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Green Loctite fuel leak question

KiloWhiskey1

Well Known Member
My RV-10 has one weeping rivet on each tank. The offending rivets are one rib in on the top of the tanks near the forward edge of the wing-walk.

I have used two rounds of loctite 290 and think the leaks are very close to being sealed. I would like to put a vacuum on the tanks to see if I can draw any more loctite into the leaking areas.

My question is: what do I use to draw the vacuum? Harbor Freight has a $15 AC vacuum pump. Will those do the job or do I need something different altogether?

Thanks!
 
Interested to hear what people say about this.

I imagined the loctite 290 used capillary action to wick in. My thinking is if the fuel can get out without differential pressure the loctite should go in.

A powered vacuum pump could potentially put a 15 psi negative pressure in the tank which can’t be good. Maybe a Mightyvac hand pump with a couple of inches HG.

Perhaps using the recommended accelerator primer with the 290 is worth a try.
 
Tank Vacuume

Use a vacuum cleaner! You can regulate the amount of vacuum with your hand over the filler cap area.... Works great!

My RV-10 has one weeping rivet on each tank. The offending rivets are one rib in on the top of the tanks near the forward edge of the wing-walk.

I have used two rounds of loctite 290 and think the leaks are very close to being sealed. I would like to put a vacuum on the tanks to see if I can draw any more loctite into the leaking areas.

My question is: what do I use to draw the vacuum? Harbor Freight has a $15 AC vacuum pump. Will those do the job or do I need something different altogether?

Thanks!
 
Be carefull

I would be wary about pulling fuel vapor through a vacuum cleaner with a universal motor.
 
The Harbor Freight pump or home vacuum will both work fine, just make sure to not over-do it on the suction. That can be accomplished with an adjustable leakage path of some sort as previously suggested, along with a water manometer hooked up to your vent line to quantify the amount of vacuum being applied. A simple loop of clear tubing with a small amount of water in the low end of the loop will allow you to measure the vacuum in inches of water. The vacuum shouldnt exceed several inches of water to minimize the potential for tank collapse. Measure from the high mark on one side of the loop to the low mark on the other side.
 
I emptied the tank of fuel, used 20 psi of positive pressure via a blow gun for an hour to clear fumes (outside), checked the tank with a match to see if all was good (kidding), then applied vacuum to the tank via a cleaner with a universal motor, and then green Loctite to the offending rivet in a small syringe with an O-ring around the tip to maximize effectiveness. I did not blow up, and no more leak.
 
What am I missing here . . .

Vacuum is only 15psi max and more than a couple psi will crush the tank. Why waste the time or risk an afterburner on a vacuum cleaner when a 6cc syringe will easily develop 50 psi.

As a test just tried it by sticking a 6cc syringe against a pressure gage and easily got 50 psi. Now, the other unit I tried would not seal, so do a little homework, o-ring - whatever , and use a syringe to push the sealant into the crack. The smaller diameter the more pressure. A little ingenuity could be applied.
 
Be careful with a vacuum cleaner. A friend did this with a gas tank and it made a pretty good approximation to a jet engine/flame thrower :eek:. The tank needs to be completely free of fuel and fuel vapour.
 
I am working on the same issue. The first round wasn‘t successful but even made it worse. The leaking increased. I guess it is the effect of the solvent I used to clean the leak first. I guess it removed also some of the paint that helped sealing the leak. Will try another 1-2 rounds with the Loctite.

I have a pretty solid installation for the vacuum. I used some clear tube at the fuel vent. Together with the fuel valve in the off position and the filler cap locked and taped, I was able to produce a nice vacuum using a small plastik bottle (needed about 20-30 pumps/suckings). With a T-piece I produced a water column. You want 1 inch of mercury which approximates to 13.6 inch of water column (in total).

