Quick answer
A well pressure tank is a sealed steel tank, usually holding a rubber bladder or diaphragm with compressed air around it, that stores well water under pressure so taps get water while the pump is off and the pump starts and stops less often.
A pressure switch starts the pump at a low setting and stops it at a high one. The water delivered between those two points is the drawdown, and it is much smaller than the tank’s size on the label.
Quick facts
The key facts about Well Pressure Tank, with sources:
Key takeaways
- The tank uses squeezed air to push water out, so you get pressure without the pump running.
- Drawdown, the water between pump starts, is the number that matters, and it is a fraction of the tank size.
- The air pre-charge should sit about 2 psi below the pump cut-in setting.
- A pump that clicks on and off every few seconds usually means the tank has lost its air.
- Tanks are pressure vessels; a corroded or damaged one should be replaced, not re-pressurized.
How a well pressure tank stores water under air pressure
Water cannot be squeezed into a smaller space, but air can. Nebraska Extension explains that when water is pumped into a tank holding air, the air compresses and puts the water under pressure, and the more it is compressed, the higher the pressure 1.
Open a tap and that squeezed air pushes water out until the pressure falls to the pump’s start point.
Nebraska Extension lists three purposes: store water and supply it under pressure while the pump is off, build a reserve so the pump starts and stops less often, prolonging its life, and supply extra water at times of high demand 1.
Most homes now have bladder or diaphragm tanks, where a rubber membrane keeps the air and water apart, as the cutaway below shows 2. Older systems used plain galvanized steel tanks where air and water touch 1.
- Air valveTire-style valve on top, used to check pre-charge 2
- Compressed airSqueezed as water enters; pushes water out when taps open 1
- Rubber diaphragm or bladderKeeps air and water apart, so no air injection is needed 1
- Stored waterThe drawdown your taps use between pump starts 1
- System connectionSingle inlet and outlet pipe to the tank tee 1
Tank size is not water stored
A tank labeled 32 gallons does not give you 32 gallons between pump starts. Nebraska Extension’s table shows a 32-gallon bladder tank delivering 8.5 to 12 gallons, depending on the switch setting 1. Compare drawdown, not total volume.
How one pressure cycle runs, from cut-in to cut-out
Using a 30–50 psi switch, the example setting Clemson Extension gives 3.
- Pump off, tank full: Air is compressed and the gauge reads about 50 psi.
- Water used: The bladder empties as air pushes water to the taps; pressure falls.
- Cut-in: At 30 psi the pressure switch starts the pump 3.
- Refill: The pump fills the bladder and re-compresses the air.
- Cut-out: At 50 psi the switch stops the pump 3. In a bladder tank, almost no water is left in the bladder at the cut-in point 1.
Which tank types exist and how each keeps its air
| Type | How it keeps air | Notes |
|---|---|---|
| Galvanized steel (plain) | Air and water touch; needs an air volume control | Most common until 1970; can waterlog or air-bind 1 |
| Galvanized with floating wafer | A wafer separates air and water | Almost doubles usable storage; still needs manual recharge 1 |
| Diaphragm tank | A fixed rubber diaphragm | No air injection needed 1 |
| Bladder tank | Water inside a butyl or PVC bladder | Single inlet/outlet pipe; can go anywhere in the system 1 |
| Small tank with a VFD pump | Pre-charged, often 1–2 gallons | Constant-pressure systems; the drive varies pump speed 1 |
Example: sizing a tank from pump flow, then checking drawdown
Nebraska Extension sizes a bladder or diaphragm tank at about four times the pump’s flow in gallons per minute, and a plain galvanized tank at about ten times 1. Applied to four common pump sizes, the example works out like this:
| Pump flow | Bladder tank (× 4) | Galvanized tank (× 10) |
|---|---|---|
| 5 gpm | About 20 gallons | About 50 gallons |
| 7 gpm | About 28 gallons | About 70 gallons |
| 9 gpm | About 36 gallons | About 90 gallons |
| 12 gpm | About 48 gallons | About 120 gallons |
The size is only the start, because the switch range decides how much of that tank you can use.
The chart uses the MidWest Plan Service table that Nebraska reprints: the same 32-gallon bladder tank gives less water per cycle as the range rises, so raising pressure for stronger showers makes the pump cycle more often.
The same table rates that 32-gallon bladder tank equal to an 82-gallon galvanized one 1.
Where the tank and its parts are
The tank usually sits in a basement, utility room or well house where the water line from the well enters.
Around it you will find the pressure switch, a pressure gauge, and often a tank tee with a drain valve.
Nebraska Extension notes that a bladder tank can be placed anywhere in the system, and that long runs over 500 feet sometimes get a second tank near the far end 1.
An older galvanized tank usually sits within 4 feet of a jet pump 1.
