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How Do I Put Air in My Water Tank?
If you mean a pressure tank connected to a water pump, you usually add air through the small air valve on the tank. It looks like the valve on a car tire.
But first, make sure you actually have a pressure tank designed to hold compressed air. Do not pump air into a normal rainwater storage tank, rain barrel, IBC tote, or atmospheric cistern. Those tanks are normally vented and are not designed to be pressurized.
For a bladder or diaphragm pressure tank, the basic process is:
- Turn off power to the pump.
- Drain all water pressure from the plumbing.
- Check the tank's air pressure with a tire pressure gauge.
- Add or release air through the tank's air valve.
- Set the pressure according to the tank and pump manufacturer's instructions.
- Close the drain or faucet and restart the pump.
A common setup uses a tank air pressure about 2 psi below the pump's cut-in pressure, but you should confirm the correct setting for your tank and pressure switch before adjusting it.
First, Identify What Kind of Tank You Have
Not every water tank should have compressed air added to it.
Bladder or diaphragm pressure tank
This is common on wells, rainwater pump systems, cabins, and household water systems.
Inside the tank, a rubber bladder or diaphragm separates the water from a pocket of compressed air. That air helps push water out of the tank between pump cycles.
These tanks usually have a Schrader valve, which looks like a tire valve.
You can normally check and adjust the air pressure through this valve.
Older non-bladder pressure tank
Some older pressure tanks do not have a bladder. Water and air share the same tank.
These systems may use an air-volume control or another method to maintain the correct air level. Adding air with a compressor without understanding the system can cause poor operation or excessive pressure.
If you have this type of tank, follow its manufacturer's instructions or have a pump professional inspect it.
Rainwater storage tank, rain barrel, IBC tote, or cistern
These tanks normally store water at atmospheric pressure.
They need a vent so air can enter as water leaves and escape as water enters.
Do not try to pressurize one with an air compressor. A storage tank that is not designed as a pressure vessel can deform, leak, or fail.
If your goal is stronger water pressure from a rainwater storage tank, you normally need a suitable pump and possibly a pressure tank rather than compressed air inside the storage tank itself.
Why a Pressure Tank Needs Air
Water does not compress much. Air does.
A pressure tank uses compressed air like a spring. When the pump fills the tank with water, the water compresses the air pocket. When you open a faucet or irrigation valve, that compressed air pushes water out.
This lets you use some water without starting the pump every time.
Correct air pressure can help:
- reduce rapid pump cycling,
- provide more usable water between pump starts,
- keep water pressure more stable,
- reduce unnecessary wear on the pump.
Too little or too much air can make the system work poorly.
How to Add Air to a Bladder Pressure Tank
1. Find the pump pressure settings
Before changing the tank pressure, determine your pump's cut-in pressure.
Cut-in pressure is the pressure at which the pressure switch turns the pump on.
For example, a pressure system might be designed around a particular cut-in and cut-out range. Do not assume your system uses the same settings as another home.
Look at the pressure switch, tank documentation, pump documentation, or system records.
2. Turn off electrical power to the pump
Switch off the pump at its proper disconnect or circuit breaker.
Do not work around exposed electrical wiring, wet electrical equipment, or damaged controls. Have a qualified professional handle electrical problems.
3. Drain the water pressure
Open a faucet, hose bib, or suitable drain downstream of the pressure tank.
Let the water run until the pressure gauge reaches zero and water stops flowing.
This step matters because you need to measure the tank's air precharge, not the pressure created by water pushing against the bladder.
The tank should normally be empty of water when checking precharge.
4. Find the air valve
Look for a small Schrader valve on the pressure tank. It may be near the top of the tank and may have a plastic cap over it.
Remove the cap.
5. Check the air pressure
Use a reliable tire pressure gauge on the valve.
Compare the reading with the pressure required for your tank and pump system.
Many bladder-type systems call for a precharge approximately 2 psi below the pump's cut-in pressure, measured with the tank drained and pump power off. Treat that as a common arrangement, not a universal setting.
Always use the specification for your particular tank and control system.
6. Add air slowly
If the pressure is too low, add air through the Schrader valve using a hand pump or suitable air source.
Add a little at a time.
With setting water-tank air pressure, you can verify equipment ratings required for continuous service.
Check the pressure after each adjustment. Avoid rapidly filling the tank from a high-pressure compressor.
If you add too much air, press the valve briefly to release some.
Never exceed the tank manufacturer's allowable pressure.
7. Restore the system
Once the precharge is correct:
- Remove the pressure gauge.
- Replace the air-valve cap.
- Close the faucet or drain you opened.
- Restore power to the pump.
- Let the system build pressure.
- Watch the pressure gauge as the pump starts and stops.
Check the tank, fittings, pressure switch, and nearby plumbing for leaks or unusual behavior.
