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Fuel drain valve leak saga


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More pictures of fuel tanks and drains.  The first one is a F391-72 drain valve in a Monroe modified Mooney tank.  Here too the drain valve holes don’t drain from the bottom of the tank.  Toe STC holder says don’t worry “water and contaminates will transfer from the extended tank to the main tank through the transfer tube(which is also not on the ) to the main tank where it will be drained through the incorrect drain valve which is also not on the bottom of the tank.

The drain valve has been overtorqued causing the holes to deform.

Clarence

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3ADE5C2A-A442-4F52-B521-FAED609C97E9.jpeg

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37 minutes ago, M20Doc said:

More pictures of fuel tanks and drains.  The first one is a F391-72 drain valve in a Monroe modified Mooney tank.  Here too the drain valve holes don’t drain from the bottom of the tank.  Toe STC holder says don’t worry “water and contaminates will transfer from the extended tank to the main tank through the transfer tube(which is also not on the ) to the main tank where it will be drained through the incorrect drain valve which is also not on the bottom of the tank.

The drain valve has been overtorqued causing the holes to deform.

Clarence

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The messy sealant application on the drain valve adapter plate shows how a messy application would have plugged the drain holes on a nut plate. Notice the clear drain holes on the -72 drain valve despite the messy sealing.

Edited by Gagarin
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Great discussion...

This horse can’t be beaten enough. :)

Thanks for showing all the great pics.

The stretched holes in the drain are typical of a first timer... changing a drain....

Pull out one drain, insert the new one......and it doesn’t stop leaking until the part is lightly  torqued in place...

The seal is the rubber O-ring... 

More than light torque twist the part at the drain holes... slightly more torque snaps the part in half...

The mechanics clear direction to me was don’t overtorque it...

If there is a torque spec for that (probably is...) it is more like finger tight, then it is Ft-LBs.... we’re only squeezing the piece of rubber enough to deform around surface imperfections...

I probably still don’t have all the details straight...

This is the first time I have seen the rusty nut plate. SS parts didn’t start til long after ‘65...

PP thoughts only, not a mechanic...

+1 on knowing what is at the bottom of your tanks... especially if you know you have leaks at the top...

Best regards,

-a-

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7 hours ago, carusoam said:

Great discussion...

This horse can’t be beaten enough. :)

Thanks for showing all the great pics.

The stretched holes in the drain are typical of a first timer... changing a drain....

Pull out one drain, insert the new one......and it doesn’t stop leaking until the part is lightly  torqued in place...

The seal is the rubber O-ring... 

More than light torque twist the part at the drain holes... slightly more torque snaps the part in half...

The mechanics clear direction to me was don’t overtorque it...

If there is a torque spec for that (probably is...) it is more like finger tight, then it is Ft-LBs.... we’re only squeezing the piece of rubber enough to deform around surface imperfections...

I probably still don’t have all the details straight...

This is the first time I have seen the rusty nut plate. SS parts didn’t start til long after ‘65...

PP thoughts only, not a mechanic...

+1 on knowing what is at the bottom of your tanks... especially if you know you have leaks at the top...

Best regards,

-a-

From SB M20-188A the torque value for the drain valve.

Clarence

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Whenever removing F391-53S drain valve blow air into the drain holes to remove any debris from the tanks. Having the drain holes at the very bottom makes it very susceptible to get clog or jam with debris or sealant causing it to partially open and leak through the drain plunger. This causes a blue circular stain around the plunger.

Edited by Gagarin
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34 minutes ago, Gagarin said:

Whenever removing F391-53S drain valve blow air into the drain holes to remove any debris from the tanks. Having the drain holes at the very bottom makes it very susceptible to get clog or jam with debris or sealant causing it to partially open and leak through the drain plunger. This causes a blue circular stain around the plunger.

My Co-Owner fueled plane and sampled fuel last year.  The drain was dripping and he didn’t address.  I came out to hanger a couple of weeks later and there was a huge sticky blue stain on hanger floor.  Co-Pilot tank...Empty.  Expensive lesson.  Bad valve.  Good to have one of these valves available.  That drain had the circular stain around the plunger as described by Gaga.  Good to know on the torque rating.  Great thread.  These valves by Aviation pricing are pretty reasonable AMU wise...

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18 hours ago, M20Doc said:

At the risk of beating a dead horse even more, I took some pictures of the standard fuel drain valve and the suggested alternate, plus the plate nut which is in the wing tank of many Mooneys. 

