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Cork, rubber or just proseal tank gaskets??

glider4

Well Known Member
I need help! There are lot's of posts about proseal and tank leaks but I haven't found a thread about this specific subject.

OK, I'm about ready to seal the T-408 cover and fuel sender to the gas tank. I've looked at various builder web sites and see about every possible combination of using or not using the cork gasket with proseal when sealing the T408 to the tank. The only common factor I could see was liberally "prosealing" the bolt threads going into the nutplates.

Likewise, I see different approaches to sealing the fuel sender cover to the T-408.
1. Using just the rubber gasket without proseal
2. Using proseal with the rubber gasket
3. Tossing the rubber gasket and just prosealing the fuel sender "cover" to the T-408

What's the best way to do this and minimize the chance of geting a leak at the T-408 and fuel sender covers?

Al Thomas
RV-8a
N880AT (reserved)
 
I think the current trend is to use proseal and nothing else, although I would submit that with careful technique any of the methods you listed will work.

My tanks went 5 years without leaking with proseal over cork gaskets. When I pulled the access covers and senders off to complete the fuel tank service bulletin this spring, I only used proseal. No problems with that installation either.
 
I just did mine.

Thin layer of proseal on the rib, then cork, then thin layer of proseal on the cover plate. Dipped the threads and inserted the screws and tightened. A little squeezed out the edges and I formed that into a fillet.

No leaks on either tank.

I have no plans to remove them ... ever ... but we'll see how that goes :D

Thomas
 
after the leak

some of the cork on mine sqeezed out when tighting the screws but I put
proseal all over and under the cork also used special screws with o-rings on the head of the screws, (hope they work) I was wondering.. when yall did the sb did you remove the wings ? remove the tanks or did it in place.. mine looks like, no where near enough room to do anything in that tight place.. can
work be done in the gap ? or did yall remove the tanks ?


Danny..
 
Regarding Danny's method...proseal - cork - proseal...seems like there are two too many ingredients...the extra layer of cork and proseal are redundent and all three provide potential for a leak. Might as well revert to one layer of proseal and only have one possibility for a leak.
Seriously, though....I did my RV6 using the gaskets and fuel lube. This worked out pretty good for over seven years with only minor seepage when I first started flying the plane.
On the RV8, I just used proseal, with no leaks from the get go.
I prefer the proseal only method.
 
threads

the nut plate isnt sealed to the plate so sealing the threads is useless, unless what you really mean is just sealing the screw to the plate. i tossed the gaskets but they will work fine, if your gonna apply sealer to both sides of the gasket then you dont need a gasket. often times sealer will cause a gasket to squirm out of position when torquing because the sealer acts like a lubricant when wet. as fat as the rubber gaskets are the screws arent really long enough to use with the rubber gaskets. so i tossed them as well. we used the same set up on helicopters and it worked well. all proseal no gskt.
 
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In retrospect I'm not sure exactly why I used the cork in the middle ... I think if I were to do it again I would just use proseal. I'm sure it wouldn't leak either.

It might be easier to remove the plate sometime if there is a sacrificial cork gasket in there, but you're still stuck removing and cleaning all the proseal anyway...

Thomas
 
Proseal only!

Thanks for the feedback everyone. Looks like the cork and the rubber gaskets will get tossed. By-the-way, I have a QB wing so the tanks were pretty much completed on delivery. And they did liberally proseal the nut plates on the tank side where the T-408 bolts go in. The only thing not prosealed on these nut plates is the tip where the bolt will stick out. Doing the SB was easy with no proseal to clean out first - I got off easy on that one.

Al Thomas
RV-8a
N880AT (reserved)
 
glider4 said:
Likewise, I see different approaches to sealing the fuel sender cover to the T-408.
1. Using just the rubber gasket without proseal
2. Using proseal with the rubber gasket
3. Tossing the rubber gasket and just prosealing the fuel sender "cover" to the T-408

What's the best way to do this and minimize the chance of geting a leak at the T-408 and fuel sender covers?

The best way to prevent leaks is probably to use proseal. However, I didn't like the idea of having to remove that stuff if I ever had to service these units. And I did have to service them.

