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Fuel System Problem #1 - The case of the dripping tank vent

Saville

Saville

Well Known Member
RV-8, 152 hours.

So this weekend I was working on my fuel sender/pressure issues when I noticed that fuel was dripping from the left hand tank vent. I was fairly certain that the outboard end of the vent tube was not submerged in gas, but I checked anyway.

When I removed the gas cap it was a little harder to remove than usual and I could hear that sucking sound meaning there was negative air pressure in the tank. The vent end was not submerged in fuel.

QUESTION: Could the vacuum in the tank due to fuel leaking into a loosened tank vent connection on the inside of the tank? I notice that after a while the fuel pressure in the system will drop even if the fuel selector is on OFF. I'm thinking that after the aux pump pressurized=s the fuel lines, and then is turned off, and the selector turned to OFF from LEFT, that the tank vacuum pulls the fuel back into the tank.

I hooked up a flexible hose to the air vent intake and blew through it. I could feel air AND fuel coming out of the end of the vent in the tank.

I knew what this meant....

But just to be sure, I put my ear right on the wing over the vent fitting on the inboard side of the tank and blew through the hose and sure enough I clearly heard lots of bubbles.

The vent fitting on the inside of the tank is loose.

Ok so here's The Plan - comments and criticisms welcome:

1) Remove the gas from the tank.

My plan here is to remove the quick drain and drain the fuel into new, plastic 5 gallon fuel cans. I'll have a grounding wire from the plane into the gas itself in the gas can.

I would like to dump some of the gas into the right hand tank.

Question: I plan on using a funnel to drain the gas into the can as well as pour it into the right hand tank:

What size filter mesh would you recommend?

2) After removing the gas, I'm going to remove the wing/fuselage fairing and see if I can remove the T-708 large access plate. I'm hoping I can get my hand and a wrench into the opening and onto the nut, from underneath the airplane. If I can't, then the tank will have to be removed and the access plate would be removed anyway, so no work lost.

3) Unscrew the vent tube fastener completely, clean things up, screw the fastener back on with, possibly, ProSeal.

4) I've read threads here where people suggest using fasteners other than the AN515-8B8 philips head screws. I liked the one suggestion of the fastener that has both hex head WITH the philips.

Question: Would I need a washer with the hex head?

5) Button up the access plate using only ProSeal or Van's Flamemaster.


I've looked at this thread to get an idea of how things may go:

http://www.vansairforce.com/community/showthread.php?t=126019

All comments and suggestions welcome.
 
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Lots of questions - filter screen - just go to the auto paint store and get some paint filters, the finest they have. 100 microns is fine as you just want to prevent transfer contamination.
 
BillL said:
Lots of questions - filter screen

I have a lot to learn ;)

- just go to the auto paint store and get some paint filters, the finest they have. 100 microns is fine as you just want to prevent transfer contamination.
Click to expand...

Excellent... thanks for the tip!
 
Most likely you will find the fitting lose on the vent line where it connects to the bulkhead fitting inside the tank. I have an RV-4 that I bought partially built and both tanks vented fuel out the vents. I found the fitting loose on one side and the ferrule missing on the line in the other tank. You should be able to reach it without removing the tank.
 
tturner said:
Most likely you will find the fitting lose on the vent line where it connects to the bulkhead fitting inside the tank. I have an RV-4 that I bought partially built and both tanks vented fuel out the vents. I found the fitting loose on one side and the ferrule missing on the line in the other tank. You should be able to reach it without removing the tank.
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Hi Tommy,

That's my hope - that I can drain the tank, remove the fairing, then remove the larger access plate, get my hand and a wrench in there from under the airplane, and tighten the connection.

I think I'll start with the borescope though and have a look before I do anything.

Did you ProSeal the outside of this connection? Just tighten it? Unscrew it entirely, first, and then screw it back on?

Thanks!
 
Tank

Unless you have a super duper paint job. Removing the tank is not that big of a job. That would allow much better access to everything.
 
Bob Martin said:
Unless you have a super duper paint job. Removing the tank is not that big of a job. That would allow much better access to everything.
Click to expand...

