Question: I just saw your answer in the Sun Day to my question. You avoided the question, or possibly you did not understand…The question is: What is the purpose or function of expansion tank? Simple question?
Answer: A standard tank water heater can stress your plumbing pipes by the normal thermal expansion that happens during the heating process. A safety device known as a water heater expansion tank(sometimes called a thermal expansion tank)can help minimize the risk of pressure damage to the plumbing system. (This is normally not a problem with on-demand, tankless water heaters – only tank-style heaters are subject to this problem.)
The water heater expansion tank serves as an overflow receptacle by absorbing excess water volume created by the tank water heater when heating water, as well as absorbing fluctuations in the incoming water supply pressure. Since water expands when it is heated due to thermal expansion, the water heater creates extra water volume every time it heats water. It’s estimated, for example, that the cold water in a standard 50-gallon water heater expands to 52 gallons when heated to 120 F. This extra water volume can create excess pressure in the plumbing system, and if the increased pressure is enough it may, over time, cause damage to the water heater, plumbing fixtures and the water pipes themselves.
Closed Water Supply Systems
In an open system, where expanding water can push back into the city water supply, there is rarely any problem. However, many homes have a closed water supply system, which is a water system equipped with a one-way valve such as a backflow valve, check valve or pressure-reducing valve.In a closed system, this extra water pressure from thermal expansion can cause the most damage because the extra water pressure cannot push back into the city water supply and therefore has nowhere to go.
Most cities, including Huntley, require that residential closed plumbing systems be equipped with expansion tanks. If you have some form of backflow preventer installed (this backflow preventer valve is built into the water meters in Huntley) on the main water line, you may be required by law to also have a water heater expansion tank installed.
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