Pressure Tank

Overview

A pressure tank stores water under pressure so a well or booster pump does not have to start every time someone opens a tap. Without it, a pump would short-cycle on and off with each small draw, wearing out quickly. The tank holds a reserve of water against a cushion of compressed air; that air pushes the water back out into the house between pump runs, smoothing pressure and letting the pump rest. The bladder design keeps the air and water apart so the air charge cannot dissolve away over time, which was the weakness of older air-over-water tanks.

The Tank Shell is the steel vessel that contains everything. A Bladder divides it into a wet side and a dry side. The Air Valve sets the Air Cushion, the System Connection ties the wet side into the plumbing, and the Wet-Side Liner and Base Ring protect and support the tank.

How it works

The dry side of the tank is pre-charged with air through the Schrader Valve valve, typically two psi below the pump's cut-in setting. As the pump runs, water enters through the System Connection and stretches the Butyl Diaphragm, compressing the Air Cushion behind it. When the pressure reaches the cut-out setting the pump stops, leaving the tank charged. When a fixture is opened, the compressed air pushes the diaphragm back, forcing stored water out into the system until the pressure falls to cut-in and the pump restarts. The usable volume between those two points is the drawdown, and it is what keeps the pump from cycling on every cup of water.

The Check Valve in the inlet keeps stored water from bleeding back toward the pump, and the Bladder keeps the air charge captive so it does not become waterlogged. Over years the diaphragm can fatigue or the air charge can leak through the Schrader Valve valve; a tank that has lost its pre-charge lets the pump short-cycle again, which is the usual sign it needs recharging or replacement.