Why do we need expansion tanks?
Expansion Tanks & Pressurisation systems are critical to the successful operation of heating and cooling circuits and must essentially fulfil three fundamental tasks:
- Maintaining the pressure within permissible limits at every point of the system, that is, the permissible working pressure must not be exceeded as well as maintaining a minimum pressure to prevent vacuum, cavitation and evaporation of the system liquid, e.g. in circuits with superheated water, solar systems.
- To prevent a negative pressure at the highest points of the installation in order to avoid the intrusion of air into the piping network.
- Compensation of volume fluctuations of the heating or cooling water due to temperature fluctuations.
- Providing a water seal to prevent system-related water losses.
With any heating or chilled water system there is expansion and contraction as the system water is heated or cooled. Because water is incompressible, the pressure in the system will increase or decrease accordingly. To prevent damage to the system components, expansion tanks are installed which contains the excess volume as the water heats and expands and allow that water to fill the vacuum created when the system water cools and contracts.
Careful calculation, commissioning and maintenance are the prerequisite for the correct functioning of the overall system.

Duraflex Forte diaphragm type expansion vessels were installed to service the HHW Central Plant expansion system for the upgrade of Melbourne’s iconic Chadstone Shopping Centre