What a pressure tank does and where it goes
A pressure tank stores water under pressure so your pump does not run every time you turn on a faucet. Without one, your pump kicks on and off constantly, wearing out faster and wasting energy. The tank sits between your well pump and the rest of your house plumbing, usually in a basement, crawl space, or utility room where it stays protected from freezing.
The tank itself is a metal or composite vessel divided into two chambers by a rubber bladder or diaphragm. One side holds water; the other holds compressed air. As water enters, it compresses the air, building pressure. When you open a tap, that stored pressure pushes water out without the pump running. Once pressure drops to a set point, the pump turns back on to refill the tank.
Tank size matters. A 20-gallon tank works for a small household with one or two bathrooms. A 40-gallon or 60-gallon tank handles larger homes or higher water demand. If you have a well system without a tank, or your current tank is waterlogged or rusted, installation is a straightforward project that takes a few hours and basic plumbing tools.
Key Takeaways
- A pressure tank must be installed between your pump and the main water line, with the pump inlet below the tank outlet to prevent backflow.
- You will need to drain your system, disconnect the old tank if one exists, and install check valves and isolation valves to protect the new tank.
- The tank's air charge must be set to 2 pounds per square inch (PSI) below your system's cut-in pressure before water enters it.
- Pressure switch settings typically range from 30/50 PSI to 40/60 PSI, meaning the pump turns on at the lower number and off at the higher one.
- After installation, you will need to test the system for leaks and adjust pressure settings to match your household demand.
Shut off power and drain the system
Before touching any plumbing, turn off power to your pump at the breaker. This prevents the pump from running while you work and protects you from sudden pressure release. Leave the breaker in the off position and do not turn it back on until you have finished all connections and filled the tank.
Next, open the lowest faucet in your house—usually a basement or outdoor spigot—and let water drain completely. If you have a drain valve on your current tank, open that too. This step is essential because you cannot safely disconnect pressurized lines. Wait until water stops flowing before moving forward.
Once the system is empty, open a faucet upstairs to break any remaining pressure and confirm the lines are truly drained. You should hear air hiss out, not water spray.
Disconnect the old tank and prepare the location
If you are replacing an existing tank, use two adjustable wrenches to loosen the union fittings that connect it to the pump outlet and the main water line. Hold the fitting body steady with one wrench while turning the nut with the other. Once loose, unscrew by hand and set the tank aside. Wipe the threads clean with a cloth.
For a new installation with no existing tank, you will be working with the pump outlet line directly. Either way, inspect the location where the tank will sit. It should be on level ground, away from direct sunlight and freezing temperatures. A basement corner or utility closet works well. Make sure you have at least 12 inches of clearance on all sides so you can access the air valve and drain plug later.
If the floor is uneven, place the tank on a concrete pad or wooden base to keep it stable and level. An unbalanced tank can develop leaks at the fittings over time.
Install check valves and isolation valves
Before connecting the tank, you must install a check valve on the pump outlet line. This one-way valve prevents water from flowing backward into the pump when pressure drops. Wrap the male threads with plumber's tape (also called thread seal tape or PTFE tape) by wrapping clockwise three to four times. Screw the check valve onto the pump outlet by hand first, then tighten with a wrench.
Next, install an isolation valve (a ball valve) on the line between the check valve and the tank. This lets you shut off water to the tank without stopping the whole system. Again, wrap the threads with plumber's tape and screw it on hand-tight, then wrench-tight.
Some installations also benefit from a pressure relief valve set 10 PSI above your system's cut-off pressure. This protects the tank if pressure builds too high. If your pump already has a relief valve, you may not need another one—check your pump manual. If you do install one, place it on a separate line with a drain that runs to a floor drain or outside.
Set the tank's air charge before filling
This step is critical and often skipped, which causes problems later. Every pressure tank comes with an air valve on top, similar to a car tire valve. Before any water enters the tank, you must charge it with compressed air to the correct pressure.
The correct air charge is 2 PSI below your system's cut-in pressure. If your pump is set to turn on at 30 PSI (a common setting), charge the tank to 28 PSI. If it is set to 40 PSI, charge to 38 PSI. You will need a tire pressure gauge and an air compressor or hand pump.
Remove the plastic cap from the air valve. Press the gauge onto the valve stem and read the current pressure. Most new tanks arrive with some air already in them, but it may be too high or too low. Use the air compressor to add air if needed, or press the valve stem to release air if the pressure is too high. Once the pressure matches your target, replace the cap and move on to connecting water lines.
