Construction of the expansion tank

Closed expansion tank

The device of the expansion tank is a sealed steel vessel divided by an elastic waterproof membrane into two parts. One part has a fitting for connection to the heating system, and the other part is filled with gas (usually nitrogen). The gas part has a nipple necessary for creating initial pressure.

In membrane expansion tanks, water does not come into contact with air, which significantly reduces its corrosion activity, and the pressure in the tank and heating system can vary in a wide range. Closed tanks are not demanding in terms of installation, they can be installed horizontally or vertically, have a flat or cylindrical body, stand on legs or be attached to a wall.

The membrane can be replaceable or non-replaceable. The price of expansion tanks with a replaceable membrane is higher than the price of a tank of the same volume but with a non-replaceable membrane, but in case of membrane rupture, there is no need to replace the entire tank. In addition, in expansion tanks with a replaceable membrane, water does not come into contact with the inner surface of the tank, which is an additional protection against corrosion.

Butyl membrane is used in expansion tanks for water with a temperature from -10°C to +100°C and is less elastic than rubber but more durable.

EPDM membrane is a membrane made of ethylene propylene and is installed at a water temperature from -10°C to +100°C, and like a rubber membrane, does not exclude water diffusion.

Rubber membrane is usually used in hydroaccumulators for water with a temperature from -10°C to +50°C. It is elastic and not durable, and over time water diffusion is possible. Expansion tanks with a rubber membrane are usually not included.

Advantages of membrane expansion tanks

Avoids the absorption of air by water
Can be installed in any part of the heating system
Not demanding in installation and has various designs
Wide range of permissible pressures in the heating system

Disadvantages of membrane expansion tanks

Membrane rupture is possible
A safety valve is required
Pressure in the heating system varies depending on the water temperature
The price of membrane expansion tanks is higher than that of open vessels

Membrane expansion tanks are widely used in modern heating systems and have practically replaced open-type tanks.

Open expansion tank

Construction of an open expansion tank - a steel tank with a hatch at the top, two pipes at the bottom, and one in the middle of the tank. Two pipes at the bottom are necessary for creating water circulation through the tank, and the middle pipe is used to control the water level and is discharged through a drain valve. Non-pressurized expansion tanks have been used in water heating systems since their inception and were installed in attics or stairwells of buildings.

Advantages of non-pressurized expansion tanks