Expansion Tanks Key Terms

Learn about expansion tanks

By Marjorie Gilbert

Expansion tanks are used in closed systems for heating water. They can be used in domestic applications as well as commercial ones. They contain a diaphragm. One half of the expansion tank is connected to the water system, the other to air.

Expansion tanks come in various forms, can be made from different kinds of materials, and are may be designed for many purposes. The keywords below can help you choose the expansion tank that will work best for your company.

Thermal expansion tanks

Thermal expansion tanks work well in domestic hot water systems. The thermal expansion tanks are designed to absorb the water when it expands as it heats. They are often lined to resist corrosion. If a check valve or a valve for reducing pressure is installed, an expansion control device should be installed.
Try: Amtrol has an informative site and a selection of thermal expansion tanks.

Hydronic expansion tanks

Hydronic expansion tanks have diaphragms made of butyl. Wear and tear is minimized because the diaphragm doesn't stretch as much as those made of other materials. Hydronic expansion tanks work well in larger hot water systems.
Try: Flexon Industries has an informative site and has hydronic expansion tanks.

Potable water expansion tank

Potable water expansion tanks are for water systems that contain consumable water. This is different from a closed water system, such as those used for radiant floors.
Try: Watts Water Technologies has a great site that thoroughly explains their potable water expansion tank.

Hydropneumatic tanks

Hydropnematic tanks are expansion tanks that can be used to be used as a booster tank, for a well, or for an irrigation system. These expansion tanks work well for large systems and have capacities of 10 to 4000 gallons.
Try: Wessels Company manufactures hydropneumatic tanks.

Steel expansion tank

In steel expansion tanks the air and water are not separated by a bladder. In this case the air acts similarly to a spring when it absorbs the heat that's generated by the water.
Try: High Performance HVAC has excellent information on its site concerning steel expansion tanks.

Expansion tanks for radiant systems

These expansion tanks have plastic liners, and are designed to be corrosion resistant. The working pressure for these expansion tanks is 100 psi, and can withstand temperatures of 200 degrees Fahrenheit.
Try: Pex Supply has expansion tanks as well as useful information.