Paintball markers require some form of propellant to fire paintballs. CO2 and compressed air are common propellants and bulk cylinders tend to be cheaper than compressed air which make them a common choice for players that wish to fill their tanks at home. Refilling a CO2 tank is a quick process that can be done in the field with just a few pieces of equipment.
Verify that the bulk CO2 tank is marked "dip tube" or "siphon tube" before continuing. Paintball tanks require partial liquid fills and dip tube bulk tanks take the liquid accumulated at the bottom of the tank via the dip tube or siphon.
Verify that the paintball CO2 cylinder has been "hydro tested" within the last three to five years according to the service sticker located somewhere on the cylinder. Hydro testing is a professional service that tests the serviceability of the CO2 tank and helps avoid injury caused by weakened tanks rupturing under pressure.
Insert the O-ring seal into the valve assembly on the CO2 refill kit that attaches to the bulk CO2 tank and screw the refill kit onto the CO2 tank. Tighten the kit with a crescent wrench to ensure a good seal.
Set all valves to the OFF position before proceeding. This includes the valve for the main CO2 tank, the cut-off valve and the bleed valves on the refill kit, and the valve on the nozzle attached to the fill hose.
Attach the paintball CO2 cylinder to the refill kit via the nozzle at the end of the fill hose.
Hang the CO2 cylinder from the hanging scale and open the bleed valve to purge any CO2 inside. Close the bleed valve once the cylinder is empty.
Change the scale's units of measure to ounces and zero out the scale once any excess CO2 has been purged and the tank is completely empty.
Fill the cylinder by opening the main CO2 tank valve and then the cut-off valve on the refill kit. The cylinder should fill to approximately half capacity before the equalised pressures between the main CO2 tank and the paintball cylinder detain the process.
Close the main CO2 tank valve and the cut-off valve, then open the bleed valve to purge the tank once again. Close the bleed valve once the cylinder has been completely purged. This will drastically reduce the temperature of the cylinder, which is necessary to achieve a full capacity fill.
Open the main CO2 tank and the cut-off valve to fill the paintball CO2 cylinder. Fill the cylinder to one ounce under the printed capacity of the cylinder for safety reasons. Fill a twelve ounce tank with eleven ounces of CO2 for example.
Close all valves and unscrew the filled CO2 cylinder from the fill hose.
Safety goggles should be worn at all times when filling CO2 tanks because tanks can burst under pressure. Always fill the tank to one ounce under the printed capacity to allow for pressure changes due to an increase or decrease in temperature when moving the tank from one climate to another.