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CO2 Tank System
 

Speaking of normal tank pressures, I'll pass along the details of a situation I experienced just last summer.  It involved a trip to the local welding supply store that I had been frequenting for a number of CO2 refills.  The weld shop was only about 3 miles from my house and unlike many shops, they would fill your tank while you waited.  Many of the other shops would only exchange your tank for a filled tank.  When you have a nice aluminum tank with a cool carry handle on it, the last think you want to do is exchange it for beat to crap steel tank.  Because of this, I continued to use this shop for my refills.

It was mid summer, which means it was over 110 degrees, here in Phoenix.  I stopped by the weld shop and they filled my 10# tank.  I drove home and set the tank on the work bench in the garage.  About 3 or 4 hours later, I heard this roaring noise that sounded just like a freight train.  It took me a couple of seconds before I realized what it had to be.....my freshly filled CO2 tank had cut loose and was venting excess pressure.

Now you have to realize that the excess CO2 gas does not simply vent until it is back to a safe pressure....instead, it begins venting and continues until the tank is completely empty (and not to mention cold enough to freeze the brass nuts off a steel bridge!). 


Here is a picture of the safety relief that all CO2 tanks have.  Yours may look a little different, but it will serve the same purpose....if the pressure gets too high, it will blow out and release pressure. 
 

If it ever should blow, you will have to replace it.  They unscrew from the valve assembly and the business end of it looks like this.  The hole is the result of the pressure building up and eventually rupturing the thin metal burst disc.  My relief was rated at 3000 PSI.....WOW....that is a bunch of pressure when you consider that the normal working level is around 700 PSI.  What caused the pressure to spike so high?

A 10# CO2 tank will hold 10# of CO2 when it is properly filled.  I stress the word properly because an overfilled CO2 tank, when subjected to summer time temperatures, will quickly build up enough pressure to blow out the 3000 PSI burst disc.  When my burst disc blew, I contacted the company who had built my tank (for a replacement) and spoke with one of their top employees.  By then, I had heard all manners of horror stories about CO2 tanks blowing up in the Phoenix summers, etc.  He assured me that a properly (there is that word again) filled CO2 tank can be half buried in the Mojave desert, all summer long, without any chance of it venting.  It is not until the tank is overfilled AND ambient temperature is high that the recipe for a blowout is cooked up.  I found some related CO2 tank filling info on the Internet but I will admit it was too technical for me to fully grasp.  It went into detail as to how the pressure spikes, based on the percent of overfill and the temperature (among other things discussed).  I was able to glean enough from it that I felt comfortable with what the gas tech guy told me on the phone.


By now, you should be asking yourself how YOU are going to avoid getting yourself into this kind of situation.  After all, you are putting significant faith into the abilities of someone that you probably don't know and hopefully can count to 10 when he fills your CO2 tank.  One thing that I was NOT doing before my tank venting scenario but now do after fill up is to simply weigh the tank.  The above shows the tare (empty) weight of my aluminum tank, which is 14.5 lbs.  That means that the tank should weigh 24.5 lbs. after it is filled.  If it weighs more than that, I would hook up the regulator and hose and bleed some CO2 off before the burst disc decided to do its thing.  Just weigh your tank before you take it to the store for a refill and immediately weigh it when you get home.  I would suggest that you don't do this first thing in the morning and then not plan on weighing it until later in the afternoon.  On a warm day, that will be more than enough time for the pressure to build on an overfilled tank.  Please understand that I am NOT attempting to scare the dickens out of you and keep you from using a CO2 tank.  Actually, it is quite the contrary.  I want you to be fully aware of a CO2 tank's operation so you can properly use it without fear of it having a problem.

CO2 is an outstanding portable air source.  My used CO2 system ran me $100 (tank, regulator, and hose).  I've used it on the trail, in the garage, in the house, and at the parking lot.  If you decide to go with a CO2 tank, I hope you enjoy yours as much as I have mine.

P.S.  In case someone was wondering, I stopped using that welding supply shop.  I went back the following day and requested a refund of my money.  I was politely informed that it was my fault the tank over-pressured.....the idiot behind the counter claimed I should not have stored it in my garage.  I asked him about all of the CO2 bottles at his store that sat outside in a non air-conditioned storage shed....DUH.....he couldn't think of a good come back for that one!   I now have my tank filled at a commercial fire extinguisher shop....they have yet to be a problem....and one of the employee that works there thinks my TJ is pretty nice.  How can I go wrong?

 

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