Why are expansion tanks used in plumbing systems?

Expansion tanks play a crucial role in plumbing systems, especially in closed water heating systems. The primary function of an expansion tank is to absorb excess pressure generated by the thermal expansion of water when it is heated. As water heats up, it expands, leading to increased pressure within the plumbing system. If this pressure is not managed, it can strain pipes, fittings, and other components, potentially causing leaks or failures.

The expansion tank provides a space for this expanded water to go, thus mitigating the pressure buildup. It contains a diaphragm or bladder that separates the air and water in the tank, allowing for the absorption of excess pressure while maintaining normal system operation. This design helps protect the plumbing system from damage and ensures a reliable water supply without risk of ruptures or unwanted leaks.

The other options do not accurately reflect the function of expansion tanks; they do not increase water pressure, supply emergency water, or filter water. By focusing on the need to manage pressure resulting from thermal expansion, the use of an expansion tank becomes essential in maintaining a safe and efficient plumbing system.