What does an expansion tank do in a plumbing system?

An expansion tank plays a critical role in managing excess pressure within a closed plumbing system. When water is heated—such as in a water heater—it expands. In a closed system, this expansion can lead to an increase in pressure, which may exceed the safe operating limits of the pipes and fixtures.

The expansion tank is designed specifically to absorb this excess pressure, providing a cushion that allows the expanded water to flow into the tank rather than causing potentially damaging pressure surges throughout the plumbing system. This helps to maintain safe and stable pressure levels, ultimately protecting pipes, fittings, and appliances from stress and potential failure.

Other options do not accurately describe the function of an expansion tank. For instance, while water filtration is an important aspect of some plumbing systems, it is not the function of an expansion tank. Additionally, increasing water temperature is unrelated to the purpose of an expansion tank, which does not heat water but addresses pressure changes. Similarly, while having additional water supply in a system is beneficial, this is not the role of an expansion tank; other components like tanks or reservoirs fulfill that function. Thus, the choice regarding the absorption of excess pressure is fundamentally correct as it highlights the primary purpose of the expansion tank in plumbing systems.