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Types of Pressure Tanks

What Are Pressure Tanks Used For?

Pressure tanks are designed for use in multiple plumbing applications. The two most common are well pressure tanks and water heater expansion tanks. A water pressure tank for a well is designed to help maintain adequate pressure in your pipes without requiring your well pump to run nonstop. A water heater expansion tank is designed for use on modern plumbing systems.

How Does Tank Size Relate to Tank Pressure?

There’s a direct relationship between tank size and tank pressure. An easy rule to remember is that the higher the operating pressure needed, the larger the tank that’s required to maintain it.

How to Size a Well Pressure Tank and Understanding Your Options

Most pressure tank manufacturers will provide guidance around choosing the right-size pressure tank for your plumbing and which settings are best for operation. If you’re uncertain what size tank is best for your situation, contact a licensed professional.

When examining the manufacturer’s guidance on new pressure tanks and their pumps, you may come across some industry terminology, such as pump runtime and drawdown.

• Runtime is how long the pressure tank’s pump needs to run to maintain the desired pressure in the application. Although you may notice some variation, in general, pressure tank manufacturers recommend a runtime of less than a minute for a pump motor with 1 horsepower or less. For motors that have more than 1 horsepower, the runtime should be at least two minutes. However, you should always defer to the manufacturer’s guidance for your particular model.
• Drawdown is another important term to understand. This is the amount of pressure in the tank that’s released through the plumbing system. If this amount of pressure is calibrated correctly, the pump will have to run less frequently to maintain the correct pressure level, thereby ensuring optimum function, lowering energy costs and preserving the life span of the pump.

Types of Well Pressure Tanks and Their Functions

A pressure tank for a well pump serves several functions. The first is to ensure there’s sufficient water pressure in your plumbing system to operate a washing machine or dishwasher and for showering. Well pressure tanks also guarantee your well pump will operate for one minute or more during each cycle, as required by pump manufacturers, to keep the pump functioning properly.

A pressure tank also holds a supply of water between each pump cycle, which can cut down on the number of cycles needed per day to maintain water pressure. This can improve the lifespan of your pump. The main types of well pressure tanks are diaphragm pressure tanks, bladder pressure tanks, and air-over-water pressure tanks. Pressure tanks also have varying orientations — including horizontal pressure tanks and vertical pressure tanks — to accommodate different plumbing configurations.

A diaphragm pressure tank has a compressed air chamber and a water chamber. The two chambers are separated with a rubber diaphragm designed to rise with the water level, triggering the pump to shut off. Although diaphragm pressure tanks are known for their efficiency, they can malfunction if the diaphragm dislodges from the sides of the tank, causing a sudden decrease in water pressure. A tank’s diaphragm can also fold over itself, which can cause the pump to run constantly and burn out.

Like a diaphragm pressure tank, a bladder pressure tank also has two separate chambers: one for compressed air and one for water. The bladder part can be thought of as a self-contained balloon full of water that can contract and expand. This mechanism causes the tank sensor to turn on the pump. An advantage of bladder pressure tanks is that they typically last longer than diaphragm pressure tanks, since they don’t have a diaphragm that can fail.

Air-over-water pressure tanks have a simpler design than other types of pressure tanks and are typically found in older homes. This type of tank only has one chamber. Pressurized air and water aren’t separated. These older models tend to be less efficient and are much larger than more-modern tanks, so they take up more space.

Water heater expansion tanks, also known as thermal expansion tanks, are paired with water heaters on modern plumbing systems. Although water expands when it’s heated, water won’t compress like other substances. Because of this, a water heater tank can build up excess pressure as water rises in temperature.

In the past, most homes had open plumbing systems in which any pressurized water in the pipes would simply be forced back into the main water supply when pressure within the system became too great. Today, due to environmental regulations, home plumbing systems operate on a closed system. This means that there’s nowhere for water to escape if water pipes build up too much pressure, which can damage the plumbing. Water heater expansion tanks are designed to prevent such damage to the plumbing.

Bladder Tank vs. Pressure Tank

• Efficiency: Standard pressure tanks require a minimum amount of water to maintain the correct air pressure required for operation. As the water level lowers, the pressure inside the tank decreases. Bladder tanks, on the other hand, can maintain pressure regardless of the water level.
• Durability: Bladder tanks have a rubber barrier that ensures the water inside never touches metal, preventing corrosion. Pressure tanks have a metal interior and can sometimes rust.
• Maintenance: Pressure tanks must be regularly inspected and occasionally reset to prevent clogging. Bladder tanks don’t need regular resetting.