What is the function of an expansion tank in a water system?

The function of an expansion tank in a water system is primarily to absorb changes in water volume. This tank is designed to accommodate fluctuations in water pressure and volume that occur, particularly as water heats up and expands. When water is heated, it expands, and without a designated space to accommodate this change, pressure can build up within the plumbing system. The expansion tank provides a safe space for this excess volume, protecting the pipes and other components of the water system from damage due to excess pressure.

In systems where heating occurs, such as in boilers or water heaters, the expansion tank acts as a cushion, allowing the system to maintain a stable pressure. This not only preserves the integrity of the system but also ensures efficient operation. Therefore, option B accurately describes the primary role of an expansion tank. Other options do not align with the specific mechanical responsibilities of an expansion tank within a water system.