Expansionstank

Expansionstank is a term used to describe a pressure vessel designed to absorb the volume change of a liquid in a closed system due to temperature variation. In hydronic heating and cooling networks, liquids expand as they heat, and without an expansionstank the resulting pressure rise can stress pipes, valves, and safety devices. The expansionstank provides a compressible cushion to maintain safe, stable system pressure.

Construction and operation: Most expansionstanks consist of a steel shell divided by a bladder or diaphragm. One side holds air or an inert gas under a pre-set pressure; the other side contains the system fluid. As the fluid expands, the gas is compressed, which keeps pressure within design limits and allows the system to regain its original volume when cooling occurs.

Variants and sizing: Bladder-type and diaphragm-type tanks are the most common forms. Some systems use a simple air chamber, though this is less common in modern installations. Sizing depends on the system fluid volume, the maximum allowable pressure rise, and the expected temperature range.

Installation and maintenance: Expansionstanks are typically located on the supply or return line of the system. The tank is pre-charged to a specified pressure during cold installation; this charge should be checked after initial filling and periodically thereafter. Over time the bladder can degrade and the tank may become waterlogged, reducing effectiveness and requiring replacement.

See also: expansion vessel, pressure vessel. Expansionstanks are widely used in building services and industrial processes to protect components and improve efficiency.