What is the expansion tank used for?

The « official » start of the heating season is November 1st, but with this entry we expect it to be the first in a row to explain the various amenities and items that make up a Heating or hot water installation, When you see them, you can find them easily.

Let’s start with Glass expansion, the kind of glass that is usually red.

Source: Ibaiondo

What is an expansion ship?

ON Security element All devices that are connected to a closed circuit and contain a heat transfer fluid.

In our case we concentrate on the heating and hot water circuits, so the function of the expansion tank is closed absorbs the increased water pressure What’s in these circuits when is it the water temperature when the boiler starts and vice versa when it decreases.

A simpler explanation When water is heated, it expands and increases in volumeTo solve this problem, the device must be mounted on one or more expansion vessels that absorb this increase in volume.

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Types of expansion tanks

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 comes into contact with air as little as possible. When oxygenated it helps oxidize the components of the plant when it returns to the system.

An open expansion tank must often have a device that prevents the water from freezing. This can happen because it has to be above the heated area.

This type of expansion vessel is increasingly not working for closed vessels for a number of reasons other than those already mentioned, such as:

Installation difficulties compared to enclosures that can be installed in the boiler room itself.

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


Closed expansion vessel

The closed expansion vessel has Metal tank divided into two zones thanks to a flexible waterproof membrane.

One zone is in contact with the primary heating circuit, i.e. it is full of water, and the second zone is filled with another liquid: air or an inert gas at operating pressure.



There are 2 types in this expansion tank:


The solid membrane

The replaceable membrane

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

As already mentioned, as the temperature of the heat transfer fluid rises, so does its pressure and the fluid expands in the glass, thereby moving the flexible membrane downwards, thereby reducing the volume occupied by the gas.

If the resulting process is reversed, that is, instead of increasing the temperature, it will decrease, the pressure will also decrease and the membrane will move upwards, increasing the volume occupied by the gas.

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

Is there anything else that arouses your curiosity?