I just pulled my fuel senders to troubleshoot the reasons for unreliable gauge readings. When first installing them, I just used the supplied rubber gasket and attached them with the stainless pan head screws that have the integral o-ring (from McMaster-Carr). During two condition inspections I didn't see any leaks. However, when I removed the root fairings this time, I did see that the left sender was weeping a little. It was hard to tell where it was coming from, but I suspect it was from under the screws. I didn't know any better when I first installed them and just used the suppled o-rings, which are silicone rubber. I found that the screws were not very tight. Maybe the o-rings had started to deteriorate. Anyway, I had already determined that I needed to replace the o-rings with viton ones. This has been suggested here and other places many times. However, I haven't seen anyone report on where to find the correct size o-rings. The silicone model that the screws come with is a very unusual size---about .047" thick. I couldn't find any comparable o-rings anywhere. Another local RV builder said he found a source but they were a custom size and cost about $1.50 each. Yikes! No way I was doing that. I decided to try the closest size I could find, which was a nominal 1.5 mm x 4 mm ID model from McMaster. That's a little thicker than the original (it measures about .058") but the ID is perfect and they seem to work fine. I ordered new rubber gaskets from Van's and reinstalled the senders with no leaks so far. We'll see how these hold up in service.

In case you're interested, the part number for the self-sealing screw is 90825A819 and the viton o-ring is 9263K289.
 
Ptoseal and cap screws

There were many past posts concerning gaskets and fuel lube
with fuel leaks. I used proseal only and stainless allen head
cap screws with a proseal bead under the head. No leaks in
750 hours.

George Meketa
RV8
 
Being totally ignorant ...

I thought the cork gaskets supplied by Van's were the proper way to seal the tank access covers. Disaster! The day after calibrating the senders I had a major fuel spill inside the airplane and all over the hangar floor. With tip tanks I had a lake in the general shape of an an airplane without a horizontal stabilizer. Thinking that the cork would provide a sacrificial separation point for maintenance I removed the tanks, cleaned everything up and added proseal to thew process. Still had seeping leaks around the screws. Cleaned this area and added proseal over the screw heads and every thing seems OK after approx. 270 hours of operation but this is one area of my work on the plane that I wish I had to do over with fresh tanks. The cork would be thrown away and I would only use proseal at every joint, penetration and interface.

Bob Axsom
 
Proseal ONLY! Van's Float Seal Bending Diagram specifically says to discard the rubber gasket supplied with the sender. I just replaced my 11 year old senders, and I was shocked to find the builder only used the rubber gasket. It was not leaking, but the gasket fell apart as I removed the sender. It was cracked throughout. Just a matter of time before I had big problems. The only good part is the senders came out easily and prep for the proseal was a piece of cake (no sealant to clean up!).
 
I am sure proseal works well. I didn't have any laying around and made a gasket from felpro gasket material. The stuff engine gaskets are made from. I used an anaerobic sealant on both sides of the gaskets and on the screws (head and upper thread area). No leaks in 5 years and don't expect any problems down the road.

Larry
 
We just opened up the on-wing tanks on our club RV9A prompted by weeping from both covers. Cork + unidentified sealant.

Cleaned off all the old stuff on both sides with a Scotch Brite wheel and Dremel scourer wheel, followed by wax & grease remover then contact cleaner. Access was fun but definitely doable.

Masked up 5mm beyond the circumference on the airframe side and gooped the interfay with a 2mm thick layer on both sides using 1422 B2. Fasteners were installed wet although it wasn't necessary with all the excess oozing into the holes. Fasteners were sealed around the heads as well. Tightened them only enough to ensure there was slight bead forming around the perimeter of the cover and at least a 1mm layer of sealant would remain for the interfay. It was guesswork. Let that sit for a week before filling the tanks.

We've had some bloody warm days on the west side of Australia prompting full tanks filled in the morning to spit fuel out the vents in the middle of the day. That was a welcome leak.

Feels good to know that the buggars are sealed up properly and won't be sending fumes into the cockpit ever again.
 
