Well pressure tank problems and replacement

The pressure tank is the reason your pump doesn't run every time someone washes their hands. Inside most modern tanks a rubber bladder or diaphragm separates water from a cushion of compressed air. The pump fills the tank against that air; when you open a tap, the air pushes water out until pressure drops low enough for the switch to call the pump again. When the air charge is wrong or the bladder fails, the pump starts and stops constantly, and that wears out pumps and switch contacts.

Signs the tank is the problem

• The pump clicks on and off every few seconds while a faucet is running.
• The pressure gauge swings fast between low and high.
• Air added to the tank leaks back out within days.

University of Nebraska Extension's well guide puts it simply: when the pump runs only a few seconds and shuts off, pressure is building too quickly because there isn't enough air in the tank.

How the air charge is checked

The correct air pressure is read with the tank empty. Nebraska Extension describes the routine: power to the pump goes off, faucets run until the gauge reads zero, the tank gets tapped to confirm it's actually empty, and then an ordinary tire gauge on the valve at the top reads the air charge. It should sit 2 psi below the pump's start (cut-in) pressure, so a system that starts at 40 psi wants 38 psi of air. If it's low, air gets added with a compressor. If the charge leaks down again within a week, or water was left in the "empty" tank, the tank usually needs replacing.

Some tank makers void their warranty if someone other than a licensed professional removes the valve cap, so check before you start pumping air into it yourself.

Sizing the replacement

Tanks are sold by total volume, but what matters is drawdown: how many gallons the tank actually delivers between cut-out and cut-in. A replacement should give at least as much drawdown as the old one, and more if the household has grown. Nebraska Extension reprints this table from the MidWest Plan Service handbook for bladder and diaphragm tanks:

Notice how much drawdown shrinks as the pressure range goes up. Raising the switch setting for better shower pressure without a bigger tank means more pump starts.

On a low-yield well, which is common in parts of Union and Anderson counties according to state driller records, a larger tank can also help cover short bursts of demand while the well recovers. See the county table.

How long tanks last

Nebraska Extension puts typical pressure tank life around ten years, though some run thirty. If yours is original to a house built a couple of decades ago and the pump has started cycling, the tank is the first suspect.

Who should replace it

The tank, switch and the piping around them are part of the well system, and TDEC requires a license from anyone who installs or repairs well pumps and their equipment. The installer will set the new tank's air charge to match the switch, check the switch contacts, and make sure the pump isn't already damaged from cycling. If the pump has been short-cycling for months, ask them to look at it while they're there; see well pump repair.

Good questions

What pressure should my well tank be set to?

With the tank empty, 2 psi below the pump's cut-in pressure. For a 30/50 switch that's 28 psi; for 40/60 it's 38 psi. The switch settings are usually printed inside the switch cover.

Can a waterlogged tank ruin my pump?

It can shorten its life. Every start is hard on the motor and the switch contacts, and a waterlogged tank turns one start into dozens.

Is a bigger pressure tank always better?

More drawdown means fewer pump starts, so bigger is generally kinder to the pump. Space, cost and the switch setting all play in; the installer can size it to your household.