Well Pressure Tanks
Pressure tanks for water well systems store a few gallons of water under air pressure, so the pump doesn't have to start every time you open a tap. When the tank works, you never think about it. When it fails, the pump short cycles, the pressure surges and drops, and the pump motor wears out early.
How a well tank works
Most modern tanks have a bladder or diaphragm that keeps the water apart from a cushion of compressed air. Amtrol explains that the pump fills the tank and squeezes that air, and when the set pressure is reached the pump control shuts the pump off. As you use water, pressure drops, and when it falls to the set point the pump restarts.
The air charge is the part people forget. Amtrol says to set the tank's pre-charge 2 psi below the pressure switch cut-in. Check it with the system drained, at the air valve on top of the tank. Our guide to well pressure tank air pressure walks through it.
Signs your tank is failing
Amtrol lists rapid pump cycling and low system pressure as the symptoms of a tank that needs replacing, and says a tank with low or no air may need to go. Boshart adds a few you can check yourself:
- The pressure switch clicks on and off in quick succession.
- The top of the tank feels cold or sweats.
- Knocking on the upper half doesn't sound hollow.
- The gauge needle jumps around, and the shower surges.
Boshart warns that a waterlogged tank will burn out your pump, so don't put this off. Start with pressure tank troubleshooting or, if the tank sounds solid, our page on a waterlogged pressure tank.
Replace, resize or recharge
- Your tank has lost its bladder or is rusting: how to replace a well pressure tank.
- You want a price first: well pressure tank replacement cost. HomeGuide puts most replacements at $800 to $1,500 installed.
- You're not sure the old tank was big enough: what size pressure tank do I need?
A bigger tank isn't always better, but it's rarely worse. Amtrol's point is simple: the larger the tank, the more water it stores and the less often the pump has to run. HomeGuide puts typical tank life at 10 to 15 years, shorter in hard water.
FAQ
Is a pressure tank on a well supposed to be full of water?
No. A bladder tank holds some water, but most of its volume is air. Boshart says pressure tanks are typically 70 to 75 percent air. A tank that's full of water is waterlogged.
How long do well pressure tanks last?
HomeGuide gives an average of 10 to 15 years. Hard water, a wrong air charge and short cycling all shorten that.
How often should a pressure tank kick on?
There's no fixed number, because it depends on how much water you use and the tank size. What you don't want is the pump starting every few seconds during a small draw like rinsing a glass. That's short cycling, and it means the tank isn't doing its job.
Do all wells have a pressure tank?
Almost every household well with a standard pump and pressure switch has one. Constant-pressure pump systems typically get by with a smaller tank, but they still have one.
All guides in this section
Sources
- AMTROLWell-X-Trol Homeowner Handout (opens in a new tab)
- AMTROLWell Systems FAQs (opens in a new tab)
- Boshart IndustriesHow can I tell if my pressure tank is waterlogged? (opens in a new tab)
- HomeGuideHow Much Does It Cost to Replace a Well Pressure Tank? (opens in a new tab)