and stuck it under there, and frantically called my mechanic who didn't answer.  After some running around in circles, I finally found an old wooden pencil that I broke the tip off and jammed it into the valve, so I finally had a moment to think and find a larger container to empty the fuel into.  I took the pencil out and jabbed at the valve with the sample cup for a minute or two, when it finally snapped shut.  At that moment, my mechanic called back.

Since then, the valve hasn't stuck again, and it no longer leaks.  The moral of the story is, it may take a LOT of fuel to flush out the valve  

I’m told that a wooden golf T works as well.

Clarence