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Still leaking fuel

Old 01-19-2009, 09:51 PM
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fly boy2
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Default Still leaking fuel

I had done an inspection of my tank and found no leaks. So the day after I ran a full tank of fuel and no problems. Today I did a taxi test and after engine quit after a fuel tank; I found fuel coming out the back of my spad deboniar. I'm pretty close to putting a new tank that I bought for another plane and getting fuel lines from my jug and pump. I did enlarge the holes that the lines come out of; I guess we'll see if that did it. I tried to look for a hole in the lines; and found nothin. any suggestion on what it could be.
Old 01-19-2009, 10:11 PM
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Default RE: Still leaking fuel

loose cap?
Old 01-19-2009, 10:15 PM
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Default RE: Still leaking fuel


ORIGINAL: w8ye

loose cap?
or maybe a split seam or pin hole in the tank that only appears under pressure? Did you submerge the tank in water, pressurise with a bicycle pump and check for a stream of minute air bubbles?

Cheers,

Colin
Old 01-19-2009, 10:15 PM
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Default RE: Still leaking fuel


ORIGINAL: w8ye

loose cap?
Am I suppose to be able to pull it out without unscrewing the little screw
Old 01-19-2009, 10:16 PM
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Steve Steinbring
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Default RE: Still leaking fuel

Pull the tank and lines from the airplane. Seal off all but one line, then pressure test the setup with air by submerging in water. If you see bubbles you've got leak, just follow them to the source of the problem.
Old 01-19-2009, 10:18 PM
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Default RE: Still leaking fuel


ORIGINAL: Crash Campbell


ORIGINAL: w8ye

loose cap?
or maybe a split seam or pin hole in the tank that only appears under pressure? Did you submerge the tank in water, pressurise with a bicycle pump and check for a stream of minute air bubbles?

Cheers,

Colin
no but I'll try that; the way I checked for leaks first time was to fill with water and look for leaks
Old 01-19-2009, 10:23 PM
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Default RE: Still leaking fuel

Pressure test under water. I just hold it under with the lines pinched off except for the one, I use a long piece of fuel line on the open end and just blow into the line real hard and hold it while I look for leaks. I sometimes use a retract air pump but that is over kill most the time except for my YS engine takns.
Old 01-19-2009, 11:38 PM
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Crash Campbell
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Default RE: Still leaking fuel


ORIGINAL: fly boy2


ORIGINAL: w8ye

loose cap?
Am I suppose to be able to pull it out without unscrewing the little screw
NO

Cheers,

Colin
Old 01-20-2009, 05:05 AM
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Default RE: Still leaking fuel


ORIGINAL: fly boy2


ORIGINAL: w8ye

loose cap?
Am I suppose to be able to pull it out without unscrewing the little screw

If you can then there's your probem! Tighten that screw real good, then do the under water test that Grey Beard wrote about. Let us know if the plane leakes fuel again or not, then we'll take it from there.
Old 01-20-2009, 06:40 AM
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Default RE: Still leaking fuel

be careful not to over tighten the bung (yes that's its real name) or you'll split the tank at the neck...never ever fill the tank with water....hard enough to get the water out, and water is your enemy....
Old 01-20-2009, 06:47 AM
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Default RE: Still leaking fuel

NO! Don't "tighten that screw real good". It should be snug, but not as tight as you can get it. Doing that will split the neck of most fuel tanks.

I've read that the best method is to put the thing together, then turn the compressing screw in until it begins... BEGINS... to compress and seal the bung in the neck of the tank. It should be snug, but not tight. It should turn slightly, under pressure from twisting by your fingers, but that's just about it. Any more and it will more than likely split the neck of the fuel tank.

I will find the link that describes this to prevent what I expect to be some incoming flack about this. But, I think many of the experts here on RCU will verify that it should not be tightened beyond being snug, enough to slighly expand the bung and seal off the tank, but not tight enough so you cannot turn the bung in the neck. As I said, snug, but not turn easily, but turn with a little effort. How much is that? I don't know, but I do know it should not be so tight that it will not turn.

CGr.
Old 01-20-2009, 09:04 AM
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Default RE: Still leaking fuel

True. It should be snug enough that you can't move it, but not too tight.
Old 01-20-2009, 11:39 AM
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Default RE: Still leaking fuel

I think I read what CG just said but I still tighten mine until I can't twist the bung. I have never split a tank but I have stripped more then one of the plastic backers. After you assemble a few you will get the feel for it.
Old 01-20-2009, 06:20 PM
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Default RE: Still leaking fuel


ORIGINAL: CGRetired

NO! Don't "tighten that screw real good". It should be snug, but not as tight as you can get it. Doing that will split the neck of most fuel tanks.

I've read that the best method is to put the thing together, then turn the compressing screw in until it begins... BEGINS... to compress and seal the bung in the neck of the tank. It should be snug, but not tight. It should turn slightly, under pressure from twisting by your fingers, but that's just about it. Any more and it will more than likely split the neck of the fuel tank.

I will find the link that describes this to prevent what I expect to be some incoming flack about this. But, I think many of the experts here on RCU will verify that it should not be tightened beyond being snug, enough to slighly expand the bung and seal off the tank, but not tight enough so you cannot turn the bung in the neck. As I said, snug, but not turn easily, but turn with a little effort. How much is that? I don't know, but I do know it should not be so tight that it will not turn.

CGr.

