Manometer Testing of Fuel Tanks

[az_gila]

..can also affect the manometer levels.

This last weekend we had pretty low pressure with the winds - that returned to normal yesterday.

http://www.wunderground.com/weathers...raphspan=month

This was about a 0.5% change in the effective volume of the air in your tank - throw some temperature changes in too and that water level can easily change without any leaks...

I had the same trouble this last weekend....

[JonJay]

Here we go again with yet another new thing I have never heard of being done on an RV fuel tank. Never ceases to amaze me but obvioulsy I still am learning and have a long way to go.
What advantages does the manometer method have over the dish soap method? I am guessing you can discover small slow leaks better?
I moved my tanks from inside the hangar, temps about 70 to outside in the sun to do the soap test and my balloon, (actually, it was a similar device made of latex that I got out of my sock drawer, achhummm,) and it blew up so fast from the pressure change that it popped! It's not easy to pop those things.
Can you keep a controlled enough environment (temp and baro) for the manometer to perform well?

[Pmerems]

Thanks for all the input. I will try the manometer again once I have completed balloon testing of the tanks.

The first tank showed no sign of any leaks with the bubble test. The balloon remained inflated with only a slight reduction in size over a 20 hour period. Looks good to me.

The second tank showed a very small leak at the outboard baffle/rib seam. That is where the outboard z-bracket is riveted on. I removed a few 1/8" rivets, spread and cleaned the seam and applied new proseal. This is one of the easiest places to fix. Since the leak was very small I was able to bubble test all the other joints, seams and rivets and no other leaks were detected. I will repeat the bubble and balloon test in a few days once the proseal is cured.

I am very optimistic that the tanks will be done in a few days. I will also try the manometer on one tank just to see how it works out.

Thanks for the input.

[RVNineA]

I also recommend the manometer method, once you figure it out, it's very easy to use, and it gives a more quantified measure.

But the comments about local "weather" changes are very true. Soon after I hooked up my first tank, the water level dropped about 1.5-2 inches and I thought I had a leak. But it stabilized at that position, then started to climb back up! It climbed to about 2 inches above its original position. Then it started to drop again. This all took place over a couple of hours, at most. I realized that it was simply responding to the ambient air temperature change caused by the nearby furnance cycling on and off. So I left it hooked up for two full days, and just watched it go up and down the whole time. The range of motion never changed, so I concluded that I had no leaks.

John

[airguy]

Originally Posted by RVNineA

I also recommend the manometer method, once you figure it out, it's very easy to use, and it gives a more quantified measure.

But the comments about local "weather" changes are very true. Soon after I hooked up my first tank, the water level dropped about 1.5-2 inches and I thought I had a leak. But it stabilized at that position, then started to climb back up! It climbed to about 2 inches above its original position. Then it started to drop again. This all took place over a couple of hours, at most. I realized that it was simply responding to the ambient air temperature change caused by the nearby furnance cycling on and off. So I left it hooked up for two full days, and just watched it go up and down the whole time. The range of motion never changed, so I concluded that I had no leaks.

John

I had the same experience - I connected my manometer in my workshop one evening (about 90 degrees) and left it overnight. I checked it the next morning (about 65 degrees) and was heartbroken to see that it had dropped A LOT. I finally figured it out when later that day it had risen again, so I put it in the house for temperature stability, left it to settle for a couple hours, then marked the fluid level and noted the altimeter setting at that point. I watched it for two days taking into account the local altimeter, that made it easy.

[mcencula]

...1 psi is only about 27.7 (let's call it 28) inches of water. This means that the water level in the left tube of the U will be 28 inches different from the water level in the right tube of the U. So, starting from neutral, one side will go down 14 inches which will push the level in the other side up 14 inches.

Temperature will affect the level by roughly .82 inches of water per degree F. So, say you start the test at 70 degrees and pump up the tank (using the aforementioned schrader valve) to 28 inches, then wait a couple hours. If the temperature has gone up to 71 degrees, you should expect to see 28 + 0.82 = 28.82 inches of water.

More info here.

Good luck.

[AndyWW]

Not sure which thread to resurrect but I picked this one. I completed my tanks before Christmas, but have yet to definitively conclude whether they are leak free.

I used a water manometer and soap solution. After using packing tape and fuel lube to seal the filler caps, and some fuel lube on the Vans bicycle valve in the fuel drain hole (leaks I discovered with soap solution), I got the pressure to hold well. I did 3-day tests on each tank and found that althought the water level goes up and down like a yo-yo, after taking account of atmospheric pressure and temperature variations there was no evidence of a leak. However I then decided to do a longer test on the left tank, and after almost 2 weeks the water level in the manometer was about 1.25 inches lower than it should have been. (I did a regression in Excel of the water column level against the time, pressure and temperature.)

So I got out the soap solution and found.... nothing.

Now I am a bit stumped. It is possible that some of the change in level is due to evaporation from the open top of the manometer tube - my shop has a dehumidifier and is typically 21C and 40% humidity. I am going blind staring at soap-covered seams and proseal blobs looking for bubbles.

Three questions for the collective intelligence:

1) Exactly how sensitive is the soap test? I found a leak at the bicycle valve fairly easily due to seeing bubbles actually growing in front of my eyes. But if there was a really slow leak, would the soap test be expected to find it?

2) Is there anything else I could try short of filling the tanks with avgas? I do have a hot-tub but that seems like a method which could be a bit risky, especially when you consider how hard it must be to hold a tank underwater!

3) Anyone know what the evaporation rate would be for water out of the end of a tube in an indoor warm and dry environment?

Thanks in advance.

[daveyator]

Trust the soap.
DaveH

[Bill Boyd]

...another manometer not connected to anything, same diameter tubing, in same room. As a guy who maintains a humidor in a heated space in winter, I can tell you that water loss to the ambient air can be surprising. over an inch of column in two weeks doesn't sound excessive for evaporation at all to me.

I'm still puzzling the relationship of headspace air in the tank and manometer tubing to reliability of readings - doing thought-experiments while waiting for the coffee to kick in. Something seems amiss with the entire notion, but can't finger just what, yet.

[diamond]

I just tested my tanks as well and had the same concerns. I saw no leaks with soap water test. I concluded that if there were leaks too small to detect with soap water, then they are probably also too small to be of any concern with fuel in the tanks. Is this an accurate assumption?