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Fuel Valve leak - is draining the tank my only option?

JFCRV12

Well Known Member
During condition inspection yesterday, my A&P/IA found a VERY VERY small fuel leak at the base of the Fuel Valve. Of course, I'll fix before it turns into a much worse leak. I know I'll need to remove the Fuel Valve to fix. Couple of questions:

  1. Do I need to drain the fuel tank or is there a way to cutoff fuel? I have 12 gallons in the tank.
  2. Is the only way to remove the fuel valve by drilling out the rivets on bottom of airplane? Or is there a way to take of fuel valve handle to release the assembly?

See pic for where the leak is. It actually looks like the builder didn't put thread seal on that side.

Thanks!
 

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Sealant should not be needed for a leak free connection.

Have you tried tightening the fitting?

Finn
 
Sealant should not be needed for a leak free connection.

Have you tried tightening the fitting?

Finn

I’m not familiar with the -12, but it looks like he’s circling a spot where the blue aluminum fitting has pipe threads into a brass fitting? In that case (pipe threads) then absolutely you need thread seal. If it’s a flare fitting, then you would be correct, no thread sealant needed on flare fittings.
 
Per Section 5 of the KAI:

Sealant is needed on pipe threads.

Sealant in not needed on flare fittings.

The valve body has pipe treads.

One side of the AN fittings has pipe threads to go into the valve body.

The side of the AN fittings that connects the fuel line is a flare fitting.

So if the leak is on the fuel line side of the fitting just tightening might work.

If the leak is from the pipe threads, I would remove the valve body by undoing the flare fittings from the fuel lines and the two rivets holding the assembly. Then on the bench remove the leaking AN fitting from the valve body, clean the valve body and AN fitting threads, reassemble with thread sealant, and reinstall.

Hope this helps, Dave
 
I’m not familiar with the -12, but it looks like he’s circling a spot where the blue aluminum fitting has pipe threads into a brass fitting? In that case (pipe threads) then absolutely you need thread seal. If it’s a flare fitting, then you would be correct, no thread sealant needed on flare fittings.

Sorry, I missed that.

Finn
 
John,
If you can get the two blind rivets removed from the side of the mounting bracket, the F-1259B Fuel valve Clip can be removed and the valve will come out if the fuel lines are disconnected.

Reinstalling with rivets will be very difficult but the rivet holes could be enlarged to #27 and the clip attached with #6 screws/nuts.

You will have to at least partially drain the tank to remove the valve. The tail of the airplane could be pushed to the floor which would allow for some fuel to be left in the tank (gets the fuel valve above the level of the fuel), but the condition inspection check list for the RV-12 specifies that the finger screen in the bottom of the tank be inspected. This does require draining the fuel tank.

If you don't already have it, I recommend that you get a complete copy of the RV-12 KAI. It is considered a required supplement to the Maint. Manual and makes it very easy to deal with details like the fuel valve.

You can purchase a digital copy from Van's on a USB stick for only $10.
 
Flare fittings

This an AN flare fitting and the seal occurs between the flare of the aluminum tube and the corresponding end of the blue fitting. No sealant or lubricant is required which is different from a pipe thread that uses various types of sealants/lubricants based on the fluid type in the line or air (ie. natural gas).

Now back to the flare fitting. Carefully check the nut to be sure it’s tight as it is a metal to metal contact that makes the seal. But be careful as it is possible to over tighten this assembly and crack the flare on the tube.

If leaking continues the assembly will need to be disassembled for a look at the fitting and the flare on the tube. Look for cracking or any irregularities in the shape and size of the flare. And yes the fuel in the tank will come flowing out if this joint is opened so empty the fuel if the joint is opened. You can drain the tank from the fitting on the bottom of the tank but I find this very messy. I disconnect the fuel line from the top of the gascolator and add a line I can feed into a gas can. I use the electric pump to fill the gas can. Because of the tank design the pump will change sound as the gas gets low and you should stop the pump. Let the gas go by the internal tank baffle and then continue pumping. This happens about three times, turn off-wait-restart, till the gas is pretty much out.

