Why is an expansion tank used in a well system?

• A. To increase water pressure in the system
• B. To filter and purify water
• C. To absorb thermal expansion of water and prevent pressure spikes that could damage the system
• D. To monitor flow rate

Answer: (C)

In a well system, water expands when it’s heated. If the system is closed and has a pressure tank, that extra volume has nowhere to go, so pressure would rise and stress components like the pump, fittings, and piping. An expansion tank provides a dedicated space where the expanding water can push against an air cushion or a bladder. As water expands, the air compresses, absorbing the surge and smoothing out pressure changes. This prevents damaging pressure spikes, reduces water hammer, and helps the system run more reliably.

This isn’t about increasing pressure, filtering water, or monitoring flow rate, so those other functions don’t fit the situation.