And a few months on and these tanks have remained completely leak free (where we have sealed).

I'm reposting because we had to go back into the left tank to resolve a leaking BNC connector from the fuel capacitance system, installed prior to our taking ownership.

The tank access cover was removed with great difficulty and revealed a uniform interfay seal between cover and tank rib of about 0.5mm. There was also a consistent bead of sealant around the circumference of the tank rib hole and the outside perimeter of the cover plate.

Coming from the airline world where proseal and AVTUR is the norm, I'm glad to see the results with AVGAS, and our tank is once again sealed tight.

Just have to remember to let it cure fully before chucking fuel in. 30 hours in our case. Very important point.
 
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An alternative

I have a different process that has always given great results, and has the added advantage that it is pretty easy to re-open and clean up, then re-seal if needed.

I use the cork (or rubber) gasket, coated on both sides with one of two very similar products. One is called Permatex Hi-tac, the other it Permatex Aviation Form-a-gasket. Both of these products are a chocolate brown syrup that coats and impregnates the gasket, the screws and threads. Both are very resistant to fuels.

I have always done this on my cars. I have done this on two RV wingsets. No leaks. I have had to open one tank up to replace a fuel level sender. Easy. then clean up with solvent (acetone and MEK, I think) and re-seal.

Another pro tip -- use allen-head cap screws to hold the tank plates on. That way the screws can be easily removed with the wings on the fuselage, working in the narrow space.
 
We got our QB kit delivered a few weeks ago, and I saw the cork gasket on the drawing, but it wasn't listed in inventory and definitely didn't get delivered. The instructions still mention it too, but I figured a little proseal would be just fine.
 
Timely thread! Josh's RV-9A had quite the fuel leak. I pulled off the wing root fairings and found the gasket under the fuel sender leaking like crazy.

IMG_8493_heic-M.jpg


Proseal is ordered and on the way from Van's. I got some new, much thinner, Viton gaskets from Aircraft Spruce, but now I'm not sure whether to use them in addition to the proseal.
I looked at what I did on my RV and I did use proseal in addition to the gaskets.

The sender came out easily with the wing root fairing taken off.

IMG_8494_heic-M.jpg


No sign of any proseal on the sender except for some under the screw heads.

IMG_8495_heic-M.jpg
 
I really like the idea of Allen key bolts!

Would have fitted those had they been available here in Western Australia. Takes too long to ride a Kangaroo to the eastern states where the bounty is plentiful.

The stuff that our fuel sensor was coated in was a tar-like substance that could be scrapped off with a fingernail. When AVGAS permeated through it became yellow and smelt like diesel. Does that sound familiar to anyone?
 
Pro Seal Only

I used Pro Seal only with allen head screws in case I ever have to remove from the gap. But to be honest if there is ever a problem it will be easier to remove the tank from the wing. Did that once to fix a rivet weep with green Loctite many years ago. So far all good after 11 years of flight.
 
After having my leaking QB tanks finally repaired, the dog gone fuel sender center screw rotates the inner thru-piece when I try to tighten it. Fortunately I have a new sending unit for that tank so now I *only* have to get the pro seal removed. Are others having trouble with the sending units like that? Both of my sending units rotated the thru-piece.

-Marc
 
On both my RV-4 and RV-7 I used the supplied cork gasket with Aviation Form A Gasket. Cap screws with washers just snugged up. No leaks ever!!
 
Not sure if there is an answer to this question but in my 40+ years of owning and operating automobiles not once have I had a fuel tank leak from a sending unit. Rivets I can see but why the all the grief with these fuel tank senders? Is avgas that much harder to contain than diesel or gasoline?

Keith
 
Not sure if there is an answer to this question but in my 40+ years of owning and operating automobiles not once have I had a fuel tank leak from a sending unit. Rivets I can see but why the all the grief with these fuel tank senders? Is avgas that much harder to contain than diesel or gasoline?
Keith

Sending units are typically mounted on the top of automobile fuel tanks where they are seldom, if ever, continuously below the level of fuel.
 
