Expansion vessel

Expansion vessel - designed for accumulating hydraulic energy of water and its subsequent use. The hydroaccumulator in the water supply system serves as a damper that can absorb both a volume increase or a sudden pressure surge, as well as compensate for minor water consumption to reduce the frequency of pump operation.

Water is practically incompressible, so even the slightest leakage in the water supply system or the instant opening of a tap will cause a sharp decrease in pressure and subsequent pump activation. The smallest volume increase, even resulting from the expansion of heated water, can lead to a sharp increase in pressure and the destruction of water supply system elements.

The principle of operation of the hydroaccumulator is based on the accumulation of hydraulic energy of water with its subsequent use. During pump operation, part of the energy is spent on compressing the air that fills the internal volume of the tank and filling it with water. After the pump is turned off, the compressed air maintains pressure in the water supply system, and minor water consumption is compensated by water displaced from the tank.

Application area

Hydroaccumulators are used in cold and hot water supply systems for:

• Maintaining pressure in the water supply system.
• Creating a water reserve in systems with water supply interruptions.
• Compensating for temperature expansions that occur during water heating.
• Compensating for hydraulic shocks that occur when the pump is turned on.
• Compensating for minor water consumption or leaks that cause excessive pump activation.
• Smoothing peaks in water consumption in systems with limited instant water flow.

Equivalent names

• Hydroaccumulator
• Hydropneumatic accumulator
• Buffer capacity
• Shock absorber tank
• Expansion tank for water supply

What can be used instead

• The hydroaccumulator can be replaced with an expansion tank, but it should be noted that expansion tanks are designed for hot technical water and are equipped with a less elastic membrane.


• An open reservoir installed at the highest point of the water supply system, where the pump on and off signal should come from level sensors installed in this reservoir. This scheme is quite complex to implement and is usually only used to create a reserve of a large volume of water. An example of an open reservoir is a water tower.