What is a Well Pressure Tank & How Does it Work?

Well pressure tanks are an essential component of a well system, along with the pressure switch and well pump.

If you’re buying a well pressure tank for a new well or replacing the pressure tank in an existing well, this guide is for you. We’ve outlined everything you need to know about well pressure tanks to help you confidently invest in the right type of tank for you.

❔ What is a Well Pressure Tank?

A well pressure tank is a large tank that contains compressed air (at the top of the tank) and water (at the bottom of the tank).

The purpose of the tank is to give you instant access to well water, without you having to manually switch the well pump on. It also reduces how often the pump needs to cycle on and off, extending the pump’s lifespan.

well water pressure tank

📖 How a Well Pressure Tank Works

We know now that well tanks contain compressed air. When you turn on a faucet or a water-using appliance, this compressed air exerts pressure on the water drawn from the well, sending it out of the tank and through your plumbing at a consistent rate.

Here’s the exact process that takes place in a well pressure tank:

  1. Water from the well is pumped into the bottom of the pressure tank.
  2. Water rises in the tank, which causes the air to become increasingly compressed.
  3. Once the air pressure reaches between 50 and 60 PSI, the well pump shuts off, and no more water enters the tank.
  4. When you switch on a faucet or a water-using appliance, the pressure in the tank forces water through your plumbing system.
  5. This continues until the air pressure drops to 30-40 PSI, and then well pump switches back on to replenish the water that has been used in your home.

✅ The Benefits of Well Water Pressure Tanks

There are several perks of installing a well water pressure tank downstream of your well pump:

Steady Supply of Water

One of the main reasons why people install a well water pressure tank is to deliver a steady supply of water around their home.

A pressure tank ensures your water pressure remains consistent, so that there is always water available to be delivered around your home.

well pressure tank in basement

Emergency Use

A pressure tank gives you peace of mind that you’ll always have access to a supply of drinking water in emergencies.

A pressure tank holds 20, 30, 50, 60 85, or 120 gallons of water, depending on the size of the tank you buy. So, if your well dries up, you’d have enough water in your pressure tank for at least two days of normal use.

Reduces Pump Wear

Without a pressure tank, your well water pump would have to switch on and off tens of times throughout the day.

A pressure tank stores water, extending the time between the pump turning on and off. This extends the life of the pump.

📝 Types of Well Pressure Tanks

There are three common types of well pressure water tanks:

  • Diaphragm tanks. These tanks separate the air and water with a vinyl or rubber diaphragm. The diaphragm stretches upward as water flows into the tank, compressing the air above.
  • Bladder tanks. These tanks contain water in a balloon-like bladder. As water is pumped into the tank, the bladder expands, compressing the air.
  • Air-over-water tanks. These tanks don’t separate the air and water with a physical barrier. The problem with air-over-water tanks is that air dissolves into the water over time, requiring monitoring and more maintenance than bladder or diaphragm tanks.
Types of well pressure tanks illustration

🤔 How to Choose a Well Pressure Tank

To choose a well tank, you need to know certain information:

System Demand

System demand is how much water a well can deliver, measured in gallons per minute (GPM) and pounds per square inch gauge (PSIG). To work out the GPM you need from a well water system tank, total the number of fixtures in your home. So, if your home has 10 fixtures, you need a minimum flow rate of 10 GPM.

Pump Capacity

Your pump capacity is usually determined based on the required system demand. If you have an existing pump, find out its capacity before choosing a water tank.

Pressure tank gauge

Well Capacity

Finally, you should have documentation of your overall well capacity, usually measured in gallons per hour (GPH). If you don’t know your well capacity, you can measure the capacity by lowering your water level, then timing how long it takes for water to return to static water level.

With these three factors in mind, you can choose the suitable total volume for your tank. Most average homes will be fine with a tank with a holding volume of between 30 and 85 gallons.