Using Expansion Tanks to Prevent Hydraulic Expansion

One of the consequences of installing a backflow prevention assembly on any water system is that it becomes a closed system. This means that it is not open to the atmosphere. Similarly, a pressurized tank would be a closed system, since there is no means for the pressure to escape.

Causes of Increase in Pressure in a Water System

A common phenomenon, which results in increased pressure, is hydraulic expansion. This occurs when water in the pipes heats up due to environmental conditions such as a hot room, or it may be caused by a piece of water-using equipment that is generating heat. Regardless of what causes the water to heat up, when it does it expands and requires more volume. This is not a problem in an open system, where the water flows back through the meter into the distribution system. However, when the system is closed; the water doesn’t have anywhere to go. In these conditions the pressure can increase dramatically.

Preventing System Damages in due to Thermal Expansion

Installing Expansion Tanks -

This situation can be protected by the installation of an expansion tank. An expansion tank is attached to the water system and may be pressurized with air on one side of a diaphragm within the tank. When the water pressure increases due to thermal expansion, the tank begins to fill with water pressurizing the air on the other side of the diaphragm. Water is not compressible, so when the water begins to expand due to heat, it needs to go somewhere. Air on the other hand is compressible. So, the expanded water goes into one side of the tank compressing the air on the other side. This prevents any part of the system from giving way to the expanding water.

There are three main types of expansion tanks used:

• Plain Steel Tank: It’s open to that atmosphere. In atmospheric expansion tanks, the water and air in the tank are in direct contact. Smaller models of atmospheric tanks can cost less than other styles of expansion tanks due to their

• Bladder Style Tank. There is a rubber bladder that expands and contracts as fluid expands and contracts within the system bladder tank usually have a higher initial cost and have a lower maximum allowable temperature than plain steel tanks because of the material of the bladder.

• Diaphragm Tank: diaphragm that separates the fluid in the top of the tank and the air in the bottom of the tank. Unlike bladder tanks, diaphragm tanks have a limited acceptance volume, requiring a larger tank. The diaphragm is not replaceable and the tank has a lower maximum temperature than the plain steel tank because of the material of the diaphragm.

If an expansion tank is required, installation is relatively simple and can be completed in less than 30 minutes. Most "handy" homeowners have all the skills required to get the job done, but a plumber can be called if you run into trouble or feel uncomfortable with the process.