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Author Topic: Tank failure?  (Read 244 times)
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Duncan McBride
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« on: July 02, 2020, 07:23:47 PM »

I was flying a free flight model with a G-160, brand new.  I was test flying and all the charges were gas charges from a 20 oz. paintball tank that was nearly empty.  On about the fifteenth flight or so, I filled the motor tank at the back of my van, where everything was in the shade, and walked out to the middle of the field to launch.  I was holding the plane upright at the level of my shoulder as I was walking when the tank burst apart.  It was like a rifle shot, making my ear ring on that side.  The top of the tank with the cap and filler valve was blown somewhere out in the field and never found.  The bottom part of the tank blew through the fuselage and into my thigh tearing my pants and raising a nasty bruise.  I've looked at the tank and it appears the top is screwed into the bottom with some kind of thread locking glue.  The joint failed.   Has this ever happened to anyone here or have you heard of it? This is worrisome.
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billdennis747
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« Reply #1 on: July 03, 2020, 12:03:23 PM »

That does sound bad. Are you saying the top is screwed in and glued - not just glued? If screwed, how did it blow out? Did it destroy the thread on its way out? I gave up on Telcos first time round because I didn't trust the chargers - stories of them exploding apart in pockets.
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Duncan McBride
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« Reply #2 on: July 05, 2020, 08:08:00 AM »

Here is a shot of the tank that failed.  You can see the threads.  The darker grey streak appears to be the sealant/adhesive.  The threads are pretty shallow but it is a thin-walled tank and I can't tell if they were damaged or not.
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Duncan McBride
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« Reply #3 on: July 05, 2020, 08:11:46 AM »

Here it is next to another tank the same size.  I think they are 5cc tanks. They came with the 2 Gasparin g160s I bought from Old Engines. Jiri confirmed that a sealant is used on the threads and the tanks are tested to higher than operating pressure.  I will send him these pictures as well, and offer to send the tank back if he wants to inspect it.
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raggedflyer
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« Reply #4 on: July 05, 2020, 11:12:46 AM »

In my opinion the mechanical joint between male and female threads should retain the parts together at the highest operating pressure plus a safety factor also taking in consideration the worst combination of operating temperature. The sealant should be to eliminate leakage and may add some additional joint strength but should not necessarily be relied upon because the strength will vary with temperature and is probably affected by thermal cycling.

The cut thread in the vessel looks more like a scratch thread and perhaps not full depth and has stripped on the left side.

Be interesting to learn if these pressure vessels are 100% over pressure tested or only a representative sample tested.
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pedr01
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« Reply #5 on: July 05, 2020, 12:13:40 PM »

Just throwing a curveball out there. Could it be that your paintball tank is High Pressure Air and not CO2?

Pressure in a CO2 canister is typically 850psi. If there is more CO2 in the cylinder, it will then be converted into a liquid form.

Whereas pressure in a high pressure air canister is typically 3000/4500psi. Big difference.
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billdennis747
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« Reply #6 on: July 05, 2020, 12:28:34 PM »

Crikey! But then wouldn't the motor run much faster (until it blows up)?
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Duncan McBride
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« Reply #7 on: July 05, 2020, 04:24:25 PM »

No, the tank was filled at a sporting goods store with CO2 about two years ago.  Used on and off ever since with several motors, no problems.  Doing some internet browsing I found that 850 pound number as well, the partial pressure of gaseous CO2.  The article went on to say how dramatically the pressure rises with temperature.  I sent the pictures to Jiri, and I hope he wants to have the tank returned - it would be good to find out whether he thinks there was some issue with the tank or if temperatures above 90F with exposure to direct sunlight is beyond the capability of the tank.  I'll let you know what I find out.
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FLYACE1946
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« Reply #8 on: July 05, 2020, 07:47:33 PM »

Some people put the co2 tank in an ice chest. I thing at 90 degrees that is a GREAT IDEA. This would be the tank that is used to charge the system.
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