Design of the expansion vessel

An expansion vessel is a sealed tank whose volume is divided by an elastic membrane. On one side of the membrane is a closed volume of air, and on the other side is water from the water supply system.

Expansion vessels are similar to expansion tanks for heating systems, but they can only be used with cold drinking water, while expansion tanks can be used with cold and hot technical water.

The body of the expansion vessel is made of stainless or carbon steel. The inner and outer surfaces of the tanks are covered with an anti-corrosion paint that is permissible for use with drinking water.

Membrane material:

• Rubber membranes are used in expansion vessels for water with a temperature from -10°C to +50°C. They are elastic but not very durable, so water diffusion can occur over time.
• Butyl membranes are used in expansion vessels for water with a temperature from -10°C to +100°C. They have less elasticity than rubber membranes but greater durability.
• EPDM membrane made of ethylene propylene is installed in expansion vessels for water with a temperature from -10°C to +100°C and, like rubber, does not exclude water diffusion.

The membrane can be replaceable or non-replaceable. The price of an expansion vessel with a replaceable membrane is higher than the price of a tank with the same volume but with a stationary membrane, but in case of membrane rupture, it will not be necessary to replace the entire tank. In addition, in expansion vessels with a replaceable membrane, water does not come into contact with the inner surface of the tank, which is an additional protection against corrosion.

Some expansion vessels can be equipped with a pressure gauge, a membrane rupture sensor, and devices that provide circulation in the tank, preventing water stagnation.

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