Thank the paintball people

Thanks to the popularity of the sport of paintball, there are a number of companies that manufacture and sell comparatively inexpensive portable tanks, regulators, and fittings for compressed carbon dioxide or air.

I put together a system for filling water rockets. I describe the system below, to give people an idea what is required to get a portable CO2-tank system up and running.

Parts list

I bought

Was it worth it? Counting shipping charges and taxes, I spent about US$270 on the whole enterprise, not counting the CO2 itself. This equipment is definitely more expensive than a bicycle pump, but it sure speeds up the launches. I can pressurize a soda-bottle rocket in a few seconds. The 20 ounces (0.57 kg) of liquid CO2 in the paintball tank expands to about 45 liters of gas at 6.9 bar (100 psi) pressure. This means I can launch up to thirty or so 2L rockets on one fill. Because the tank and regulator are designed for paintball, they are quite portable—I’ve carried them to the park in a backpack. Another thing I like about the system is I can use it in the future to fill high-pressure rockets. Liquid CO2 can deliver approximately up to 60 bar (870 psi), with the value depending on the temperature.


Shown below are the small and big CO2 tanks. Attached to the big tank is the fill station. I changed it so that the small tank connects to the filling station or to the pressure regulator with a quick-release fitting. The main trick for getting the liquid CO2 to transfer from the big tank to the small tank is to make sure the small tank is colder than the big tank. You can do this by exhausting gas from the small tank into the atmosphere, which cools the tank down. My own invention is instead to put the small tank in the freezer for 30 minutes before filling it. If the big tank does not contain a siphon tube, then it must be inverted to get the liquid out. My fill station came with instructions and safety information.

small and big CO2 tanks with filling adaptors

Below is a close-up picture of the regulator (the black cylinder-thing). Pressure is adjusted using a hex wrench inserted in the left side. Palmer's Pursuit Shop sells an adjustment knob that permanently attaches to the regulator, if desired. I installed an on-off valve leading to the delivery line. I fill rockets by turning the valve on and off while leaving the regulator at a set pressure.

adjustable pressure regulator with gauge and on-off valve

The cut-off end of a bicycle pump is attached with a hose clamp to the end of the delivery line.

pressure regulator attached to delivery line