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Thermal Expansion Within the Plumbing System

Davidson Water, Inc. requires the installation of a backflow prevention device within your water meter box in order to protect the distribution system from potential cross connections or backflow from a customer. Such cross connections or backflow could result in pollution and/or contamination of the water system.

When a backflow preventer device is installed in your meter box, water from the building/house will be unable to flow back into the water system. The backflow preventer creates an isolated or closed plumbing system. For some homeowners, thermal expansion could produce leaky faucets or set off the relief valve on hot water heaters, or in some cases, other damage may occur. Thermal expansion occurs when your hot water heater heats the water, causing it to expand.

In order to control thermal expansion, simply lowering the temperature setting of the hot water tank to 115-125 degrees (which is sufficient for most purposes) might reduce the possibility of thermal expansion.

A plumber may recommend the installation of one of the following two types of products to control thermal expansion:

Thermal expansion tank on your hot water heater. Layout shown below is for demonstration purposes only.

A toilet tank ball cock fill valve,anti-siphon backflow preventer and thermal expansion relief valve, all in a single assembly.

A pressure-reducing valve may also be required if your water pressure exceeds 70 psi (pounds per square inch).

Davidson Water, Inc. is dedicated to providing you with superior quality drinking water that exceeds federal standards. With the installation of a backflow preventer after your water meter, you can feel confident that we are protecting you and your family as well as your neighbors and community.

For more information regarding thermal expansion and thermal expansion products you can view this pamphlet from a manufacturer of thermal expansion products.

Why would anyone need an expansion tank?
Water is incompressible. Unlike air, it's impossible to squeeze any quantity of water into a smaller volume. Where that matters is in "closed" water systems such as a water heater with a check valve (pressure regulator and the like) ahead of the heater. When the water gets heated it expands and that extra volume has to go someplace. Without an expansion tank the pressure could rise to a dangerous level in a closed system. A diaphragm type of expansion tank (such as what we sell) is a pressure vessel that contains a flexible membrane totally separating the water from a captive volume of air. Air compresses and as the water temperature rises, creating extra pressure/space, the air in the vessel accommodates that increase. Thereby preventing a potentially dangerous pressure rise.

Why is there a hole near the top of some diptubes?
The reason for the hole is to break siphonage effect when the water is shut off and there is a drain down situation (caused by such things as a valve or a leak that is below the water heater). A common example would be in a mobile home water heater, where the water supply is nearly almost always under the floor. If the water gets shutoff (for whatever reason), without that hole, the diptube could possibly backsiphon (empty most of the water and drain it to the level of the inlet on the coldwater diptube), burning up the elements or possibly allowing the gas burners to damage the near empty water heater. Bottom line, it's for safety.

I have a rattling sound coming from my water heater when the hot water is running?
Check to see if you have check valve type nipples installed on the top of your water heater. They generally look like ordinary galvanized nipples and so sometimes it is hard to tell if they are installed. Some water heaters come with them. They are a great idea because they can save some energy, but they also can be very annoying.

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