Co2

Are you talking CO2 or HPA?

CO2 tanks usually just have a pin-valve on them and rely on the constant evaporative expansion rate of approximately 850psi to run paintball guns. If you're using a CO2 tank meant for paintball, it'll output at between 800-850psi until the pressure in the tank itself drops below that level. From what I've always understood, since CO2 changes phase from gas to liquid at relatively low pressures, you can't go past 850psi on a CO2 tank.

With HPA, you have a regulator on the tank and potentially one on the gun as well. With HPA, there's no constant expansion/evaporative rate like there is for CO2, so you have to regulate the flow to achieve the desired output pressure. HPA tanks usually have either a high pressure output reg or low pressure output reg on the tank itself. High output regs usually run around 800-850psi while low pressure output regs run 400psi or lower.