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  #1  
Old 12-05-2015, 07:54 AM
paul330 paul330 is offline
 
Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
Default Fuel Leak

After my last flight, there was blue staining on both sides at the wing root and down the gear legs. Not a huge amount, but obviously needs fixing. Had the root panels off - no signs of leak. So seats out and tunnel panels off. Sure enough, the leak seems to originate in the tunnel and flowed out across to the wing root.

I should mention now that my fuel system is modified a little. UK regs require a gascolator but with the wing fuel drains being at the low point, it's a bit redundant. A mod has been approved to remove the inline filter and put the gascolator in the tunnel to act as a fuel filter only. Using the Andair version means easy cleaning by screwing off the bowl. I also use the Andair fuel selector. All piping is standard flared aluminium fittings.

Witness stains in the tunnel indicate that the leak is from the mid-section. This is good news as if it was forward by the pump or red-cube it would be a real PITA. I know that red-cubes have been a potential source of leaks but this does not appear to be the case.

Now here's the problem - I can't find the leak. This is bad news as a tunnel leak is potentially very serious. I initially just tried the fuel valve left/right to see if anything leaked. Then I tried again with the booster pump on. Nothing..... From what I can see, the leak has to be from the selector, gascolator or maybe the inlet to the fuel pump.

Could it be that the tunnel flexing in flight is causing a joint to weep? In which case it is going to be extremely difficult to track down. I think my next step is to take her out for a high power engine run and see if I can spot any drips. Obviously, though, I did that during the initial ground tests and all was well. Other than that, I could try tightening the joints but I don't want to end up over doing it. I could take them apart, check the flares and threads, clean and re-assemble but access is a bit tight with the panel and controls in place and I don't want to make things worse.

Any advice appreciated......
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Last edited by paul330 : 12-05-2015 at 07:58 AM. Reason: typo
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  #2  
Old 12-05-2015, 08:35 AM
Bill.Peyton's Avatar
Bill.Peyton Bill.Peyton is offline
 
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Location: St. Louis, MO
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Default

I initially had fuel leaking in the wing root around the fuel level sending units. I had used the neoprene seals provided with the sender. I changed them out to cork with a little Permatex gasket sealer and the issue is gone now for 500 hours.

Look closely around the bolts that hold the sending unit to the tank.

How about your tank vents, are they protruding enough into the air stream or could vented fuel be running back into the wing root cover?

I can't imagine there would be enough flex in the lines to produce leaking in the joints. I would inspect each joint for cracking in the flare if possible.
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  #3  
Old 12-05-2015, 08:53 AM
Pat Stewart Pat Stewart is offline
 
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Location: Granbury Texas
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The first thing I would is to check all connections and see if any are loose. If not I would start disconecting each connection looking for bad or cracked flares. Access is a pain. On my ten I built in an access panel on the co pilot side but I also had a center console.
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  #4  
Old 12-05-2015, 09:08 AM
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Carl Froehlich Carl Froehlich is online now
 
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If you have a drain valve on the gascolator, I would suspect this first. Considering the locations, I don't see how a drain valve would be of any use.

Next would be the gascolator 'O' ring. As a cut ring is hard to see, just go ahead and replace it.

After the above two suspects, I'd guess you have a fuel line fitting problem. Assuming you already looked for a loose fitting, tightening of already tight fittings will not help. Under no circumstances should you attempt to "seal" the leak with RTV or other such stuff. The flex issue you describe is something to design around.

This leaves the fix as biting the bullet and remake the aluminum fuel lines and fittings, giving close attention to properly making the flared ends. If you are not using the right tool (like this; http://www.aircraftspruce.com/catalo...?clickkey=4577 ) you will not be successful. Pay attention to how much you are "pulling the fitting together" when you tighten the flare nuts. This is a tight area and you can easily deform the fit and create a lead. For the flexing issue, avoid straight runs between hard mounted objects.

Carl
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  #5  
Old 12-05-2015, 09:45 AM
paul330 paul330 is offline
 
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Location: Mpumalanga, South Africa
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Default

Leak is definitely in the tunnel, not the roots. No drain plug on the gascolator.

Guess my job tomorrow is to start disconnecting pipes and inspecting - but how can a leak be intermittent? I pressurize to 25psi with the electric pump and nada.....
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  #6  
Old 12-05-2015, 11:35 AM
jchang10 jchang10 is offline
 
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I read about this somewhere. Wrap suspects areas with aluminum foil. Leaks will show up underneath. I havent had opportunity to actually try this method yet.
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  #7  
Old 12-05-2015, 11:42 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by jchang10 View Post
I read about this somewhere. Wrap suspects areas with aluminum foil. Leaks will show up underneath. I havent had opportunity to actually try this method yet.
Even better is wrapping with white Kleenex. Even a very small amount of blue dye will be very obvious
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  #8  
Old 12-06-2015, 12:00 AM
paul330 paul330 is offline
 
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Thanks everyone. Off to the hangar today. I'll try the tissue tip before I tear anything else apart!

Or I could just leave it. Doesn't seem to be leaking now - I mean, what's the worst that could happen?
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Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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  #9  
Old 12-06-2015, 06:42 AM
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Walt Walt is online now
 
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Quote:
Originally Posted by paul330 View Post
Thanks everyone. Off to the hangar today. I'll try the tissue tip before I tear anything else apart!

Or I could just leave it. Doesn't seem to be leaking now - I mean, what's the worst that could happen?
I think we already lost one RV due to a fuel leak in the tunnel area, I would seriously recommend you find it and fix it before you fly.
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  #10  
Old 12-06-2015, 09:01 AM
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Bill.Peyton Bill.Peyton is offline
 
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Paul,
One additional thing to check. I assume you are using the Andair selector...
The input ports for the selector are held in place with 4 #4 screws. These screws should be peened in place after you have selected the orientation required for your particular installation. If these screws were not peened and have loosened up you may be leaking fuel around the connection to the selector body around the O-ring on the outlet port.
With the amount of fuel you have observed, you may not yet see any staining on the metal as it may be "washing" it clean.
Just a thought.....
Bill
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