The air valve, like a tire valve, is on top of the tank. The pre-charge setting for your system is often printed on the pressure switch lid or just inside its case 2.
One maker says to install its tank as close as possible to the pressure switch, mount it vertically, and keep it out of freezing temperatures and temperatures above 100°F 4.
What a well-sized tank does
Benefits
What a pressure tank cannot fix
A tank does not make a weak well stronger. If the well yields little water, Nebraska Extension notes that bladder tanks may not suit it without an additional tank, because almost no water is left in the bladder at the cut-in point 1.
A tank also cannot raise pressure above what the switch and pump deliver; fixtures need at least 10 psi, and water treatment units, softeners, washers and dishwashers need at least 30 psi 1.
And a bigger tank will not cure low flow caused by clogged pipes, a failing pump or a stuck check valve.
What changes the cost of replacing a pressure tank
We do not print prices, because fair numbers need dated local quotes.
Replacement cost depends mostly on tank size and type, whether the pressure switch, gauge and tank tee are replaced at the same time, and whether the tank must fit a tight space.
Nebraska Extension says a replacement tank should have a storage volume (drawdown) equal to or greater than the old one, and the next size up if household demand has grown 2.
Lifespan: Nebraska Extension says a pressure tank will last about 10 years, although some have worked properly for 30 2. Water quality matters; one maker says to test for corrosive elements, acidity and total solids before installing 4. Our plumbing cost guide explains other price drivers.
How a new tank is set up
A summary of Nebraska Extension’s guidance 21 and one maker’s manual 4. Nebraska recommends a licensed professional; electrical work on the pump circuit is not homeowner work.
- Size the tank: about four times the pump’s gallons per minute for a bladder or diaphragm tank 1.
- Before filling, check the factory pre-charge; one maker ships at 38 psig, plus or minus 10% 4. Nebraska Extension describes bladder tanks charged around 20 psi at the factory 1.
- Set the pre-charge 2 psi below the pump cut-in setting, for example 28 psi for a 30 psi cut-in 14.
- Mount the tank vertically on a level base near the pressure switch, protected from freezing 4.
- Install a relief valve sized for the pump, as the maker requires 4.
- Restore power, let the system cycle and check the cut-in and cut-out readings on the gauge.
How a professional checks the air charge
Nebraska Extension describes this check as work for a licensed professional 2.
- Turn off power to the pump and open faucets until the gauge reads zero 2.
- Tap the tank; if water remains, the bladder may have failed 2.
- Measure air at the top valve with a tire gauge; it should be 2 psi below cut-in 2.
- Add air only if the tank is sound; re-check a week later, since a falling reading may mean replacement 2.
- Watch the gauge in normal use; Clemson suggests replacing a gauge that does not move or reads far out of range 3.
Warning signs and when to call
- The pump runs a few seconds and shuts off, over and over: not enough air in the tank 2.
- Pressure swings hard at the faucet during use.
- Water comes out of the air valve when pressed: a torn bladder.
- Rust, sweating or a leak on the tank shell 4.
- The pump runs nonstop or pressure drops with taps off: a check valve or leak problem 2.
A pressure tank can burst
One maker warns that adding pressure to a corroded or damaged tank, or one that has lost air, can cause rupture or explosion and serious injury, and says not to adjust pre-charge in those cases 4.
Turn off pump power before anyone works on the tank. Nebraska Extension says homeowners should not adjust the pressure switch, which is wired to live power 2.
Short cycling can burn out a well pump, so call a well or water system professional soon. For no water at all, see plumbing emergencies.
Who licenses tank work and what makers require
Licensing: many states license well and pump installers. EPA advises hiring contractors who are bonded, insured and, where the state requires it, licensed and certified 5. In Nebraska, Extension guidance points owners to a state-licensed professional for pump and tank work 2.
Maker requirements: one maker’s tanks are air tested to 150 psig, the line’s maximum working pressure, and must have a relief valve set below that or the local code limit, whichever is less 4.
Water testing: EPA advises testing private wells every year for total coliform bacteria, nitrates, total dissolved solids and pH 5.
Plumbing codes govern the house piping beyond the tank, and state well codes vary. Rules checked 2026-10-13.
How a pressure tank differs from an expansion tank and switch
| Part | Job | Key difference |
|---|---|---|
| Well pressure tank | Stores pressurized water; cuts pump starts 1 | Sized by drawdown |
| Expansion tank | Absorbs heated water’s expansion | Small; on the water heater side |
| Pressure switch | Starts and stops the pump 1 | The control, not storage |
| Well pump | Lifts water from the well 1 | Supplies the tank |
| VFD controller | Varies pump speed for constant pressure 1 | Uses a much smaller tank |
Pressure tank myths that shorten pump life
- Myth A 40-gallon tank holds 40 gallons of usable water.