Fabian

E0F7ABC6-DBBD-4F59-B395-020CBA3F67F5 by Fabian Hummel, on Flickr

6E6CE0A4-C476-46C0-BCD5-E996C5918B67 by Fabian Hummel, on Flickr

95019CA5-C176-4EF2-A991-8D8BD3E6F7FF by Fabian Hummel, on Flickr

75CCB841-4C4F-43B1-B19B-76D98EEBC77D by Fabian Hummel, on Flickr
 
Yup, that might work. Or, you can pull the tank and use the Vans repair kit and fix it right. It's just a better way to go. BTDT.

-Marc
 
Vacuum is only 15psi max and more than a couple psi will crush the tank. Why waste the time or risk an afterburner on a vacuum cleaner when a 6cc syringe will easily develop 50 psi.

As a test just tried it by sticking a 6cc syringe against a pressure gage and easily got 50 psi. Now, the other unit I tried would not seal, so do a little homework, o-ring - whatever , and use a syringe to push the sealant into the crack. The smaller diameter the more pressure. A little ingenuity could be applied.

The air volume in your experiment doesn't really compare to the air volume in the tanks. Maybe I am missing the physics here, but it seems that way more then 6cc's of air will need to be removed from a 20 gal gas tank to create a meaningful vacuum.

I suspect the hand pumps will take forever, for the reason above, and I also wouldn't risk using an electric vac. You can buy an A/C vac pump for around $80. The pump mechanism is fully isolated from the motor. They use AN-4 flare fittings, so easy to fab up a connection to the 1/8" NPT sump. Be careful and use a needle valve of some sort to bleed off vac, as it will suck down pretty quick and put dents in your tank skin. Would come in handy if you ever need to evacuate and recharge your AC in the cars. Mine will pull down to a few thousand microns (below .1 PSI, they use microns to measure the vacuum level).

Larry
 
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Vacuum is only 15psi max and more than a couple psi will crush the tank. Why waste the time or risk an afterburner on a vacuum cleaner when a 6cc syringe will easily develop 50 psi.

As a test just tried it by sticking a 6cc syringe against a pressure gage and easily got 50 psi. Now, the other unit I tried would not seal, so do a little homework, o-ring - whatever , and use a syringe to push the sealant into the crack. The smaller diameter the more pressure. A little ingenuity could be applied.



This depicts what Bill is referencing with the syringe.
 

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I am working on the same issue. The first round wasn‘t successful but even made it worse. The leaking increased. I guess it is the effect of the solvent I used to clean the leak first. I guess it removed also some of the paint that helped sealing the leak. Will try another 1-2 rounds with the Loctite.

I have a pretty solid installation for the vacuum. I used some clear tube at the fuel vent. Together with the fuel valve in the off position and the filler cap locked and taped, I was able to produce a nice vacuum using a small plastik bottle (needed about 20-30 pumps/suckings). With a T-piece I produced a water column. You want 1 inch of mercury which approximates to 13.6 inch of water column (in total).

Fabian

Thanks for the pictures Fabian. Very helpful.

Did you notice your tank skins sucking in at all? I was thinking of producing just enough vacuum to get the tank skins to slightly draw in and then holding that level of suction while applying the loctite. This would eliminate the need for the manometer.

Also, when squeezing the bottle for subsequent pumps, how did you maintain the vacuum?

Thanks, Keith
 
OMG, use the manometer, its very simple! You dont want your tank skins sucking in! Alternatively, try the syringe technique from the outside so you never need any vacuum.
 
Hi Keith

I would also say use the manometer/water column! Just imagine you suck a little too much! Then you would wish back 10 leaking rivets ;) I haven‘t noticed anything, but didn‘t really look for it.
I used the flexible bottle und between pumps just held the clear tube closed by bending it tightly. That worked really easy. To hold the vacuum between cleaning and application of loctite I used that flat plier as on the picture
 
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MANometer. Peculiar name, especially considering my trepidation. So I manned up and built one using Harbor Freight’s cheapest AC vacuum pump and some clear rubber hose.

