[Paul Copioli]

Remember, you must connect the pressure relief valve when using the pump. This valve relieves pressure at around 120psi, no matter what! This is why it is legal to run your pump continuously.

Why pump up to 120 psi when you only use 60psi? That is a matter of "pressure volume". Let's say I have a cylinder that uses the exact volume of air that is in the tanks. If the pressure of the tank is only 60psi, then when I fire the cylinder once I expel all of the air in the tanks. If the pressure in the tanks is 120psi, then I have double the available air to use at 60psi. Air is compressible, which means as you increase the pressure the volume the same mass of air takes up gets smaller. Since the air tanks are a constant volume, when you increase the pressure then the amount of usable air increases. For this reason, you should try to maximize the pressure you have in the tanks.