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Date: Tue, 27 Jan 2009 18:46:23 -0500
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From: "Ted Noel" <tednoel@cfl.rr.com>
References: <list-3452705@logan.com>
In-Reply-To: <list-3452705@logan.com>
Subject: Re: [LML] Re: Fuel Tank Testing
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Bob,

I'm glad you mentioned the vacuum cleaner in the end of your post. I tested 
my tanks with a ShopVac. After sealing carefully all openings (reversibly!), 
I attached a ShopVac. It pulled about 3" of negative pressure. I measured 
this with a fuel system pressure gauge. Having pulled this relative vacuum, 
I used a ball shut-off valve from an air tool system to seal the system and 
shut off the ShopVac. 24 hours later, I still had 3" of vacuum.

Ted Noel
N540TF

----- Original Message ----- 
From: "Robert Pastusek" <rpastusek@htii.com>
To: <lml@lancaironline.net>
Sent: Monday, January 26, 2009 7:42 AM
Subject: [LML] Re: Fuel Tank Testing


> Bryan wrote:
>
> I am in the middle of testing my fuel tanks for leaks with a vacuum
> pump.  How long is long enough to hold vacuum to prove it wont leak?
>
>
> Be very careful with the vacuum pump. More than one Lancair builder has
> "imploded" his wing tanks with this not-so tried and true method. There 
> have
> also been several mishaps from people trying to use compressed air to test
> for leaks. This method is almost certain to provide comic relief to
> others...don't even consider it. You might, however, consider an 
> alternative
> method that worked well for me:
>
> Carefully seal all openings/vents, etc except one--the fuel pickup port, 
> or
> the return line work well because you can provide it with a very air-tight
> fitting to your "test rig." Make a test rig from a good-quality latex
> balloon--the kind used for filling with helium are generally OK--and a 
> short
> piece of aluminum pipe with a fitting that will attach to your fuel tank
> opening. CAREFULLY seal the balloon to the pipe. RTV on the pipe, and a
> rubber band wrapped over the neck of the balloon to hold it tightly to the
> pipe works well. Blow up the balloon and twist the neck to keep the air
> inside while you attach the fitting end to your tank. When you allow the
> balloon to un-twist, most of the air will rush into the tank until the 
> (very
> small) pressure is equalized, but the balloon needs to remain partially
> inflated. You may need a couple of tries to get it right... You have a
> fuel-tight tank when the size of the balloon changes with the barometric
> pressure over 2-3 days, but does not go flat during that time.
>
> You can make a fancy test rig with a Tee and valve, etc, to aid in filling
> the balloon, but everything you add must be absolutely air tight or you're
> adding complications with negative benefit. I can't over-emphasize the 
> need
> for careful sealing of all openings/fittings. For example, I used clear
> packaging (release) tape to seal the filler cap opening on my tanks. Since
> the cap was larger than the width of my tape, I used two strips, carefully
> overlapped and pressed down. My balloon went flat in about two days. 
> Double
> checked every joint/connection and opening with soapy water and concluded 
> I
> had a leak in the tank, but before proceeding with "dunking the wing" to
> find it, I tested the second wing tank. Same results...a very slow leak 
> that
> deflated the balloon in a couple of days. I then went back with the soapy
> water around the openings and discovered air leaking along the inside edge
> of the clear packaging tape where I'd overlapped them across the top of 
> the
> filler cap. One very small bubble every half minute or so at each end of 
> the
> tape where one strip laid across the other! YGBSM! Anyway, it was enough 
> of
> a leak to deflate the balloon--in time. Re-applied the tape strips with a
> very small wipe of RTV at the edge of the first tape and both tanks tested
> well. The balloon stayed inflated for a week or so for each tank.
>
> Bottom line: This method works well, and is safe to use. The tanks can 
> stand
> VERY LITTLE positive or negative pressure, so no matter what method you 
> use,
> be very careful, and don't even think about approaching your tanks with a
> compressed air hose...or even a vacuum cleaner hose for that matter!
>
> Bob Pastusek
>
>
>
> --
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> http://mail.lancaironline.net:81/lists/lml/List.html


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