An expansion tank or expansion vessel is a small tank used to protect closed water heating systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibility cushions shock caused by water hammer and absorbs excess water pressure caused by thermal expansion.
Expansion tank in a central heating system
Expansion tank in a 1987 Saab 90 (brown plastic tank with white lid at top of picture)
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
A small tank water heater
Electric-tank–type storage water heater (US)
Gas furnace (top) and storage water heater (bottom) (Germany)
The inside of a hydraulically operated two-stage tankless heater, heated by single phase electric power. The copper tank contains heating elements with 7.2 kW maximum power.