In the first picture, the standard(correct) drain valve is on the left, the alternate is on the right and the plate nut is in the center.  Note that the correct valve has holes which align with the arches in the plate nut, this allows water and contaminates to drain off the bottom of the tank.

The alternate valve on the right has drain holes which are above the plate nut and have no means of draining water or contaminates from the bottom of the tank through the arches.  This valve can allow about 3/8” of water and contaminates to collect in the fuel tank never to be drained, hardly and improvement is safety.  Water causes engine failures and corrosion inside your fuel tanks.

The second picture shows the difference in O ring size, the correct O ring should seal against the lower wing skin, the alternate valve will force the O ring into the opening in the lower wing skin.

I hopes this helps.

Clarence

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Thank you for making that clear clearance, it seems that Jose’s “fix” is something to cure a deficient condition to begin with, but what it does is it allows a half a gallon of water to remain in your airplane. I see a pattern of bad advice from him on this form I hope nobody takes his advice and gets themselves killed. 
It’s like a fundamental misunderstanding of basic engineering principles.

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14 hours ago, Gagarin said:

Because they work with brand new Mooneys with no debris in the tanks or reseals. 

Great, and that is how your airplane should be right now, or it’s not airworthy. Because it doesn’t conform to the design. Don’t you understand thatGreat, and that is how your airplane should be right now, or it’s not airworthy. Because it doesn’t conform to the design. Don’t you understand that? 
The solution isn’t to raise the drain holes 3/8” inch above the bottom of the tank. 
But you know what, it’s your design it’s your name on it and the next plane crashes the stuff is all discoverable information and I’m sure the plaintiff’s lawyer is going to use it. So keep talking

Edited by jetdriven
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3 hours ago, jetdriven said:

Great, and that is how your airplane should be right now, or it’s not airworthy. Because it doesn’t conform to the design. Don’t you understand thatGreat, and that is how your airplane should be right now, or it’s not airworthy. Because it doesn’t conform to the design. Don’t you understand that? 
The solution isn’t to raise the drain holes 3/8” inch above the bottom of the tank. 
But you know what, it’s your design it’s your name on it and the next plane crashes the stuff is all discoverable information and I’m sure the plaintiff’s lawyer is going to use it. So keep talking

As an engineer I always consider life cycle deterioration impact on any article I design. Debris accumulation is a form of deterioration just like in exposed high voltage insulators or water plumbing. I think your suggested solution is to remove the fuel tank access panels at every annual and clean any accumulated debris. Just make sure you wear a cap when resealing the panels to keep your hair clean of sealant.

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4 hours ago, jetdriven said:

Thank you for making that clear clearance, it seems that Jose’s “fix” is something to cure a deficient condition to begin with, but what it does is it allows a half a gallon of water to remain in your airplane. I see a pattern of bad advice from him on this form I hope nobody takes his advice and gets themselves killed. 
It’s like a fundamental misunderstanding of basic engineering principles.

Check your math 1/2 gallon of water = 116 cu-in. I always check my numbers with my trusty K&E slide rule.

Edited by Gagarin
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So today at the shop I measured the height of the F391-53SMP plate nut and the height of the F391-72 drain valve.

F391-53SMP plate nut is 0.464” tall, the wing skin is 0.050” for a total of 0.514” the arch in the nut plate is 0.105” tall.

F391-72 valve is 0.510” from the base of the nut to the top of the holes.

With the incorrect part number valve screwed in fully with no other anomaly’s in the skin, there is 0.004”+/- of each hole available for dirt and contaminates to drain through.  This leaves between 7/16” and 1/2” of water in the bottom of the tank that will never be drained.  

Clarence

 

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5 hours ago, Gagarin said:

As an engineer I always consider life cycle deterioration impact on any article I design. Debris accumulation is a form of deterioration just like in exposed high voltage insulators or water plumbing. I think your suggested solution is to remove the fuel tank access panels at every annual and clean any accumulated debris. Just make sure you wear a cap when resealing the panels to keep your hair clean of sealant.

The debris (if any) drains out the fuel valve. And you can unscrew their fuel valve and check the drain holes with a piece of safety wire.  I haven’t had any trash in ten years but what do I know. But also, what does the factory know, they certified it just like that. And your “fix” is bad engineering.  Lift the drain point a half inch and call it good  

and yes a quart a side is 1/2 a gallon.  7/16” x the footprint of the onboard bay X2 is easily that.  
 

where did you get your engineering degree from? 
 

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Leaving that much water, or jet-A, or other contaminants in the tank seems ill-advised to me.    If there's so much sediment and crap in the tank that the drain no longer works, that's a pretty good clue that it needs attention, not a higher drain.

