Pressure vessels, also called expansion tanks, are used in all forms of pumped systems. The pressure in the vessel increases after the pump switches on. The pump switches off when the vessel is filled to capacity and has reached its highest pressure setting. As water is drawn from the vessel, the pressure inside decreases until it reaches a minimum setting. At this point the pump switches on again.
The Grundfos GT-H and GT-D type tanks have a sealed in, heavy duty diaphragm that separates air and water in the tank. Grundfos GT-U type tanks have a replaceable bladder that separates nitrogen and water. Both the bladder and the membrane allow the tank to be pre-pressurised before it leaves the factory. They also prevent water contamination, erosion of the tank or loss of pressure in the tank system.
When water flows into the tank, the diaphragm or bladder flexes and compresses the cushion of air or nitrogen behind it. The pressure inside the tank increases and equals the pressure provided by the pump. The water pressure in the tank and the air or nitrogen pressure behind the diaphragm or bladder is always the same. This dividing membrane is never under strain. It always allows a precise amount of water to flow into the tank as determined by the setting on the pressure switch.
Grundfos pressure vessels are long life and maintenance free. They can be integrated easily in systems with a variety of pump types, although Grundfos pressure vessel pumps would be the best option.