If the flare is good and the fitting looks good you might try a seal made of very thin aluminum and is placed over the fitting end (Spruce has these seals). The assembly is again put together and tightened down with no sealant.

Got a little long winded but I hope this helps.
 
Friend had the same situation. A slight bit of snugging of the fittings resolved the minute leak. We used a Crow's Foot wrench to get in there to do the snugging, bumped it twice, to get a minute amount of rotation out of it .

A few months later, on his 2015, the O ring seal to the vent on the gascolator needed changing out, again, gas fumes were getting in to the cockpit on climb out. About 180 hours on it, at the time.

When you own a RV-12... it's always something, little niggling fix its. Gotta love working on planes as much as flying them


If I get another newer RV-12... I'm going to upgrade to FADEC. That UL-260 looks tempting. Need to ask Larry Vandergriff if his AB version has been pretty reliable.
 
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Wow! Lots of answers in a short amount of time. Love this board.

Yes, I believe I need to pull to add thread seal. I'll drain tank, drill rivets, fix, and re-install. Will also inspect finger screen. Odd we missed then when going through the full checklist from the MM. Definitely not interested in cutting any corners. So more hangar and wrench time it is. Although I sure wish I would have flown off more fuel before inspection. I am NOT looking forward to draining the tank.

Finally, I do have the KAI both originals and electronic.

I will add that the inspection procedure on a 12 is WAY more work then on my previous C152 and Piper Cherokee 180...but it is MUCH cheaper to fix. Trade offs

Thanks!
 
Typically, draining a tank is not that bad. Just have a big funnel and enough fuel cans. Do not use teflon tape on fuel systems.....some of the paste type sealants are OK if you are sparing and careful (don't get any on first thread or two). No sealant needed or wanted on flared fittings...only pipe threads.
 
There are two items on this thread that I really wanted to comment on.

1. The comment about owning an RV12 and having to always do little maintenance items. I have to say that a lot of these items are as a result of original build. If you buy a used experimental then you should expect to do a very thorough post but inspection and as with anything be prepared to bring it to standard. Rv12 is no different to any other plane.

2. I’m surprised that the inspection procedure is way more work, the items in the inspection procedure are totally standard with the exception of removing the wings. All plans have access panels etc that can be time consuming to remove and inspect.
 
Draining the tank

When I've needed to drain the fuel tank I shut off the Fuel Valve, sump the gascolator dry, remove the sump valve in the bottom of the gascolator, wipe up and let dry the small amount of fuel spilled, install a pip thread-to-barbed fitting in the gascolator, push some poly tube onto the barb, turn on the fuel valve and drain into as many fuel cans as you need. It will drain faster if you run the fuel pump. Connect your battery charger to avoid extreme discharge while running the pump.

I had to reseal the pipe threads on my fuel valve. Kind of a pain but worth the effort. No more worries.

Sorry Pat, upon closer re-read I see you offered the same suggestion!

Now, if tightening the compression fitting does not fix the leak, then further to Scott’s comment...I’d recommend the OP go ahead and drain the tank, disconnect and remove the fuel valve to clean it up and re-apply thread sealant “on-the-bench”. Much easier to get a good look and quality job. Using the Loctite Sealant (was it #567?) solved my problem. Not hard to do if you don’t mind standing on your head for a bit. Again, worth the peace of mind.
2-cents.
 
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Done!

Easy peasy! Siphon gas, clear rest through gascolator. Drill out rivets, remove valve assembly.
Clean and seal threads, reinstall and rivet. Done! Not a drop off gas spilled and no leaks :)
 
If you partially drain the tank and depress the tail as suggested you can put an AN flare plug on the disconnected female flare while you work so you don’t need to keep the tail down.
 
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