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Expansion Vessels for Pumps

Expansion Vessels for Pumps

Expansion vessels or pressure vessels as they are sometimes called are used to store water under pressure to reduce the on/off cycling of electric powered pumps.

How it works
Inside the tank is a rubber membrane. On one side of the membrane is compressed gas (air or nitrogen) and on the other side is water. When the pump is started, water is forced into the pressure vessel which causes the membrane to expand, compressing the air on the other side of the membrane. When the set pressure is reached, the pressure switch stops the pump and a non-return valve closes, holding the pressure in the system. When water is drawn from the system, the gas pressure forces water out until the pressure falls to the lower set level of the pressure switch. At which point, the pump re-starts and the cycle is repeated.