Just my dos centavos, also from an engineer, for whatever that's worth.

 

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13 minutes ago, EricJ said:

Leaving that much water, or jet-A, or other contaminants in the tank seems ill-advised to me.    If there's so much sediment and crap in the tank that the drain no longer works, that's a pretty good clue that it needs attention, not a higher drain.

Just my dos centavos, also from an engineer, for whatever that's worth.

 

On https://www.aircraftspruce.com/search/search.php?s=fuel drain valve  Notice that most drain valves have the drain holes at the top of the thread. Why so many other planes opted for them? 

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5 minutes ago, Gagarin said:

On https://www.aircraftspruce.com/search/search.php?s=fuel drain valve  Notice that most drain valves have the drain holes at the top of the thread. Why so many other planes opted for them? 

If it's engineered for it so that it fits the tank shape and desired drainage, it's the appropriate thing to use.    If the threads of the fastener extend below the tank rather than into it, it'd be an obvious thing to use.   I can think of a lot of reasons where it would make sense, but they're not applicable to a typical Mooney tank.

 

Edited by EricJ
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Slightly off theme but related to the topic: Is it advisable to test by adding a known volume of water, say that of a half a fuel sampler cup, to the tank, let it sit overnight and then sample through the valve? Theoretically that volume of water should come out the valve if functioning as it should. 
Please forgive if it’s a stupid question, I’m not an engineer!

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Peter,

not advisable...

Even In the most recent tanks from the Mooney factory...

The drain hole is not at the lowest corner of the tank...

The low corner is square in shape, and the drain is round and mounted a few inches away...

Sooo.... when getting water in the tank... there is some that isn’t going to drain...

water usually doesn’t stay forever... as some small amount will get adsorbed over time...

there are some ways of using dry gas if this occurs... ‘dry gas’ a chemical that has affinity for both gas and water...

I think the POH may have recommendations for what can be added to the fuel...

This is good to know the first time you get fuel cap leaks while you are out in the rain...

That low point is where junk settles, and water settles... the drain is above it... and the fuel pick-up is even higher...

unfortunately... a good bumpy ride bumps everything around...

PP thoughts only, not a mechanic...

Best regards,

 -a-

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4 minutes ago, EricJ said:

If it's engineered for it so that it fits the tank shape and desired drainage, it's the appropriate thing to use.    If the threads of the fastener extend below the tank rather than into it, it'd be an obvious thing to use.   I can think of a lot of reasons where it would make sense, but they're not applicable to a Mooney tank.

 

As the tank ages there will always be small flakes of debris (sealant flakes) that do not float but that it can flow into the -53S causing it to jam/leak. This problem does not happens with valves that drain above the debris field.

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32 minutes ago, PTK said:

Slightly off theme but related to the topic: Is it advisable to test by adding a known volume of water, say that of a half a fuel sampler cup, to the tank, let it sit overnight and then sample through the valve? Theoretically that volume of water should come out the valve if functioning as it should. 
Please forgive if it’s a stupid question, I’m not an engineer!

If you add water at the fuel cap it has to run through multiple chambers, through ribs, to get to the sump drain.   It can get temporarily trapped at the ribs along the way, especially if the weep holes in the ribs are clogged up a bit.   There's been an AD to make sure those aren't clogged.   The upshot is that the water might hide behind a rib for a while and get dislodged during flight, like, say, during pitch up for takeoff, and then get ingested, which makes for possible bad timing for a power loss.   

So, yeah, not really advisable.  ;)

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7 hours ago, Gagarin said:

On https://www.aircraftspruce.com/search/search.php?s=fuel drain valve  Notice that most drain valves have the drain holes at the top of the thread. Why so many other planes opted for them? 

These valves are designed with the holes on the end because the mounting flange is on the outside of the tank, unlike yours which places the flange inside the tank. Please confirm that the flange in the picture I posted is done in accordance with your STC??

Just crawl under a Piper Cherokee, you’ll see that the flange is a machined disc riveted and sealed to the outer tank skin.  The valve, which is a pipe thread version is screwed into the flange to a height which places the holes at the bottom of the tank.  

If you look at a typical Cessna tank they welded heavy walled bushing into the bottom of the tank, this also places the drain holes at the bottom of the tank.

On many bladder tanks there is a heavy walled rubber nipple bonded on the outside of the tank at the lowest point, the drain valve is inserted into the nipple.

These engineers seem to grasp the concept of placing the drain at the lowest point in the tank.

Clarence

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