- Reality Usable drawdown is a fraction of total volume 1.
- Myth Higher pressure settings are free.
- Reality Higher ranges shrink drawdown and add pump cycles 1.
- Myth You can always add air to fix short cycling.
- Reality Not on a corroded or damaged tank 4.
- Myth Tanks last as long as the house.
- Reality About 10 years is typical, per Nebraska Extension 2.
Freezing climates and well regions
Private wells, and so pressure tanks, are most common in rural areas.
Climate is the local variable: one maker says its tanks must not be exposed to freezing temperatures 4, so tanks in well houses or unheated spaces need heat or insulation in cold regions.
Licensing rules for who may service the system also vary by state 5. Ask your state well-contractor licensing agency or local health department.
Recharge, replace or resize?
If the tank is sound and only low on air, a professional can recharge it. If it is waterlogged, rusted or leaking, replace it with at least the same drawdown. If the household now uses more water, step up a size.
Next step: note your pressure switch range and the tank model, then watch the gauge through one full pump cycle.
Size from the pump, check with the table
Nebraska Extension’s rule: multiply pump flow by four for a bladder tank, so a 9 gpm pump calls for about a 36-gallon tank 1. Then check its drawdown at your switch range in the maker’s table.
Questions about Well Pressure Tank
Should a well pressure tank be full of water?
No. A working bladder or diaphragm tank holds only its drawdown, a fraction of its size, with a cushion of compressed air above.
Nebraska Extension’s check is to switch off the pump, open taps until the gauge reads zero, and tap the tank: if it still sounds full of water, the bladder may have failed.
A tank that feels heavy and makes the pump short-cycle is usually waterlogged.
What should the air pressure be in a well pressure tank?
About 2 psi below the pump’s cut-in pressure, measured with the tank empty of water and the pump off. For a 30–50 psi switch, that means about 28 psi. The setting for your system is often printed on the pressure switch lid.
How do I know if my pressure tank is bad?
The classic sign is a pump that starts and stops every few seconds, which means the tank has lost its air. Other signs are water coming out of the air valve, big pressure swings at taps, and rust or leaks on the tank shell.
What size pressure tank do I need for my well?
Nebraska Extension suggests about four times the pump’s flow in gallons per minute for a bladder or diaphragm tank, so a 9 gpm pump calls for about a 36-gallon tank. A galvanized tank is sized at ten times. Confirm drawdown at your switch range.
What is drawdown on a pressure tank?
Drawdown is the usable water the tank delivers between the pump shutting off and starting again. It is much smaller than the tank size. A 32-gallon bladder tank gives about 10 gallons at a 30–50 psi setting, per Nebraska Extension’s table.
How long does a well pressure tank last?
Nebraska Extension says about 10 years, although some have worked properly for 30. Water chemistry, how often the pump cycles and whether the air charge is kept right all affect life. Check the maker’s warranty for your model.
What is a waterlogged pressure tank?
It is a tank that has lost its air cushion, so it fills almost completely with water. With no air to compress, pressure jumps the moment the pump runs, and the pump short-cycles. In bladder tanks, it often means the bladder has torn.
Can I add air to my well pressure tank myself?
Nebraska Extension describes this as a job for a licensed professional, and one maker warns that adding air to a corroded or damaged tank can cause it to rupture. The power must be off and the tank drained of water before the air is checked.
Does a constant-pressure well system need a pressure tank?
Yes, but a small one. Systems with a variable frequency drive change pump speed to hold pressure, and Nebraska Extension notes they typically use a small pre-charged tank, usually 1 to 2 gallons, to even out pressure changes.
Sources
- Nebraska Extension, Private Drinking Water Wells: Water Distribution System Components (G2152), incl. MidWest Plan Service Table I, retrieved .
- Nebraska Extension, Private Drinking Water Wells: Operation and Maintenance of Mechanical Components (G2153), retrieved .
- Clemson Cooperative Extension, Residential Drinking Water Well: Well Components (1st in Series), retrieved .
- AMTROL, Well-X-Trol Installation and Operation Instructions (WX-201 manual, distributor copy), retrieved .
- U.S. EPA, Protect Your Home’s Water (private wells), retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: How the tank works, tank types, drawdown table, sizing multipliers, minimum fixture pressures and VFD tanks from Nebraska Extension G2152; air-charge check, short-cycle symptom, lifespan and replacement sizing from G2153; switch settings from Clemson Extension.
Factory pre-charge, 150 psig rating, relief valve, placement and rupture warnings from one AMTROL manual (single maker, labeled). The factory pre-charge differs between AMTROL (38 psig) and Nebraska Extension (about 20 psi); both shown. Contractor and testing advice from EPA. No prices.
Suggest a correction. We fix errors and say what changed.