We just bought a house and there is a well on the property. Of course, there is a pump to get the water out of the well and into the house but there is also this red thing in the “well house.” Reverse image search tells me it’s an expansion tank (the brand is Elbi) but I don’t understand exactly what purpose it serves. Can you explain it?
In: Physics
The tank has a bunch of air in it (probably inside a flexible bladder), as well as water. When the pump forces water into the expansion tank, the air compresses until it reaches a predetermined cut-out setting of a certain psi and toggles a switch to stop the pump. This creates pressure in the water lines. When you open a faucet, water flows and reduces the pressure until a cut-in pressure point is reached, and the pumps starts up again. This makes it easier on the pump by ensuring it doesn’t have to run every time a tap is turned on for a few seconds because starting a pump when the system is under pressure is not an easy job. If there was no expansion tank, even a dripping faucet could make life very hard on the pump. The larger the expansion tank, the better, in most cases.
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