Gravity and variable head pressure and repeated prolonged exposure? Aren't sender cover plates usually on top in boats and autos and are on the side in RV aircraft?
 
I try to forget the number of times I've had the tanks off to fix leaks in the access panel, the sender, a BNC connector, and a few rib rivets on my 15yo RV9A.
I've used cork a couple of times.. leaked.
I've used regular Proseal only - don't remember if it leaked, but getting the access panel off was one the the most difficult things I've had to do.
After that, I used "removable" Pink proseal and haven't seen a leak in at least a few years.

See https://vansairforce.net/community/showthread.php?t=8835
and https://vansairforce.net/community/showthread.php?t=38564
 
I used the "access panel" sealant and cork "dots" (punched out of the cork gasket) on each side of the screw holes to establish a uniform sealant thickness when the screws are snugged down. That way the sealant is not squeezed out around the screws, and should make it easier to cut the plate off with safety wire or similar if the need ever arises.

The old proseal-only job on my 6's tank access plates is holding up (20 years on), but one rubber sender gasket failed a couple years ago. I'm dreading a repeat on the flop tube tank, as that will require a tank pull.
 
I used the "access panel" sealant and cork "dots" (punched out of the cork gasket) on each side of the screw holes to establish a uniform sealant thickness when the screws are snugged down. That way the sealant is not squeezed out around the screws, and should make it easier to cut the plate off with safety wire or similar if the need ever arises.

The old proseal-only job on my 6's tank access plates is holding up (20 years on), but one rubber sender gasket failed a couple years ago. I'm dreading a repeat on the flop tube tank, as that will require a tank pull.

I have used proseal for the big access panel and the rubber gasket for the smaller fuel gauge one. The reason that I prefer to use the gasket, the chance of the fuel gauge unit to need maintenance is more and would make replacing it a much easier job. Otherwise, great chances are that you would need to pull the tank just to replace that.
Also, the rubber gasket holds pretty well, neither of my planes leaked using that.
 
Curious, why no one uses NAS 1473 series sealed nutplates instead of open nutplates. I did and when combined with a simple gasket around the flange of the access panel and the sender, no leaks in 23 years. No proseal mess to deal with.
 
Curious, why no one uses NAS 1473 series sealed nutplates instead of open nutplates. I did and when combined with a simple gasket around the flange of the access panel and the sender, no leaks in 23 years. No proseal mess to deal with.

I did.

I have used proseal for the big access panel and the rubber gasket for the smaller fuel gauge one. The reason that I prefer to use the gasket, the chance of the fuel gauge unit to need maintenance is more and would make replacing it a much easier job. Otherwise, great chances are that you would need to pull the tank just to replace that.
Also, the rubber gasket holds pretty well, neither of my planes leaked using that.

Actually, you can remove the sender (non-flopper tank) without pulling the tank. Not as hard as you might imagine. You'll get to try it in ten years or so! :D
 
I did.
Actually, you can remove the sender (non-flopper tank) without pulling the tank. Not as hard as you might imagine.

Bull. I'm trying to remove my sender right now. It was pro-sealed in. I got the screws out but how the heck do you get the sender loose? Mine is stuck good and tight.

-Marc
 
Bull. I'm trying to remove my sender right now. It was pro-sealed in. I got the screws out but how the heck do you get the sender loose? Mine is stuck good and tight.

-Marc

Take a piece of 1 X 1/8" steel and put a 90* bend on it. Levave the long part about a foot (or whatever fits into the wing root gap) and the small part about an inch. Then grind a 1/2" long bevel on the short part (flat on outside, bevel on the inside. Use a small hammer to tap the sharp end of the bevel into the sender / tank gap, where the proseal is. I would probably just tap a razor blade in there, but what I mention above is safer. A heat gun will also help to soften it up as well.

I used a custom made gasket with anaerobic sealant to specifically avoid the issue you are having.