Connect the tank to the pump and main line
Wrap plumber's tape around the male threads of the union fitting that connects the tank to the isolation valve. Screw it on by hand, then use two wrenches to tighten—one holding the fitting body and one turning the nut. Do not over-tighten; hand-tight plus a quarter turn is usually enough.
The tank outlet (the line going to your house) connects to the main water line. Again, wrap threads with tape and use two wrenches to tighten. Make sure the pump inlet is below the tank outlet. If the tank sits higher than the pump, water can siphon backward and damage the pump.
Once all connections are tight, open the isolation valve slowly. Water will begin to fill the tank. You may hear air hissing out of the air valve as water pushes the air bladder up. This is normal. Let the tank fill completely—it should take a few minutes.
Test for leaks and adjust pressure settings
With the tank full, turn the pump power back on at the breaker. The pump should run briefly and then stop once the tank reaches the cut-off pressure. Listen and watch for any water dripping from the fittings or the tank body. If you see drips, turn off the pump when ready and tighten the leaking connection with a wrench. Do not over-tighten—a quarter turn is often enough to stop a small leak.
Once the pump stops, open a faucet upstairs and let water run for 30 seconds. The pump should stay off, drawing from the tank's stored pressure. When the pressure drops to the cut-in point (usually 30 PSI), the pump should turn back on automatically. If it does not, check that the pressure switch is wired correctly and the breaker is fully on.
Check the pressure gauge on the tank or on the line near the pump. It should read between 30 and 60 PSI depending on your settings. If the pressure is too low or too high, you may need to adjust the pressure switch. This usually involves turning a nut on top of the switch—consult your pump manual for the exact procedure, as it varies by model.
Drain and maintenance going forward
Most pressure tanks have a drain plug at the bottom. Once a year, especially before winter, open this plug and let any sediment or water that has collected drain out. This keeps the tank healthy and prevents rust from forming inside.
Check the air pressure in the tank once a year as well, using the same tire gauge. If the pressure has dropped more than a few PSI, the bladder may be failing and the tank may need replacement. A failing bladder allows air and water to mix, which reduces the tank's ability to store pressure and causes the pump to cycle too often.
If you notice the pump running more frequently than it did before, or if water pressure drops suddenly, the tank may be waterlogged. Drain it completely, recharge the air side to the correct pressure, and refill. If the problem returns within a few weeks, the bladder is likely damaged and the tank should be replaced.
Frequently Asked Questions
What size pressure tank do I need?
A 20-gallon tank works for homes with one bathroom and low water demand. A 40-gallon tank suits most two- to three-bathroom homes. A 60-gallon or larger tank is better for homes with four or more bathrooms or high peak demand, such as multiple showers running at once. Larger tanks reduce how often the pump cycles, which extends pump life.
Can I install a pressure tank myself, or do I need a plumber?
If you are comfortable with basic plumbing—wrapping threads with tape, tightening fittings with wrenches, and reading a pressure gauge—you can install a tank yourself. The work is straightforward and takes a few hours. If you are unsure about any step, or if your pump has unusual plumbing, hiring a licensed plumber is worth the cost to avoid mistakes that could damage your pump or system.
What happens if I skip the air charge step?
If you fill the tank without charging the air side first, water will compress the air inside and the tank will become waterlogged. The pump will cycle on and off constantly, wearing out faster and wasting energy. You will also notice low water pressure and frequent pump noise. The fix is to drain the tank completely, charge it to the correct pressure, and refill—so it is better to do it right the first time.
Why is my pump running more often after I installed the tank?
The most common cause is incorrect air pressure in the tank. If the air charge is too low, the tank cannot store enough pressure and the pump cycles more often. Check the air pressure with a gauge and recharge if needed. Another cause is a leaking check valve, which allows water to drain back into the pump overnight. If the pump runs when ready after you turn it off, a leaking check valve is likely the problem and should be replaced.
Do I need a pressure relief valve?
Many well pumps already have a built-in relief valve, so a separate one may not be necessary. Check your pump manual. If your pump does not have one, or if your system pressure tends to run high, a relief valve set 10 PSI above your cut-off pressure adds a safety layer. It prevents the tank and pipes from being damaged by excessive pressure.