Most well pumps that get replaced did not need replacing. The tank next to them failed, the pump started and stopped every few seconds trying to compensate, and the motor died of exhaustion.
A pressure tank costs a fraction of a pump and it is the part that decides how long the pump lives.
How Does a Well Pressure Tank Work?
A well pressure tank holds a cushion of compressed air above a rubber bladder full of water. The pump fills the bladder, the air compresses, and that stored pressure feeds the house between cycles, so the pump can stay off while a tap runs.
Key Takeaways
- The tank stores pressure, it does not create it.
- Set air pressure 2 psi below the pump’s cut-in, tank drained.
- Rapid cycling is the tank talking, not the pump.
- Size for one minute of pump run time, minimum.
- A failed tank kills pumps faster than anything else.
Setting the Air Charge
| Pressure switch | Cut-in | Air charge |
|---|---|---|
| 20/40 | 20 psi | 18 psi |
| 30/50 | 30 psi | 28 psi |
| 40/60 | 40 psi | 38 psi |
The measurement only counts with the power off and the tank drained of water. Checking the Schrader valve with water still inside reads the water pressure back at you, which is why so many tanks get declared healthy while waterlogged. The switch settings that pair with these are covered in our pressure switch guide.
Signs the Tank Has Failed
- Pump cycling every few seconds while a tap runs.
- Water from the air valve on top, which means a torn bladder.
- Uniform weight when you rock it, instead of bottom-heavy.
- Pressure spiking and dropping at the fixtures.
- A tank that sweats along its whole height.
The rocking test settles most cases in ten seconds. A healthy tank is heavy at the base and light on top, because most of it is air, and a waterlogged one feels like a filled drum from end to end.
Why Short Cycling Destroys Pumps
Every start puts the motor through its highest current draw and the mechanical seal through a dry moment before the liquid film reforms. A pump designed for a hundred starts a day does not survive a thousand.
The seal usually reports the damage first, as covered in our pump mechanical seal guide, and on a submersible it takes the starting components with it, which we cover in the well pump control box guide.
Sizing and Replacing
Size the tank from the pump’s flow rate and the run time the motor needs, which for most residential pumps is one minute. Ten gallons per minute therefore calls for around ten gallons of drawdown, and drawdown is a much smaller number than the tank’s nominal capacity.
Replacement is straightforward plumbing, though the air charge has to be set before the tank sees water. Guidance for private well owners generally is published by the EPA. If pressure problems persist with a healthy tank, the pump itself may be the issue, which our guide to telling whether a well pump is bad walks through.
Frequently Asked Questions
How big of a pressure tank do I need for my well?
Pressure tank size follows the pump’s flow rate and the run time the motor needs, usually one minute. A pump delivering 10 gallons per minute therefore wants about 10 gallons of drawdown, which is roughly a 30 gallon tank. Drawdown is always a smaller number than the tank’s nominal capacity, so compare drawdown rather than the size printed on the side.
How do you know when a well pressure tank is bad?
You know a well pressure tank is bad when the pump cycles every few seconds while a tap runs, when water sprays from the air valve on top, or when rocking the tank shows it is heavy all the way up instead of bottom heavy. Pressure that spikes and collapses at the fixtures points the same way.
How long does a well pressure tank typically last?
A well pressure tank typically lasts somewhere between 5 and 15 years, with the bladder being the part that gives out rather than the shell. Tanks that are run at the wrong air charge fail at the short end of that range, because the bladder flexes further on every cycle than it was designed to.
Can I add air to my pressure tank without draining it?
You can add air to a pressure tank without draining it, but the gauge reading will be wrong, because with water inside you are measuring system pressure rather than the air charge. Setting the charge correctly means killing the power and draining the tank first, then pumping it to 2 psi below the pump’s cut-in setting.
Can I run my well pump without a pressure tank?
Running a well pump without a pressure tank is possible but it destroys the pump quickly, because every time a tap opens the pump starts and every time it closes the pump stops. The tank exists to absorb that demand so the motor runs in long cycles instead of hundreds of short ones.
Pressure Tanks at Ken’s Distributing
Ken’s Distributing supplies pressure tanks, switches and gauges alongside the Franklin Electric range and the Monarch water pump range.
Tell us the pump’s flow rate and the switch settings, and we will size the tank for a full minute of run time rather than to whatever fits the space.