Yeah the paint is really good. Since I have to remove the access plate anyway I thought I'd try to fix the thing without removing the tank. If I can't, there's no real work lost....I'll move on to removing the tank.

Thanks!
 
Saville

I did not need to use proseal. I just tightened up the loose one. The other side which I said was missing the ferrule also did not have a flare on the line. That was fun flaring a line inside of the tank. I did remove both of the tanks.
 
tturner said:
Saville

I did not need to use proseal. I just tightened up the loose one. The other side which I said was missing the ferrule also did not have a flare on the line. That was fun flaring a line inside of the tank. I did remove both of the tanks.
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Ok thanks.

I'm hoping for just some loose connections. But whatever the problem is, it'll be fixed and done correctly.

Thanks!
 
tturner said:
Saville

I did not need to use proseal. I just tightened up the loose one. The other side which I said was missing the ferrule also did not have a flare on the line. That was fun flaring a line inside of the tank. I did remove both of the tanks.
Click to expand...

I considered doing this to my vent line, re-flaring it... but my mechanic said replace the line, which was probably just as difficult. But he was the one doing the condition inspection.
 
Russ McCutcheon said:
use a funnel like this to drain the fuel into your can https://www.zoro.com/funnel-king-tr...D7fAZA2ZTP74MlzypHkQQaAni38P8HAQ&gclsrc=aw.ds

use this funnel to ad fuel to your airplane from a can http://www.ebay.com/itm/like/150927152235?lpid=82&chn=ps&ul_noapp=true

I think you can do the job without removing your tank, fingers crossed!
Click to expand...


Thanks for the URL's.

I got the Mr. Funnel and used that to drain the tank. I'll use it to fill the tank as you suggest.

I got the access plate screws out and half the ProSeal cut under the access plate before I quit.

It's tight but I'm getting it done.

And yeah fingers crossed that:

a) All it needs is tightening and

B) I can do it without removing the tank.

But if it turns out that I have to remove the tank, I will.

Thanks!
 
The B-nut was loose

Well I got the access plate off. The builder used the cork ring.

I reached in and........

...I could tighten the nut with my fingers. So that's why I heard bubbles in the tank, at that position, when I blew air in the air vent intake.

So now I have to figure out how many turns past finger tight to go...or nut facets.

Then, more problematical, I need to figure out how to install the 2 1/2" fuel line that goes between the fuselage and the access plate....WITHOUT messing up the flares. I have to make a new one as I messed up the flare at one end.

That one is a real head scratcher but there must be a way to work it in as I re-install the access plate/sender assembly.
 
First check that the fitting is made up right, good flare and a ferrule
Second, torque it up to the spec in Van's manual. I doubt if you could over torque it considering its location. Hold the fitting that is in the rib so it does not turn and cause a new leak.
Third, put the cover plate on with Proseal, cork will most likely leak.
Lastly, get some Allen head screws with washers to replace the Phillips head screws that are a major pain to remove or install in that tight place.

If you use the soft tubing Vans supplies, it can be bent by hand enough (after forming) to get it in place without damaging the flare. Put one end on and tighten by hand, bend slightly to give clearance to the other end, loosen the first end slightly and get the nut started on the second and then tighten.
 
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Ok so Major progress on the repair:

The B-nut on the inside of the tank is tight
The new fuel line was made - two actually because the first was a little bit too long.
Access plate installed with ProSeal only (no cork gasket)
fuel line installed but the nuts are just lightly snugged up - letting the ProSeal cure first before I put the final snug on those.
Fuel sender installed and wired. Line from the fuel pump to the sender cleared with air prior to installing the sender - just in case my cleaning of the threads wasn't careful enough and some material got into the hose.

Ok so after the ProSeal cures and the fuel line buts are snugged up, the testing can begin.

At the point of the testing where I fuel up the tank, I'm going to do it in 1 gallon increments and make a measured dipstick since I don't have one. Also going to check the amount in the tank vs what the EFIS displays to see if I need to do a re-cal.

I recall someone in the forum saying they made their dipstick out of a paint stirring stick. Not a bad idea - I'll search the forum for ideas there.
 
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