Closed Expansion Vessels (tanks)

When heating water warms up, its volume increases. A closed expansion vessel absorbs this extra volume with a membrane and pressurised air, so that circuit pressure stays within safe limits and the safety valve does not keep opening.

Capacity is chosen according to the system’s water volume (boiler, pipes, radiators) and operating temperature, and the pre-charge pressure is set according to the height of the building. You will find Zilmet vessels in various sizes, and the Mastersol vessel for the closed circuit of a solar water heater.