Larry
 
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Take a piece of 1 X 1/8" steel and put a 90* bend on it. Levave the long part about a foot (or whatever fits into the wing root gap) and the small part about an inch. Then grind a 1/2" long bevel on the short part (flat on outside, bevel on the inside. Use a small hammer to tap the sharp end of the bevel into the sender / tank gap, where the proseal is. I would probably just tap a razor blade in there, but what I mention above is safer. A heat gun will also help to soften it up as well.

I used a custom made gasket with anaerobic sealant to specifically avoid the issue you are having.

Larry

Thanks Larry. I tried a brand new flexible putty knife that had a 45* bevel ground on the end of the blade and the pro seal laughed. Maybe heat but I'll purge the tank with nitrogen first and sharpen the putty knife to be thinner and with a longer bevel.

Marc
 
i used cork gasgets and the standard rubber thingy with nothing else and it doesn't leak so far. but the tanks were fueled first time a year ago and likely it will leak someday.

don't want to use proseal. i ran out of it and it's very expensive here (seems for us europeans they mix gold into it). and it would be my luck that after prosealing the parts the level sender has to be serviced a week later.

i really like the idea of using Permatex #2, to smear it on both sides of the cork/rubber gasgets. permatex is available and i have good experiences with it. is anybody concerned that parts of the permatex go into the fuel and will cause problems?
 
Permatex #2 shouldn't dissolve in avgas. But a better gasket sealant, and what I use, is Hylomar Blue. If you don't have a tube of that, or if you every use fuel with ethanol, then I recommend using Permatex Fuel Sealant, which will do the job well and doesn't break down in ethanol either.

Note that Permatex #2 is cleaned up with alcohol, which ethanol is, but Fuel Sealant takes either toluene or MEK to clean up.

I've used Hylomar for many years, mostly with industrial high pressure fluid systems, but it works very well, yet can be removed and cleaned up fairly easily.
 
Curious, why no one uses NAS 1473 series sealed nutplates instead of open nutplates. I did and when combined with a simple gasket around the flange of the access panel and the sender, no leaks in 23 years. No proseal mess to deal with.


So my question to the experts is:
I have QB wings on order for my 10. If I want to add the NAS 1473 nutplates to the fuel sender openings can I do this when I receive the wings? Will the existing nutplates be easy to remove and the new ones installed? Is there adequate access?
If it’s doable what size of screw is used 8/32 or 10/32?

Thanks
Keith
 
I did.



Actually, you can remove the sender (non-flopper tank) without pulling the tank. Not as hard as you might imagine. You'll get to try it in ten years or so! :D
I agree that it can be done and I believe it is easier with the gasket then proseal as cleaning the proseal with the tank in place will be a pain.
 
I agree that it can be done and I believe it is easier with the gasket then proseal as cleaning the proseal with the tank in place will be a pain.

And I believe that the model RV will make a difference in how difficult (or easy) it is to access the sending unit. It appears that some RV's have move room than others.

-Marc
 
So my question to the experts is:
I have QB wings on order for my 10. If I want to add the NAS 1473 nutplates to the fuel sender openings can I do this when I receive the wings? Will the existing nutplates be easy to remove and the new ones installed? Is there adequate access?
If it’s doable what size of screw is used 8/32 or 10/32?

Thanks
Keith

Yes, it would be fairly straightforward to make this switch. I think they are 8-32, but don't trust me, check the plans.
 
So my question to the experts is:
I have QB wings on order for my 10. If I want to add the NAS 1473 nutplates to the fuel sender openings can I do this when I receive the wings? Will the existing nutplates be easy to remove and the new ones installed? Is there adequate access?
If it’s doable what size of screw is used 8/32 or 10/32?

Thanks
Keith

I used NAS 1473 on my tanks. Typical engineer, always trying to improve "good enough". As usual, the law of unintended consequences kicked in. Been a while since I built my tanks, but I seem to recall the NAS 1473 caused an interference with the fuel pickup tubes (with the screens, not the sawcut type) and I had to re-make them.
 
Thanks Larry. I tried a brand new flexible putty knife that had a 45* bevel ground on the end of the blade and the pro seal laughed. Maybe heat but I'll purge the tank with nitrogen first and sharpen the putty knife to be thinner and with a longer bevel.

