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Well Pressure Tank: How It Works, Signs It's Failing and Replacement
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How a well pressure tank works
When the pump runs, it pushes water into the tank and squeezes the air inside, which puts the water under pressure. When the pressure reaches the stop setting (often 50 or 60 psi), the pressure switch shuts the pump off. As you use water, pressure falls. At the start setting (often 30 or 40 psi), the switch starts the pump again. Nebraska Extension gives these typical settings.
Washington's health department adds that the tank keeps pressure in a desired range, limits pump cycling (frequent starts and stops can damage equipment) and protects against water hammer.
Types of well pressure tanks
| Type | How it works | Care |
|---|---|---|
| Bladder or diaphragm tank | A rubber bladder holds the water, so air and water never touch. Most private systems have used this type since 1970. | Factory charge is around 20 psi. Most makers say to charge it about 2 psi below the pump-on pressure. |
| Galvanized steel tank with a wafer | A floating wafer separates air and water. | Must be recharged with air manually every 6 to 12 months. |
| Plain galvanized steel tank | Air and water touch, so water absorbs air. | Needs an air-volume control, or it can become waterlogged. Common on older systems. |
Sources: Nebraska Extension G2152, Washington State Department of Health.
Nebraska Extension notes that because a bladder tank has almost no water left at the pump-on pressure, bladder tanks may not suit low-yield wells unless an additional tank is used.
Signs your well pressure tank is failing
- The pump cycles on and off rapidly. Washington's health department and Nebraska Extension both link this to a waterlogged or low-air tank. WA says more than six starts an hour points to a waterlogged tank.
- The pump runs only a few seconds and shuts off. Nebraska Extension says pressure is building up too fast because there is not enough air in the tank.
- Water comes out of the air valve when the center pin is pressed (Washington).
- The tank sounds or feels different. Washington says a waterlogged tank sounds different when tapped, and gently tipping the tank can show it is heavy with water. Nebraska says to tap the side to check whether it is empty when the pressure is at zero.
- Stale, rusty water at the tap, which Washington says can come from corrosion inside the tank. Rusty water can also come from iron in the well; see our iron guide.
- Air pressure drops again within a week after a licensed pro recharges it. Nebraska Extension says the tank may need to be replaced.
Why it matters: Washington says too much cycling can shorten the life of the well pump motor. WA also lists higher energy costs, inefficiency and equipment failure for a waterlogged tank.
Sizing a replacement
- Match or beat the old tank's usable storage. Nebraska Extension says a new tank should have a storage volume equal to or greater than the old one, and that this means usable storage, not total tank volume. Choose the next larger size if your household's water use has grown.
- Nebraska's rule of thumb: multiply the pump flow rate (a typical home pump gives 5 to 10 gallons per minute) by four to pick a diaphragm or bladder tank size. Its example: a 9-gpm pump calls for a 36-gallon tank. Ask your pump pro to confirm.
| Bladder tank total size (gal) | Usable water at 20 to 40 psi (gal) | Usable water at 30 to 50 psi (gal) | Usable water at 40 to 60 psi (gal) |
|---|---|---|---|
| 4.5 | 1.7 | 1.4 | 1.2 |
| 14 | 5.1 | 4.3 | 3.7 |
| 20 | 6.5 | 5.5 | 5 |
| 32 | 12 | 10 | 8.5 |
| 45 | 18 | 15 | 12 |
| 62 | 21 | 19 | 17 |
| 90 | 30 | 26 | 23 |
Source: Nebraska Extension G2153, Table I (from the Midwest Plan Service Private Water Systems Handbook). A tank holds much less usable water than its total size; Washington's health department says bladder tanks provide no actual useful water storage capacity.
What replacement costs
We did not find a replacement price from an extension service or government page, and the cost-estimate sites we saw were not independent, so we do not quote a price. Get written quotes from a licensed plumber or well contractor. Ask whether the quote includes the pressure gauge and fittings and whether they will test the pressure switch settings.
What to do
- Note what the pump does: how often it starts, how long it runs, what the pressure gauge reads.
- If the pump cycles rapidly, turn off the pump breaker if you cannot get a pro right away, to avoid wearing out the motor (a protective step we suggest).
- Call a licensed well contractor or plumber. See our well pump troubleshooting guide for other causes.
- After any work, ask the pro to confirm the air charge is set 2 psi below the pump start pressure and to check that the pump cuts in and out at the right pressures.
Not sure what's wrong with your water?
Our free checker matches what you see, smell or taste to the likely cause, the test to ask for and the type of treatment that fits.
Open the well water checkerCommon questions
What does a well pressure tank do?
Nebraska Extension says the pressure tank stores water and provides water under pressure when the pump is not running. It builds up a reserve so the pump starts and stops less often, which prolongs the life of the pump, and it provides a reserve for times of high demand.
How long does a well pressure tank last?
Nebraska Extension says a pressure tank will last about 10 years, although some have performed properly for 30 years. Washington's health department says a bladder pressure tank lasts 5 to 7 years on average. Use those as a range, not a promise.
What is a waterlogged pressure tank?
In a bladder tank, Washington's health department says the tank is waterlogged when the internal bladder fails and water fills the air space around it. Its advice is to replace waterlogged tanks, and notes it is often most cost-efficient to replace one.
What pressure should the tank be set to?
Nebraska Extension and Washington's health department both say the air pressure in an empty bladder tank should be 2 psi below the pump's start pressure. For example, with a 30 psi start pressure the drained tank should read 28 psi. The target is often printed inside the pressure switch cover.
Can I replace a well pressure tank myself?
Nebraska Extension says the maintenance these systems need should be performed by a licensed professional, and notes some manufacturers void the tank warranty if anyone other than a licensed professional removes the air valve cap. Washington's health department says to follow the manufacturer's instructions only if you have the technical ability to do so safely. Replacement means working with pressurized water and the pressure switch's electrical connection, so we suggest hiring a licensed plumber or well contractor.
Related guides
- Well pump not working: troubleshooting checklist
- What's wrong with my well water? (checker)
- Iron and orange stains in well water
- Well water testing
- Rotten-egg smell in well water
- University of Nebraska–Lincoln Extension (NebGuide G2152): Private Drinking Water Wells: The Distribution System (July 2012)
- University of Nebraska–Lincoln Extension (NebGuide G2153): Private Drinking Water Wells: Operation and Maintenance for Mechanical Components (June 2012)
- Washington State Department of Health: Troubleshooting Bladder Pressure Tanks (DOH 331-342, revised Sept. 2017; a Drinking Water Tech Tip)
- Washington State Department of Health: Hydropneumatic Tank Control Systems (DOH 331-380, revised 6/23/2023; a Drinking Water Tech Tip)