RCU Forums - View Single Post - Plugging the tank vent line, yes or no?
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Old 10-20-2017, 12:04 PM
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Join Date: Jan 2002
Location: Cudahy, WI
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I have a Kevlar tank in my jet, I always plug the line. I have never noticed any air entering or leaving when I pull the plug even with a +40F temp change. I store the jet in the basement so I want no fumes. I bought my jet used 11 years ago and this is still the same tank with no cracks or other issues related to pressure differences. I did one time have an issue after filling the take at home while doing some maintenance and then going to the field i did not have to fill it so I forgot to remove the plug. Started fine, took off fine but the available power was steadily dropping as I flew. It was about 2 or 3 minutes into the flight that it hit me so I killed the turbine and made a dead stick landing. There was a huge rush of air when I pulled the plug but no damage to the tank or other components. I find it hard to believe that just a small temp change could create enough pressure or vacuum to damage anything.
My tank is rectangular and is not a tight fit into the air frame. I can see where a round tank or one that is a tight fit will create more pressure change with the temp change. round will hold shape better against both pressure and vacuum, rectangular will allow the sides to bulge a bit to relieve some of the pressure change.
Now if the tank was full with little to no air and you had a big temp change then I could see the hydraulic pressure doing some damage.

Anyone have a little pressure gauge to do an actual measurement of the pressure change with temperature?