On/off valve system allows you to control the flow of CO2 into your paintball gun. This is handy, as you can turn off the tank, fire out the remaining pressure inside your paintball gun, then easily unscrew the tank without releasing a gout of cold gas (which usually makes your tank o-ring practically useless from the extreme temperature changes). As soon as you turn on the valve, unregulated CO2 flows into your paintball gun (about 800psi).

Simply screw the CO2 tank into your paintball gun, open the on/off valve, and you're ready to go.