What type of water system?

[Dodgeman]

Bill,
If you are speaking of a well water system for your home water supply, and not your hydronic heating system, the air pressure in your tank should be 80% of your nominal water pressure. This is with your pump shut off, and the water pressure at zero (faucets open) So if your pump pressure is 50psi, the air pressure should be at 35 to 40 psi.