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  #1  
Old 05-31-2016, 08:12 AM
Saville's Avatar
Saville Saville is offline
 
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Location: KBVY Massachusetts
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Default Fuel System Problem #1 - The case of the dripping tank vent

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/communit...d.php?t=126019

All comments and suggestions welcome.
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Last edited by Saville : 05-31-2016 at 08:33 AM.
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  #2  
Old 05-31-2016, 10:49 AM
BillL BillL is offline
 
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Default

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.
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  #3  
Old 05-31-2016, 12:33 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by BillL View Post
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.
Excellent... thanks for the tip!
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  #4  
Old 05-31-2016, 07:25 PM
tturner tturner is online now
 
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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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  #5  
Old 06-02-2016, 10:30 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by tturner View Post
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.
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!
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  #6  
Old 06-02-2016, 10:54 AM
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Bob Martin Bob Martin is offline
 
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Default 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.
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  #7  
Old 06-02-2016, 10:56 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by Bob Martin View Post
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.
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!
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  #8  
Old 06-02-2016, 12:58 PM
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edneff edneff is offline
 
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I had a similar problem, the fitting on the inboard side of the vent line was flared improperly and I had to replace the vent line... complicated! Here's the relevant thread:

http://www.vansairforce.com/communit...ad.php?t=81517
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  #9  
Old 06-02-2016, 01:05 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by edneff View Post
I had a similar problem, the fitting on the inboard side of the vent line was flared improperly and I had to replace the vent line... complicated! Here's the relevant thread:

http://www.vansairforce.com/communit...ad.php?t=81517
Before it was fixed, did you notice anything odd about the fuel pressure reading?
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  #10  
Old 06-02-2016, 08:01 PM
tturner tturner is online now
 
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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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