Why You Must Drain the Tank Before Checking Air Pressure
Checking the valve while the system is still full of pressurized water can give you a misleading reading.
The water is pushing against the bladder, which also raises pressure on the air side.
To check the true precharge, the pump should be off and the water side should have no pressure.
This is one of the most common mistakes when adjusting a pressure tank.
What If Water Comes Out of the Air Valve?
Water coming from the Schrader valve on a bladder or diaphragm pressure tank is usually a warning sign.
It can mean the bladder or diaphragm has failed and water has entered the air side of the tank.
Adding more air is unlikely to solve the underlying problem.
A failed tank may also cause:
- very frequent pump starts,
- sharp pressure changes,
- little usable water between pump cycles,
- a tank that feels unusually full or heavy.
Have the tank inspected and replaced if necessary.
What If the Tank Keeps Losing Air?
A healthy bladder pressure tank should not need frequent air additions.
If the precharge keeps dropping, possible causes include:
- a leaking Schrader valve,
- a damaged bladder or diaphragm,
- a leak around the valve fitting,
- incorrect pressure settings,
- a problem elsewhere in the pump system.
You can check the air valve for obvious leakage, but repeated pressure loss deserves further inspection.
Continually adding air may hide a tank failure rather than fix it.
Signs the Air Pressure May Be Wrong
Air pressure is worth checking if your pump starts much more often than it used to.
Other clues include:
- the pump starts after using only a small amount of water,
- pressure rises and falls very quickly,
- water flow pulses noticeably,
- the pressure tank seems to hold very little usable water,
- the pump repeatedly switches on and off.
This rapid starting and stopping is often called short cycling.
Incorrect tank precharge can cause short cycling, but it is not the only possible cause. A failed bladder, clogged plumbing, incorrect pressure-switch settings, leaks, pump problems, or an undersized tank can produce similar symptoms.
Rainwater Tanks Need a Different Approach
A typical rainwater harvesting system may look like this:
roof → debris screening → storage tank → pump → pressure tank → plumbing or irrigation
The large storage tank holds the rainwater. It normally stays vented.
The smaller pressure tank is installed on the pressurized side of the pump. That is the tank containing the compressed air pocket.
If water barely flows from your rainwater tank, adding air to the storage tank is not the answer.
Instead, check whether the system needs:
- a pump,
- a correctly sized pressure tank,
- clean strainers and filters,
- proper pipe size,
- enough pump flow and pressure,
- correctly adjusted pump controls.
If you are relying only on gravity, pressure depends largely on head height. Head height is the vertical distance between the water surface and the point where you use the water. A storage tank only a few feet above a garden hose will produce much less pressure than a pumped system.
When to Stop and Call a Professional
Consider having a pump or plumbing professional inspect the system if:
- you cannot identify the tank type,
- water comes from the air valve,
- the tank will not hold its precharge,
- the pump short-cycles after the pressure is corrected,
- the pressure switch has exposed or damaged wiring,
- the pressure gauge appears unreliable,
- system pressure exceeds the tank's specifications,
- you are unsure whether the tank is safe to pressurize.
Never modify, weld, drill, or attempt to repair a pressurized tank while it contains pressure.
Frequently Asked Questions
Can I put air in a water pressure tank with a bicycle pump?
Yes, a bicycle or hand pump can often be used to adjust the precharge of a bladder pressure tank. Turn off the water pump and drain the water pressure first. Set the tank according to its manufacturer's instructions.
How much air should I put in my pressure tank?
Use the precharge specified for your pressure tank and pump controls. A common arrangement is about 2 psi below the pump's cut-in pressure, measured with the pump off and the water side fully depressurized. Do not assume this setting applies to every system.
Can I check my pressure tank without draining it?
You can get a pressure reading, but it may not tell you the true tank precharge. For an accurate precharge check, turn off the pump and relieve the water pressure according to the tank manufacturer's instructions.
Why does my pump keep turning on and off?
This is called short cycling. Low tank precharge can cause it, but so can a failed bladder, incorrect pressure-switch settings, leaks, restrictions, pump problems, or an undersized pressure tank.
What happens if there is too much air in the pressure tank?
Too much precharge can reduce the amount of water the tank can accept and may cause poor pump operation. Adjust it to the specification for the tank and pressure-control system rather than adding extra air for more pressure.
Should I put compressed air in my rainwater storage tank?
No. Normal rain barrels, IBC totes, cisterns, and other atmospheric rainwater tanks should remain vented unless they are specifically designed and rated as pressure vessels. Use a pump and suitable pressure tank if you need pressurized water.
Why is water coming from the air valve on my pressure tank?
On a bladder or diaphragm tank, water at the air valve often means the internal bladder or diaphragm has failed. Adding more air will not normally correct that problem, and the tank should be inspected.
