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NOTES ON CO2 FILLING

 

Finding the correct supply bottle
A five to ten pound supply cylinder is ideal to recharge your small rifle/pistol cylinders at home. They are usually obtainable from fire extinguisher shops and cost between $75.00 and $150.00 depending upon condition, new or used and size. The bottle must be fitted with a standard wheel valve and a dip tube [siphon tube] inside the bottle if you are going to use it standing upright. If you want to invert the cylinder [hang it on the wall or the like] a dip tube should not be used. The dip tube is simply a copper tube that runs from the wheel valve at the top down into the bottom of the cylinder, its purpose is to pick up the liquid CO2 from the bottom of the tank instead of the gas from the top of the tank. Cast iron bottles are acceptable provided only that they are clean and free from rust inside. Aluminum bottles are better only because they usually stay cleaner inside. Size of the supply bottle can be determined by price and the frequency that it will need to be refilled by the dealer. The following will approximate the number of fillings that you could expect from the supply bottle to the small cylinder;

 
5 pound 60 fillings [pistol] 22 fillings [rifle]
10 pound 120 " " 44 " "
20 pound 240 " " 88 " "

There is about 10% gas loss in the filling process.

Safety considerations

Don’t mess around with pressurized CO2 !! You are dealing with about 800lbs. of pressure…..treat it with respect …..it can give you a nasty gas cut or worse if your fingers or hands are exposed to it. Do not try to add any fancy “plumbing” to any of the fittings, tell the dealer exactly what you are doing and take his advice on the correct fittings to use. Connect the brass adapter fitting that comes with your rifle/pistol directly to the wheel valve and leave it there. Never subject either the supply bottle or your small cylinders to temperature extremes [never over 40 degrees celsius]. Pressure rises dramatically with temperature…..be very carefull not to overfill the small cylinder, in fact it is better to underfill than overfill. Do not push the valve stem on the small cylinder with a screwdriver or the like…..use the small gas discharge nipple which is usually supplied with the gun if you wish to discharge gas. Read your owners manual before doing anything. The large cylinders should be stored in such a manner that they cannot fall over with the possibility of breaking off the wheel valve. This applies especially to the huge 100lb. cylinders often seen at the club. They all need to be tied up, tied down or otherwise set so that they cannot fall over, Can you imagine what a rocket one would have on his hands if the top ever got broken off in an enclosed room ?? It is easy to build a small wooden box around a smaller supply bottle to protect the valve at the top end.

Filling procedures
The filling procedure is very simple and safe if you are not hung up on filling right up to the maximum fill. Simply screw your small cylinder onto the brass adapter on your supply bottle, open the wheel valve for a half a minute and close it. Your cylinder will be about two thirds full and good for lots of shots. Fill both cylinders this way and put them in your kit. Underfilling is better than overfilling. If you MUST have a completely full cylinder, life becomes a little more complicated….the maximum filling weight has first to be calculated. First take the TARA [empty] weight stamped on the cylinder, [it is slightly different on every cylinder]. To this figure add the FILLING WEIGHT suggested in your owners manual. The result is the maximum full weight of the cylinder after filling. It must not be exceeded. To get your small cylinder up to that weight it will be necessary to have the small cylinder cooler than the supply bottle. There are two ways to do this; 1. put the small cylinder in the refrigerator for a while to cool it, do not freeze it because there is a danger of over-hardening the seals. 2. blow off some gas from the small cylinder using the discharge nipple, this cools it. The latter way wastes gas. To do all of this you will require accurate scales to do the weighing. My recommendation is to use the first method which is quicker, simpler, safer and you don’t need scales. After a while you will get used to the number of shots that you are getting from a “warm” filling and you can forecast when refilling is necessary before the cylinder empties. Some cylinders are fitted with a safety disc which will blow if the cylinder is overcharged [Walther for example] and some are not.

The physical properties of CO2 gas

Read you encyclopedia for the complete story on the properties of CO2 gas it is interesting reading. The main feature that we need to know about it is that it is a liquid when pressurized in a tank, when the pressure is released it turns to gas. This conversion from gas to liquid and back takes place at about 800psi. The pressure remains the same in your cylinder so long as there is liquid in the cylinder…..each time a single shot uses up some pressure, a little liquid converts to gas and the pressure goes immediately back to 800psi. This feature, of course, is why CO2 makes such a good propellant….. we have a built-in constant pressure source. Air does not do this and regulator valves are necessary to control the pressure. There are no pressure valves in the CO2 guns, the natural features of the gas do the job for us. Remember that the pressure will change slightly with room temperature, its not a lot, but try to shoot your match under reasonably constant temperature conditions.

Air transport

Even though CO2 is used to put out fires the airline people will go bananas if they find out that you are transporting any kind of pressurized gas. They treat it like a bomb. It is absolutely necessary to empty your cylinders before air travel and be prepared to show them that they are empty [by pressing the valve stem]. You will also have to know that there is CO2 available at your destination. These days most of the large clubs are providing CO2 right on the range.

Get accustomed to CO2, it is still the best propellant in my opinion and it is here to stay. If you think it is a bit of a nuisance, remember the hard cocking, adjustments and repair to the old manual cockers.

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