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 expansion tank acts as a pressure leveler and pressure sustainer.
When the well pump is pumping, it is pumping water up into the piping system. If there are no faucets open, the pressure rises quickly in the pipes and the pump shuts off. If someone now opens a faucet, the pressure drops quickly (because the pipes don’t have much water) and the well pump restarts to build pressure again. In some situations that causes the well pump to cycle on and off repeatedly and this reduces the life of the water pump. The expansion tank holds some water (like a buffer) in a container that gradually pressurizes so this can help reduce the rapid pump cycling.
In reverse there is also an issue if some faucets are turned off quickly while the water pump is running. This causes a pressure spike from the faucet end to travel back towards the pump. This is known as a water hammer – the pump suddenly sees a high pressure feedback from the pipe system potentially damaging it in the long term. The expansion tank can absorb this pressure spike and not allow most of it to hit the pump.
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