Fuel For A Paintball Marker
The Reason that people need a tank when they play paintball is because you need a way to force the paintballs out of the gun and this cannot be achieved effectively by just using a spring. What they decided to do was to fuel the paintballs by pushing them with a gas. The way in which they did this was to put the gases, either Oxygen, Carbon Dioxide or Nitrogen un extreme pressure until they turned into a liquid and once they are in a liquid form they can be blown into a tank which probably looks something like this.
Carbon Dioxide must be under a pressure of at least 415.8 kPaA For it to turn into liquid form. Oxygen and Nitrogen are very similar to this.
The way in which the gas is let out is that there is a needle in a valve in the top of the tank and when the tank is screwed into the paintball marker the needle gets pressed down and the entire system becomes pressurized and is ready to be fired. Then when the gun is cocked and the trigger is pulled the bolt is pushed forward, accelerated by the force of the C02 acting behind it and pushes the paintball out. Then the bolt comes back into the read position and the C02 is no longer flowing and is again pushing against the bolt.
There are some problems with this system however. One of the major ones is called snowing, where liquid C02 actually gets into the paintball marker, this is not good for multiple reasons, first of all having the liquid C02 on the moving parts inside a marker is not good for it, since many of the parts inside are rubber or plastic. The second problem with this is since the gas is in liquid form it is not expanding as fast and there for is not pushing the paintballs as effectively. This causes a white snow like substance to come out of the barrel of the marker. There are several way that this problem is dealt with, some markers have the guns stored in a vertical position to keep the liquid in the bottom of the tanks. Other markers employ gas lines or expansion chambers, these are basically just tubes or cylinders that run from the tank to the marker and give the C02 a chance to turn from a liquid to a gas.