I have a galvanized holding tank. There is very little water in the tank, so upon demand, the pump cycles on and off repeatedly. I drained the tank (only a couple of gallons) and turned the pump back on but the problem continues. I don't see an air valve anywhere on the tank. There is some kind of screw adjustment thing on the pressure gauge, but that doesn't seem to do anything. How do I get more water in the tank?

What is the pressure when the pump turns on and what is the pressure when the pump turns off?