Under Wing Flush Mount Fuel Drain Valves

[Ksaunders]

 The day before a flight this weekend I filled each tank of my 1982 M20J to full.  The next morning I found both flush mount under wing fuel drain valves "leaking" fuel onto my hanger floor.  One side had a "seeping" drip and the other was dripping a little more “steady”.  The puddles from the leaking valves on the hanger floor were no larger than a dinner plate but still enough to give me visions of total fuel loss in flight…….Pumping the fuel sampler cup several times into the drain valves eliminated the more severe and steady dripping valve but the other valve continued to have a drip of fuel develop slowly- but enough that I could wipe off an entire drip every so often during my pre-flight.  I rarely top the tanks off to full so I have not noticed this happening before.  After @ 1.5 hour flight, there was no additional dripping at the destination airport.  The plane sat all day and there was no dripping or seeping from either valve evident on the ground or on the valves before I departed to return to home base.  I’m wondering if this is somewhat normal when the tanks are filled to full or should it be cause to call in my mechanic and have the drain valves inspected/replaced?  Would appreciate any similar experiences or advice on the matter.  I have only owned the plane since August.         

[M20C]

There is a Mooney Service Bulletin on having the flush mount fuel sumps replaced.  I had one done ten years ago and the other a couple years ago when the other wing sump drain developed a leak like yours...

 

[carusoam]

A small amount of junk can make the valves not work well.

Ice can make it worse.  

They are easy enough to change out.

It may make sense to buy a new one. Exchange one, clean it, exchange the next one.  Clean the second and keep as a spare.

If you do this yourself, do it on an empty tank for safest results.  Use a torque wrench when installing.  It is easy to snap off the valve in the hole.  It does not need to be extra tight. A polymer seal keeps it from leaking, not tightness.

Best regards,

-a-

[Shadrach]

The fuel drain is the only way to empty a tank.  Even if you run it until the engine quits, you'll still have fuel at the sump...

[carusoam]

Ross,

Where have you been this weekend?  Haven't heard from you.

You know me and fuel safety....

I have watched mechanics change these out while the fuel runs out and down their arms.

I just recommend to minimize the exposure.  I have 3 gallons of unusable. 3 gals of danger is far better than 53 gallons of danger.  My POH recommends using the fuel pump to empty the tank.  Disconnect the fuel line first, of course.

Its up to the op to decide how far he wants to go.  Next, I would recommend an A&P perform the change.

it's also a good idea to allow some fuel to exit, flushing the sump.

As you know this recomendation was based on somebody unfamiliar doing the job for the first time.

You have achieved the level of guy who smokes while doing it....and debates the merits of the vapor pressure of 100ll at the same time.

Best regards,

-a-

[Shadrach]

Quote: carusoam

Ross,

Where have you been this weekend?  Haven't heard from you.

You know me and fuel safety....

I have watched mechanics change these out while the fuel runs out and down their arms.

I just recommend to minimize the exposure.  I have 3 gallons of unusable. 3 gals of danger is far better than 53 gallons of danger.  My POH recommends using the fuel pump to empty the tank.  Disconnect the fuel line first, of course.

Its up to the op to decide how far he wants to go.  Next, I would recommend an A&P perform the change.

it's also a good idea to allow some fuel to exit, flushing the sump.

As you know this recomendation was based on somebody unfamiliar doing the job for the first time.

You have achieved the level of guy who smokes while doing it....and debates the merits of the vapor pressure of 100ll at the same time.

Best regards,

-a-

[carusoam]

Ross,

I was thinking you and I covered draining fuel out of tanks before.

The rest of the sarcasm was a tip of the hat to your overall knowledge on Mooneys.

The mechanics I used to work with, literally would smoke in the hangar with open buckets of fuel in the area.  The vapor pressure of 100ll keeps it from evaporating any too fast.  Still somewhat dangerous.

Thought you were being facetious...

Best regards,

-a-

[Shadrach]

Yup, I remember it. I'd not suggest smoking around the stuff, but I too have seen some folks that are pretty cavalier with the handling of all types of fuel.  I've talked to others that think because Avgas is for airplanes, it must be ultra volitile stuff (as you know, it's not when compared to what we put in a lawn mower), and jet fuel, well that just has to be the worst...I mean it's for a JET, right? ;-)

 

I agree that it is far easier to contain 3 gal than 10, 20 etc... I was not being facetious, I pictured an unknowing pilot, wrenching off a fuel drain, about to get a shower.  Thanks for the hat tip, at first I thought you were busting my ... 

 

[flyboy0681]

Over the summer the drain valve on my left wing would not shut after taking a fuel sample, and it was coming down in a steady stream at a deserted airport away from home. This continued on for about 20 minutes as I kept poking all kinds of things in the hole until the time it finally stopped. My A&P said that very often sediment such as sand keeps the valve open and that I was lucky to dislodge it. I had him replace the unit the next day for next to nothing.

After that incident I fly with a crescent wrench large enough to remove the valve on the spot. A second person is needed to keep their finger in the hole while the other tries to remove sediment should it ever happen again.

Just something else to be made aware of folks.

[Luke]

Would anyone happen to know the part number for a replacement fuel sump drain on an M20J?  

