How Does an Expansion Tank Work - What is an expansion and how does it work? I get that question all the time even though I have written an extensive article on expansion tanks. ┬áThe two most common expansion tanks you will see in HVAC applications include the bladder type expansion tank and the steel type expansion tank. ┬áThe steel type expansion tank needs some basic maintenance from time to time to ensure it doesn’t become waterlogged or overfilled which would defeat the purpose of having an expansion tank. For more on the basic maintenance of a steel expansion tank and how to properly fill it check out this article.

How Does an Expansion Tank Work

How Does an Expansion Tank Work

The difference between a steel expansion tank and a bladder type expansion tank.

How does an expansion tank work and why do you need one in your boiler or chilled water system? If you have a hot water boiler system (not a low-pressure steam boiler - there is a huge difference between the two) or a chilled water system (not many chilled water systems in residential but I have seen them) then you have a closed loop piping system that runs to either convectors, radiators, or a coil or two somewhere in the system where the main heat exchange process takes place. Inside this piping is water (sometimes a water/glycol mix but that is mainly in commercial applications) and when water heats and cools down it expands and contracts. The piping system along with the parts of the boiler or chiller that have water cannot handle this expansion and contraction with breaking or busting open. Therefore in every hydronic system, there is an expansion tank to handle this expansion and contraction. An expansion tank is basically a shock absorber that absorbs this expansion and contraction of the volume of the water.

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How Does an Expansion Tank Work

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