What is an expansion vessel

In the next of our series of plumbing articles we’ll have a look at expansion vessels and what is an expansion vessel. Even if you don’t know it’s quite probable that you own one. You will find them on domestic and closed water heating systems. They are actually minnion like shaped tanks.

So what is an expansion vessel and what does it do?

An expansion vessel is fitted to your water heating system to protect it from increases in pressure.  The vessel itself has two sides inside that are separated by a diaphragm made of rubber. One side is connected to the pipework, this side contains water. The other side has air. The vessel being filled with air means that with sudden changes of pressure within the heating system the effect can be cushioned and absorbed. Pressure changes can be caused by the likes of thermal expansion or a sudden pressure change when a valve is closed.

The dry side (or side with air) usually has a valve similar to the likes on a car. This means the pressure can be checked and air added when necessary. You may have heard the term re-pressurizing the system. If you central heating system has a leak or is losing pressure (normally below .5 bar) the rubber diaphragm is pushed towards the water inlet on the wet side of the vessel. Once  the water pressure starts to increase this forces the diaphragm to move and results in it compressing the air on the dry side.

Expansion vessel don’t last for ever. Over a period of time rubber diaphragm may split or tear through years of expansion and contraction. You will then notice a leak. Now we’ve answered the question what is an expansion vessel, is yours in good working order?

If you have any questions or queries about expansion vessels or you need a new one installed just call the experts at plumbers Dublin on 01-6874853.