I think it looks like a SAF-AIR SA53S, but always better to ask than guess!

[AaronDC8402]

I couldn't find anything more definitive, so I bought a pair of SA53S's for our 1989 J. I'll report back if they fit or not.

 

[Guest]

On 12/4/2011 at 3:13 PM, M20C said:

There is a Mooney Service Bulletin on having the flush mount fuel sumps replaced.  I had one done ten years ago and the other a couple years ago when the other wing sump drain developed a leak like yours...

 

 

 

The J model was born with the new style drain valves so the SB doesn’t apply.

Clarence

[Guest]

1 hour ago, AaronDC8402 said:

I couldn't find anything more definitive, so I bought a pair of SA53S's for our 1989 J. I'll report back if they fit or not.

 

That valve or an F391-53S will work.

Clarence

[buddy]

You may not think the valve is leaking but if you touch your finger on it and find your finger is damp with 100LL it’s leaking. You may not see a puddle on the floor or ramp because if it’s a slow drip it will evaporate pretty quickly and you can be sure your loosing a few gals. of fuel over a 2 week period.

Installing a new valve is no big deal, you DON’T have to drain your tanks just rap a towel around your forearm, you won’t loose any more than a quart of fuel and the towel will catch any fuel running down your arm. Do not over tighten the new valve because the nut inside your tank is riveted in place and you do not want those rivets to loosen.

[Guest]

6 hours ago, buddy said:

You may not think the valve is leaking but if you touch your finger on it and find your finger is damp with 100LL it’s leaking. You may not see a puddle on the floor or ramp because if it’s a slow drip it will evaporate pretty quickly and you can be sure your loosing a few gals. of fuel over a 2 week period.

Installing a new valve is no big deal, you DON’T have to drain your tanks just rap a towel around your forearm, you won’t loose any more than a quart of fuel and the towel will catch any fuel running down your arm. Do not over tighten the new valve because the nut inside your tank is riveted in place and you do not want those rivets to loosen.

Be very careful wrapping your arm with a towel which will then be soaked in fuel.  I’ve had an airplane fire in a hangar before, not something I wish to repeat.  

Clarence

[TimMoyer]

My 1960-M 20 C has that dripping leak as well… Still can’t figure out how to get the valve out? Looks like for rivets are holding it in… Does not look like there’s any way to screw it out… Any ideas?

[Fly Boomer]

9 minutes ago, TimMoyer said:

My 1960-M 20 C has that dripping leak as well… Still can’t figure out how to get the valve out? Looks like for rivets are holding it in… Does not look like there’s any way to screw it out… Any ideas?

Welcome to MooneySpace!  I think the earlier models were made that way.  Someone else should be along shortly with a more definitive answer.

[Echo]

1 hour ago, TimMoyer said:

My 1960-M 20 C has that dripping leak as well… Still can’t figure out how to get the valve out? Looks like for rivets are holding it in… Does not look like there’s any way to screw it out… Any ideas?

Impressive.  60+ years on a drain valve.

[PT20J]

Here's the SB. Note that the MDI F391-53S valves are no longer manufactured and are unavailable unless someone has some old stock. I found one on eBay. There is a equivalent SAF-AIR part, but it has a much stiffer spring.

SBM20-188A.pdf

[47U]

3 hours ago, TimMoyer said:

Does not look like there’s any way to screw it out… Any ideas?

Edit:  Skip is FAST today

This SB addresses replacement of the original wing tank sump drains.  

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-188A.pdf

If you have shop air available, often the debris can be blown off the o-ring and back into the tank (until the next time…).  

Edited January 20, 2023 by 47U
Credit to Skip…

[Pinecone]

11 hours ago, PT20J said:

Here's the SB. Note that the MDI F391-53S valves are no longer manufactured and are unavailable unless someone has some old stock. I found one on eBay. There is a equivalent SAF-AIR part, but it has a much stiffer spring.

SBM20-188A.pdf 208.41 kB · 3 downloads

https://skygeek.com/f3qudrva7th.html

 

[PT20J]

2 hours ago, Pinecone said:

https://skygeek.com/f3qudrva7th.html

 

But note that it is special order.  I doubt they can fill an order unless there is stock at a distributor. MDI Aerovalve is listed by Yelp as CLOSED and the phone was disconnected when I tried calling them a while back.

[N201MKTurbo]

https://www.curtissuperiorvalve.com/flush-mount-valves.html

Support the Chandler economy! Manafactured at KCHD!

[PT20J]

4 hours ago, N201MKTurbo said:

https://www.curtissuperiorvalve.com/flush-mount-valves.html

Support the Chandler economy! Manafactured at KCHD!

Good find!. I wonder if they have springs equivalent to the MDI valves? The SAF-AIR valve has a spring so stiff that it is hard to operate in the awkward position you have to be in to reach the drain. The MDI valves are crimped and not rebuidlable.

[N201MKTurbo]

1 hour ago, PT20J said:

Good find!. I wonder if they have springs equivalent to the MDI valves? The SAF-AIR valve has a spring so stiff that it is hard to operate in the awkward position you have to be in to reach the drain. The MDI valves are crimped and not rebuidlable.

I have them, they seem normal.