What is a pressure tank?

The tank stands wherever the well line enters, usually a basement, utility room, or well house: a blue or gray steel cylinder 15 to 26 inches across and 2 to 5 feet tall, plumbed through a tank tee that also carries the pressure switch, the gauge, a drain, and often a shutoff. Find two parts before you need them. The tire-style Schrader valve hides under a plastic cap on the very top, and the pressure switch is the small gray box on the tee, its spring and contacts under a snap-on cover. That switch carries line voltage, so kill the breaker before the cover comes off.

The tank protects the pump; storing water is incidental. Every start punishes a motor, and a healthy tank holds starts to a handful per hour with a run of 1 to 2 minutes each time. Once the bladder tears or the air charge bleeds away, the tank fills solid with water, the reserve disappears, and the pump snaps on and off every 5 to 20 seconds while a single faucet runs. That is short cycling, and it destroys motors, switches, and contacts quickly, sometimes within weeks. The tells: audible hammering as the pump kicks on and off, shower pressure pulsing strong and weak, the gauge needle swinging its full range in seconds, and a tank that feels uniformly cold and sounds solid when you rap it. Tanks last 8 to 15 years.

Check the air charge once a year with the pump breaker off and the tank drained through the lowest faucet or the drain valve. With no water inside, the reading at the Schrader valve belongs 2 psi below the pump's cut-in setting: 28 psi on a 30/50 switch, 38 psi on a 40/60. Add air in short bursts with a bicycle pump or compressor, and stop immediately if water sprays out of the valve, because that means a torn bladder and a finished tank (air charge intervals). Time the run and rest cycle on the same visit; anything under 60 seconds of run time deserves attention (waterlogged tank diagnosis). The pressure tank checklist covers the yearly pass, and tank lifespans set the replacement window.