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Fuel sensor flange gaskets

alcladrv

Well Known Member
Like many others, my -7A developed a fuel odor upon opening the canopy. I traced it back to leaking flange gaskets on the fuel sensor, which I've attached a photo of. They look to be made of rubber and are about 1/8" thick.

They are the OEM gaskets installed in 2005 when I completed the plane. That's a pretty long service life of 16 years. Truth be told, I've had fuel streaking under each wing for the past 5 years or so that I attributed to leaking quick drains, but no fuel odor in the cabin until now. I searched the forums and found many suggestions to use "ProSeal", technically ChemSeal, instead of the gaskets.

I looked on vansaircraft website for the gaskets and couldn't find them right away and with uncertain shipping delivery times, I wasn't confident ordering from them with the time crunch I had. Since I'm much closer to Aircraft Spruce East, I ordered the ChemSeal 3.5 oz all in one tube. I defueled the plane, let it sit empty for a couple of days while I waited to receive the ChemSeal, mixed up the ChemSeal, replaced the #8 screws with #8 socket head screws as some suggested, placed a bead of sealant on the inside of the screws and the screws themselves, tightened them all down on both tanks, let them cure for 3 days (primarily because it was cooler than the recommended 77F degree curing temperature), fueled the plane back up yesterday, and, viola, no leaks. So, all told, about a 10 day downtime.

BUT, and this is the whole point of this post, was it really necessary to use ChemSeal? No, not with some fore knowledge and a little advance planning. The gaskets didn't leak for 7 to 10 years. Nothing lasts forever and if you consider the gaskets a life-limited item and just replace them every 5 to 7 years, you get the same, no leaks, result. The benefit is that the flanges were very easy to remove with just a stubby Phillips screwdriver. Should it be necessary to replace a defective fuel sensor, one could easily accomplish that in a 1/2 hour after the fuel tank was defueled.

I cringe at the possibility of removing a "ProSealed" flange with the fuel tank on the plane. The socket head screws weren't really necessary, either. The 3-1/2 oz. size of ChemSeal was far more than I needed for the plane, although I had enough leftover to seal up holes in a pair of shoes that ShoeGoo didn't fix, sealed some wires on a couple of ebike controllers, repaired a frying pan for the wife, and fixed a broken light socket.

So, take your pick, the gasket or the "ProSeal" both work, but with their own caveats. YMMV
 

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Fuel sender flange gaskets

I've never been a huge fan of using straight nut plates to secure the fuel tank access cover or the fuel sender unit to it. I have found that using self sealed nut plates from B&B Aircraft Supply in Kansas (about a buck apiece) and using Proseal 1422B does a much better job in sealing the fuel inside the tank. 1422B comes in the consistency of molasses and easily covers the self sealing nut plates for added protection.DSCN1055.JPG

DSCN1049.JPG
Chuck Brietigam
RV-6XXL
 
21 years, 1600+ hours on pro-sealed plates and senders (and of course tanks), no leaks. Just one data point.

During that time I had one failed sender, took a few hours to remove / replace including getting the tank off and on. The trick there is to use a sharpened 1" putty knife.

I really like having spare proseal around as it works better by far than any other product where a flexible adhesive or sealant is needed. For example, securing velcro to sidewalls for seats / side panels etc.
 
McFarlane Aviation makes fuel quantity transmitter gaskets and screw seal assemblies for some Piper and some Cessna aircraft. the elastomer used in both is Dupont Viton. It won't curl up and distort like the gaskets in the photos did. Another point is that there is no real shelf life for Viton. I should point out that the screw seal assemblies are 10-32 thread not 8-32. For a permanent yet easily removed gasket system it is worth a look. I'm sure thousands of these gaskets and screw/seal assemblies are out there flying around and have been for a long time.
 
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