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01-09-2014, 09:41 AM
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Join Date: Oct 2009
Location: Houston
Posts: 65
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Damaging the tanks
Tried to use the tank testing kit with a ballon on the vent line. Short version is the balloon didn't blow up until all of a sudden it got two feet long and shot across the room. This was after a dozen pumps from a large bicycle pump. Probably put a lot more than 1" of pressure in the tank.
Is that likely to damage the sealant?
__________________
Mark Jackson
Houston, TX
RV-8 in progress/Mooney in the hangar.
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01-09-2014, 09:49 AM
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Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,563
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Quote:
Originally Posted by Mark Jackson
Tried to use the tank testing kit with a ballon on the vent line. Short version is the balloon didn't blow up until all of a sudden it got two feet long and shot across the room. This was after a dozen pumps from a large bicycle pump. Probably put a lot more than 1" of pressure in the tank.
Is that likely to damage the sealant?
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No. Just think about that balloon as the pressure relief valve. It just popped off as designed.
I would suggest trying again but going slowly on the pump. Because of the large space you are pressurizing it will take a bit of time to get to pressure but when it reaches it the balloon will go fast. Once you see the balloon starting to expand go even slower, or better yet, stop pumping all together and observe the balloon. If you think it needs more pressure just do one pump and observe again. repeat very slowly at that point. You really do not need to have a large amount of pressure to be able to see leaks thus the recommendation to not exceed 1 psi.
Last edited by RVbySDI : 01-09-2014 at 09:56 AM.
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01-09-2014, 10:21 AM
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Join Date: Mar 2008
Location: Seattle
Posts: 1,412
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I used a U tube manometer. I made it from clear Tygon tubing. It reads instantly and accurately.
I used water with food color for the calibrated indicator fluid. 
27.7 inches of water = 1 PSI.
You could pump this up more carefully, and read the result for days, observing the change in volume from temperature changes. 
__________________
Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)
2019
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01-09-2014, 10:22 AM
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Join Date: Mar 2008
Location: Dublin, CA
Posts: 1,261
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I used an old bike pump to test mine too. The balloon does start expanding all of the sudden. You just have to go slowly. You might have a "better" pump than mine to that transition from the balloon being just barely inflated to fully expand might go very quickly. It was a little startling to me the first time it happened.
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Ray Tonks
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01-09-2014, 10:36 AM
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Join Date: Jul 2007
Location: Cypress, TX
Posts: 526
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I also did what Shipchief describes and used a manometer. I believe it will give a better read than the balloon method because balloons are porous and will leak down over time. When I leak tested, I saw changes in atmospheric pressure reflected in the water level over a 24 to 36 hour period. It acted like a barometer. It is a more accurate measure in my opinion.
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01-09-2014, 10:54 AM
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Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,002
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How do you know when a change in the manometer reading is from an atmospheric (barometric) change or from a leaky tank?
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01-09-2014, 10:57 AM
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Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,563
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Quote:
Originally Posted by blueflyer
How do you know when a change in the manometer reading is from an atmospheric (barometric) change or from a leaky tank?
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Agreed! The manometer is not a leak detection tool. It is a barometer. You need to pressurize the tank and use a soapy water solution sprayed with a mister over all joints and observe for leaks while the tank is pressurized. You could have a very small leak that the manometer would never detect if you solely rely on it to tell you of leaks.
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01-09-2014, 11:05 AM
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Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,692
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I used a manometer
The first few times, you learn where the major leaks are, such as the caps or threaded fittings that are not tight. They leak bad so are easy to identify.
Once you get past that, leave it for a long time. I had two physical things that came into play and had to be dismissed.
1) The tank may have stretched (elastically) because the pressure went down a whit soon after sealing it. I could watch it drop and then stop.
2) Overnight it went down more. AND THEN WENT UP. Definitely thermal influence.
My tanks are fine. No blue streaks after 200 hrs.
Quote:
Originally Posted by RVbySDI
Agreed! The manometer is not a leak detection tool. It is a barometer. You need to pressurize the tank and use a soapy water solution sprayed with a mister over all joints and observe for leaks while the tank is pressurized. You could have a very small leak that the manometer would never detect if you solely rely on it to tell you of leaks.
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That assumes you are constantly inputting air to the tank. Same applies to the balloon system. If you continue to input air at the same rate as the leak, the balloon will not change. If you stop pumping, the manometer and balloon systems will act identically.
Both systems (soapy water and manometer/balloon) are useful in leak detection. With a manometer failure, the soapy water system can tell you where it is. While it is a personal preference, I would not rely on soapy water by itself. Water immersion on the other hand.... 
__________________
Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.
Last edited by rzbill : 01-09-2014 at 11:15 AM.
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01-09-2014, 12:43 PM
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Join Date: Aug 2010
Location: Wichita, KS
Posts: 1,958
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Quote:
Originally Posted by blueflyer
How do you know when a change in the manometer reading is from an atmospheric (barometric) change or from a leaky tank?
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Call your nearest AWOS or ASOS and note the local altimeter setting upon first pressurizing the tank, when using a manometer. Then at future readings, do the same and note the difference. Convert the difference between altimeter settings from inches of mercury to inches of water (google). If that explains 100% of the observed change while keeping temperature constant, then your tank is leak-free.
This is best done inside where the temperature can be held constant. If performing the test outdoors or elsewhere that the temperature also fluctuates significantly, you will also need to compensate for temperature changes. PV=NRT.
Or just leave it for several days. If there is a leak the water will eventually equalize, rather than fluctuating up and down with atmospheric temperature and pressure changes. Leaks will be (very) painfully obvious.
__________________
Kurt W.
RV9A
FLYING!!!
Last edited by krw5927 : 01-09-2014 at 12:49 PM.
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01-09-2014, 01:06 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Quote:
Originally Posted by krw5927
Call your nearest AWOS or ASOS and note the local altimeter setting upon first pressurizing the tank.
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You need to use the local barometric pressure, not the altimeter setting. (close to sea level it won't make much difference)
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