What Are the Different Types of Vessels?

An expansion vessel is a pressurised vessel that incorporates a bladder or diaphragm in its design and is installed in unvented heating, cooling, potable water and solar heating systems. These are also referred to by some manufacturers as Expansion Tanks or Pressure Vessels.

A standard expansion vessel consists of a pressure vessel, water system connection, air valve and a membrane (diaphragm) or bladder. The membrane or bladder separates the pre-charged air or nitrogen from the system water.
However, different expansion vessels are designed for the different types of systems that they are installed into. It is important to know the differences between each type of expansion vessel and how they work on their specific system type.

There are three main types of expansion vessels:

• Heating
• Potable
• Flow Through

Heating

Heating vessels are designed to allow the water to sit within the metallic body and there is then a diaphragm which holds the pre-charge.

Potable

Potable vessels work using the same method however the water sits within a rubber bladder, this is due to the fact that the potable water (wholesome water) cannot sit against the metal due to it being oxygenated water.

Flow Through

Flow through vessels are designed in a similar way to potable vessels however there is a special “mushroom” shaped insert which encourages flow through the vessel and not allowing any stagnation. However, there are also flow through vessels where there is a top and bottom connection and the water flows directly through the vessel.