What Pressure Tanks Are For A pressure tank is a steel tank that has a bladder inside it. The top part of the tank is filled with air under pressure, and the bottom is where the water is stored. The air pressure in the top keeps the pressure up in the tank. This prevents the pressure pump from running every time a faucet is turned on.
Pressure tanks vary in size from under one gallon up to several hundred gallons.
This means that the pressure pump fills the tank up until the pressure is 50 psi. The pump does not come on again until the pressure drops below 30 psi. The high and low points can be set differently, but if too close, the pump will come on too often. Pump is off, reservoir is full, ready to provide draw down water under pressure Pump still off. Providing draw down water through pressure range.