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Dripping Fuel Tank Drain

L

lr172

Well Known Member
I am just out of Phase I and I am getting dripping from one of my fuel drain fittings. Seems whenever I drain some fuel, I need to do a bunch of fiddling with the drain to get it to stop dripping. I bought a new drain, as well as replacement seals/o-rings. Is this likely a defective drain or should I start with replacing the seal? Also, could this be caused by debris? I can see VERY small elements swirling in the tester cup. However, they don't seem large enough to create a problem with the seal.

Larry
 
Larry,

My experience with those is that if it is leaking you probably have some foreign matter lodged in there....replace it with the new one you got and inspect the old one to see what is stuck in the valve. It sounds as though the original one is fairly new, so I doubt you have a seal issue.
 
lr172 said:
I am just out of Phase I and I am getting dripping from one of my fuel drain fittings. Seems whenever I drain some fuel, I need to do a bunch of fiddling with the drain to get it to stop dripping. I bought a new drain, as well as replacement seals/o-rings. Is this likely a defective drain or should I start with replacing the seal? Also, could this be caused by debris? I can see VERY small elements swirling in the tester cup. However, they don't seem large enough to create a problem with the seal.

Larry
Click to expand...

Larry, yes more than likely you have an aluminum chip or some other debris hanging up on the O-ring. What I have done with some success is remove the fuel drain, let a small amount of fuel drain into a bucket, and then re-install the drain. I keep a spare drain just for this purpose. I take the spare, put a new o-ring on it, put some thread sealant on it, and swap it out with the one that's dripping. The old one now becomes your spare. It makes just a little mess and some fuel will run down your arm, but not a big deal.

Now look in the bucket, you'll probably find your chip or other bad stuff. And everyone should know this, but don't use RTV! Permatex #2 is a good thread sealant. I never miss an opportunity to warn folks against RTV in their fuel system--anywhere!
 
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Not uncommon

There isn't much to these little drains, and I have seen many leakers. I keep spare ones in my shop. I have had mine leak on my -4, as it only takes the smallest bit of debris to cause a leak. When I sump, I typically grab it and rotate it back and forth. If you think your tank is "dirty", it wouldn't hurt to do a drain/flush on it.
 
Usually gets better with time. I keep a spare in my tool kit. Not to hard to change even with a full tank if you're quick and have everything at hand. John
 
Thanks for the help here. I had been thinking debris was the likely culprit but good to hear that confirmed by others. I will pull it, drain a bit and replace with the new one.

Thanks,

Larry
 
Larry, coat the o-ring with a little bit of fuel lube. It will help it to stay lubricated and maintain a good seal.

:) CJ
 
Pat Hatch said:
I take the spare, put a new o-ring on it, put some thread sealant on it, and swap it out with the one that's dripping. The old one now becomes your spare. It makes just a little mess and some fuel will run down your arm, but not a big deal.
Click to expand...

A small tip...if you approach the fuel drain while standing at the leading edge instead of from beneath the wing you won't have fuel running down your arm during the swap. A pair of disposable gloves will prevent any exposure to fuel.
 
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Sam Buchanan said:
A small tip...if you approach the fuel drain while standing at the leading edge instead of from beneath the wing you won't have fuel running down your arm during the swap. A pair of disposable gloves will prevent any exposure to fuel.
Click to expand...
Also, you can eliminate fuel running down your arm by having your wife put her finger on the hole while you swap the drain. :D
 
Debris are the major cause. Some are foreign objects drawn with fuel as shown in the picture below but some could be self inflicted. Once on a long trip I tried to "work" a dripping drain. It stopped but at next fuel stop when activated it was pouring and impossible to contain. I run for a wrench and a plug. Unscrewed the drain and found two O-rings sliced out of one. I was pulling drain so aggressively it circumsized itself :D


 
A local A&P put compressed air through the drain, 25psi or so. Obviously the tank cap was off. He said he'd done it many times with many different aircraft.

After a small blast of air, a tiny amount of debris was drained from the tank, and the drain never leaked again.

I cannot vouch for the wisdom of this method (although I am curious what everyone thinks)... but it can and did work.

-jon
 
"Ground" your aircraft

All good advise but I would add one more piece of advice when messing with
fuel drains.
"ground" your airframe, especially if you are replacing the drains with fuel in the tank and inside a hangar.
BTW, I do exactly the same as others, always have a spare with a new o-ring
and replace the leaky one with a new one but I attach a ground cable from the hangar to the airframe.
 
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