I’m in the process of upgrading all my fuel lines to TS Flightlines’ teflon hoses, so my tanks are empty. This allowed me easy access to the fuel tanks’ outlet fitting and vent.

The manometer hose is attached to the vent line and the vacuum pump is attached to the tank’s outlet fitting. If you look closely, the vacuum is in progress and has pulled the water column up a few inches.
8B6EA00F-4D14-4DE2-AFBA-EDF52CABE291.jpg

The vacuum pump connects to an air compressor to generate the vacuum. I used seaming pliers between the pump and fuel tank as a vacuum regulator. Even with the hose clamped off the vacuum pump pulled the water column up slowly. With the clamp off, the water column came up to the desired level in less than 10 seconds.
C67977AA-F129-4CE5-A7AF-0AE697E1C520.jpg

This pic shows the target level of 13.6” (1” Hg)
BD7C9350-F1E9-41E7-8F0A-2224DC3B4FB7.jpg

I used 3 layers of black tape around the rivet to create a reservoir for the loctite to sit in while the vacuum did its thing.
828A6788-4A2C-4F3B-B029-9FC0B7603474.jpg

It’s hard to tell how much, if any, loctite was actually pulled into the leak. I didn’t notice anything dramatic happen. The real test will be when I top off the tanks again. I’ve read that loctite 290 dries quickly in the absence of oxygen, so I sealed the tank and taped over the rivet. I’ll give it a few days to dry while I’m waiting on my new fuel lines.

Thanks to Fabian for the pictures and to Erich for the nudge to build the manometer.

Keith
 
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I spoke with the folks that maintain our corporate jets. They said they thin some PRC and put an O ring over the leaking rivet. Then they use a rivet gun to tap the O ring and force sealant into any voids.

That is done on jets with much thicker skins than we have so I am not sure of the chance of a dent.
 
I spoke with the folks that maintain our corporate jets. They said they thin some PRC and put an O ring over the leaking rivet. Then they use a rivet gun to tap the O ring and force sealant into any voids.

That is done on jets with much thicker skins than we have so I am not sure of the chance of a dent.

That is a cool idea!!!
 
Before leaving the hangar yesterday I squirted a bead of silicone around the leaking rivets on the right tank. After drying overnight, the silicone made a good reservoir for the loctite. I hooked the vacuum pump up and let it sit for awhile. This worked better than the black tape I used on the left wing. Luckily, both my leaks were on the top of the tanks.

3729A6F2-D728-44D5-8A94-C0E83BF86B81.jpg
 
I spoke with the folks that maintain our corporate jets. They said they thin some PRC and put an O ring over the leaking rivet. Then they use a rivet gun to tap the O ring and force sealant into any voids.

That is done on jets with much thicker skins than we have so I am not sure of the chance of a dent.

I wonder if PRC is resistant to 100LL. Jet fuel is kerosene, maybe similar, maybe not?
 
I wonder if PRC is resistant to 100LL. Jet fuel is kerosene, maybe similar, maybe not?

PRC just a brand name, it is what we seal our RV fuel tanks with, they use the same sealant that Vans sells on the jets. I asked before I resealed my leaking tank, I think it was called Flamemaster.
 
Just a quick follow up on the green loctite fix. I’ve been working on other things on the plane and today was the first time that I’ve filled the tanks since I applied the loctite two weeks ago. Happy to report that no leaks were observed. I waited around for an hour and the offending rivets were still bone dry. Fingers crossed that the loctite will continue to hold. I’ll watch before painting. I’m looking forward to getting rid of the old painted wing-walk.

47C837EF-E0B0-48A2-9B5D-2EC8EB872C7B.jpg
 
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Intex Double Quick III S Hand Pump, 14.5" , Black

Available for $10 on Amazon. One side of the pump outputs pressure, the other a vacuum.
 
I'd thought about buying a windshield repair kit on Amazon and putting green locktite in it instead of the windshield solution, but the manometer is an interesting concept. I may try a push - pull approach.
 
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