60+ planes built, I still have yet to split a tank. Unless you are a over grown gorilla, it takes effort to split a tank. One turn after snug is perfect. "So tighten it real good" still stands.
Old 01-20-2009, 06:27 PM
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Default RE: Still leaking fuel

http://www.rcuniverse.com/magazine/a...rticle_id=1068

Minn's article on "Let's Talk Tanks"

Once everything is correct, tighten the screw. This compresses the rubber stopper so it tightens itself in the neck of the tank, but this is another place you need to be careful. Over-tightening can cause the neck to split! It might happen now, or a month from now, so don't go mid-evil on it. Just tighten it enough so you can't turn the stopper in the neck - this is something you may want to double check after a season of flying.
Old 01-20-2009, 07:01 PM
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Default RE: Still leaking fuel


ORIGINAL: jetmech05

never ever fill the tank with water....hard enough to get the water out, and water is your enemy....

yeah I found that out. ok I have some results and I found that I'm only leaking out the hole where the fuel dot line should be. Is this suppose to happen. I thought I could pull the bung off and could not;but I did twist is with very little effort. I dont know if this helps or not
Old 01-20-2009, 07:31 PM
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Default RE: Still leaking fuel

No... I would replace the line, use a safety razor and try to make a straight cut when you cut your new fuel line. Once you've replaced the fuel line push the male end of the plug in and see what happens. The Plug should be snug in your fuel line. If it leaks at the plug, I would use a fater male plug.

When you bought your plug, I'm sure it came in different sizes? Use a thicker male end Plug and change that part of the fuel line and see what happens.

I've had problems with plugs leaking in the past... after a while the fuel line weakens (from pluging and unplugging) resulting in leaks.

I use Kwik-Fill, they seem to be better. It just takes a bit of maintenance if I store my plane for a while. I have to squirt After Run Oil or Castor Oil in the Kwik Fill to keep the spring and gasket from sticking.

http://www3.towerhobbies.com/cgi-bin...&I=LXD745&P=ML

http://www.horizonhobby.com/Products...?ProdID=DUB334

Hope that fixes you problem.
Old 01-21-2009, 01:02 AM
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Default RE: Still leaking fuel


ORIGINAL: LuftwaffeOberst


ORIGINAL: CGRetired

NO! Don't "tighten that screw real good". It should be snug, but not as tight as you can get it. Doing that will split the neck of most fuel tanks.

I've read that the best method is to put the thing together, then turn the compressing screw in until it begins... BEGINS... to compress and seal the bung in the neck of the tank. It should be snug, but not tight. It should turn slightly, under pressure from twisting by your fingers, but that's just about it. Any more and it will more than likely split the neck of the fuel tank.

I will find the link that describes this to prevent what I expect to be some incoming flack about this. But, I think many of the experts here on RCU will verify that it should not be tightened beyond being snug, enough to slighly expand the bung and seal off the tank, but not tight enough so you cannot turn the bung in the neck. As I said, snug, but not turn easily, but turn with a little effort. How much is that? I don't know, but I do know it should not be so tight that it will not turn.

CGr.

60+ planes built, I still have yet to split a tank. Unless you are a over grown gorilla, it takes effort to split a tank. One turn after snug is perfect. "So tighten it real good" still stands.
This is why I use hayes tanks, now screw or seem to split or screw to come loose. The problem comes when you want to defuel a plane with a cowl, then you have to use one of those external bypass things from World Models.
Old 01-21-2009, 02:23 AM
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Default RE: Still leaking fuel

If you use a Sullivan or Dubro, or Hayes tanks overtightening isn't really a problem. Where it comes into play is the sub-standard ARF tanks. You want the bung tight enough that the tubing doesn't move easily, and that you can't pull the bung out of the tank by hand.

There is very little pressure or vaccum on the fuel system. Any thing you can do with your lungs to induce a leak should be fixed, but more that that, I wouldn't worry about. The most likely culpurt in fuel tank air leaks is the clunk to brass tubing line. Some of the flexable tubing that is supplied with tanks today are not very reliable.

The two fuel tank problems I've had in the last four years are both related to ARF tanks. One split after over 100 flights, and on the other, the flexable line to the clunk broke in half. Once I have set up a Dubro or Sulivan tank, I've not had any problems with it.

Just make sure that the ends of the brass tubing are not sharp. Use a fine file and cut the sharp edge off first. Clean any filings out of the tubing and the assemble the tank.

Don
Old 01-21-2009, 05:49 AM
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Default RE: Still leaking fuel

If your leaking fuel out of the bung where the fill line is...then you need a new bung...might as well get a new tank...gotta be careful inserting brass lines in the bung...make sure they don't have a burr on them that would enlarge the hole and cause a leak....
Old 01-21-2009, 09:43 AM
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Default RE: Still leaking fuel


ORIGINAL: fly boy2

I found that I'm only leaking out the hole where the fuel dot line should be.
Are you saying that the thrid hole in the bung was once opened (They are closed when new) but there is not a brass tube in it? If so, that's the problem.

You can replace the bung, or you could just stick a piece of 1/8" solid rod in that hole (Or a piece of brass tube that has been soldered closed)
Old 01-21-2009, 01:52 PM
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Default RE: Still leaking fuel

having read all the replies to your problem all contain answers for you. If you follow their advice and still have any problem throw the whole tank etc. away and get new. Be sure to follow the advice given.
Old 01-21-2009, 02:02 PM
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Default RE: Still leaking fuel

I pitch any tank with bungs and screws and brass tubes! Buy a Hayes tank and none of these issues.
Old 01-21-2009, 05:06 PM
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fly boy2
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Default RE: Still leaking fuel

I finally found the problem. The screw wasnt on tight enough[:@]. After tightning the screw I put the tank under some water and pressurized the tank with my lungs and no bubbles[8D]. I cant believe all the trouble over a loose screw; I learned my lesson. Hopefully I get to fly sun.. Thanks Ya'll
Old 01-22-2009, 11:10 PM
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Default RE: Still leaking fuel

Wahooo! You see, it's the little things that cause the most problems, WE are glad your issue with the leak is now fixed.

Keep the wings level,

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