Expansion Vessel (MEV)

Membrane Expansion Vessels (MEV) are designed to compensate volume and pressure changes caused by temperature changes in closed water circuits. An elastic membrane inside the MEV divides a gas pressurized compartment from a water filled compartment, which is directly coupled to the water current. If the system is heating, the expanding water enters the last mentioned compartment. When cooling down, the water is flowing out.

MEVs are used in central heating systems, but also in solar thermal systems, where a fluid transports the heat from the Collector to the Solar Storage Tank. They are an important engineered safeguard, e.g. if after some hot and sunny days the storage capacity of the solar tank is exhausted and the system shuts down. The MEV of a solar system should be able to contain the whole fluid content of the collectors.

In so-called Drainback Systems (DBS) the MEV is replaced by a drainback vessel.

Page: 8 of 8