What is your expansion tank used for?

The “official” start of the heating season is November 1st, but with this post we anticipate that this will be the first series to explain the different equipment and elements that make up heating or domestic hot water (DHW) installation, so when you see them, you can easily find them.

Let’s start with Glass expansion, a type of glass that is usually red.

What is an expansion tank?

AND security element any equipment connected to a closed circuit containing heat transfer fluid.

In our case, we will focus on heating and hot water circuits, so the function of the expansion tank for absorbs increased water pressure which is in those circles When is it water temperature when the boiler is started and vice versa when it is reduced.

A simpler explanation, when water heats up, it expands as its volume increases, which can lead to a dangerous situation for the equipment, therefore to solve this problem the equipment must be placed on one or more expansion vessels that absorb this increase in volume.

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Types of expansion tank

Open expansion vessel

An open expansion vessel is a reservoir that It must be placed in the highest part of the installation. It is important that the water in this tank is in as little contact with air as possible, because if it is supplied with oxygen, it helps oxidize the components of the installation when it enters.

An open expansion tank often needs a device that prevents the water it contains from freezing, which can happen because it must be above, above the heated area.

This type of expansion vessel no longer works in favor of closed tanks for a number of reasons not already mentioned:

Check Difficulty of installation compared to housings, which can be installed in the boiler room itself.

Check Long pipes should be placed between the boiler and the tank, the height of which should be above the highest radiators.


Closed expansion vessel

The closed expansion vessel has metal tank divided into two zones inside thanks to the flexible waterproof membrane.

One zone is in contact with the primary heating circuit, so it is full of water, and the other zone is filled with another liquid: air or inert gas under operating pressure.



There are 2 types in this expansion tank:


Check Fixed membrane

Check Interchangeable membrane

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We will focus on the operation of a closed expansion vessel, which is commonly used in heating and hot water circuits.

As mentioned earlier, when the temperature of the heat transfer fluid increases, the pressure also increases and the fluid expands in the tank, moving the flexible membrane downward, thus reducing the volume occupied by the gas.

If the process that occurs is the opposite, that is, instead of the temperature rising, it decreases, the pressure also drops, moving the membrane upwards increases the volume occupied by the gas.

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We hope this article has helped you learn more about installation.

Is there anything else that piques your curiosity?