Marc

I finally got the %$@#$ pro-sealed sending unit out last night. I ended up grinding the thickness (of the brand new putty knife I bought) down to something thinner and more flexible. Once I got the knife started I had the sender out in a couple of minutes. There was no gasket, only pro-seal.

I'll put the new sender in with the rubber gasket and Aviation Permatex. BTW I got the Aviation Permatex from O'Reillys auto parts! Who knew?

-Marc
 
I finally got the %$@#$ pro-sealed sending unit out last night. I ended up grinding the thickness (of the brand new putty knife I bought) down to something thinner and more flexible. Once I got the knife started I had the sender out in a couple of minutes. There was no gasket, only pro-seal.

I'll put the new sender in with the rubber gasket and Aviation Permatex. BTW I got the Aviation Permatex from O'Reillys auto parts! Who knew?

-Marc

I would re-think rubber. That will shrink and ultimately crack and the sealant won't help. Scott and I used a more stable gasket material that will absorb the sealant and therefore works well because it is dimensionally stable over time. Rubber is not. That same sealant on rubber won't help once the solvents release and it shrinks and cracks. This is not a good application for a rubber gasket IMHO.

Larry
 
I would re-think rubber. That will shrink and ultimately crack and the sealant won't help. Scott and I used a more stable gasket material that will absorb the sealant and therefore works well because it is dimensionally stable over time. Rubber is not. That same sealant on rubber won't help once the solvents release and it shrinks and cracks. This is not a good application for a rubber gasket IMHO.

Larry

Thanks Larry, but I'm gonna give it a try. Steve Smith used that method and says it has lasted 11 years so far. If it does leak it's easy to R&R the sender and reseal.

People with a higher pay-grade than me designed the rubber gasket method so I have to believe that it's gonna last a while. If I get 10 years out of it then I'm golden!

-Marc
 
Thanks Larry, but I'm gonna give it a try. Steve Smith used that method and says it has lasted 11 years so far. If it does leak it's easy to R&R the sender and reseal.

People with a higher pay-grade than me designed the rubber gasket method so I have to believe that it's gonna last a while. If I get 10 years out of it then I'm golden!

-Marc

Good luck. Must have mis-read. Thought steve said he used cork, which is stable and doesn't shrink or crack over time, though has porosity issues that can be addressed with sealant. Can't speak to the designers, but have seen numerous posts where buiders used the rubber gasket and it starting leaking in less than 10 years. As mentioned Sterwart Warner designed that gasket back in the 60's or 70's when every fuel tank has it's sender mounted on top of the tank and didn't see continuous fuel exposure. Also a time when vehicle warranites were one year and the cars life expetancy was well under 10 years. My BMW has rubber valve cover gaskets and they start leaking religiously at 6-7 years after installation. It's typical for buna-N rubber to shrink and become hard over time.
 
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Thanks Larry, but I'm gonna give it a try. Steve Smith used that method and says it has lasted 11 years so far. If it does leak it's easy to R&R the sender and reseal.

People with a higher pay-grade than me designed the rubber gasket method so I have to believe that it's gonna last a while. If I get 10 years out of it then I'm golden!

-Marc

With all due respect to Steve (and he deserves a LOT of respect), the exception doesn’t usually prove the rule, and every (else) that I know that has used the rubber gasket for the fuel sender has had it swell, get slimy, and leak. Remembrance that the fuel senders are not made for aircraft use, and therefore there is no assurance that what the gasket was made out of 15 years ago is still what they make it out of today.

I have even them leak after a year of continuous fuel immersion....

Paul
 
never again

I am solidly in the camp of NO gaskets of any kind. Had rubber swell, squeeze out, go to ^@^ in a hand basket. Cork weep and all the other problems. Been there done that. Proseal only. If it will seal the gazillion rivets why not use it to seal the ends.
Never had any problems removing end plates. Drain the tanks, Pull them if you can. Heat gun very thin putty knife and off they come. Removing the tanks ain't no big deal either unless you've painted the screws in.
I'm getting to old to not like easy.
Problem solved Art
 
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