What is the purpose of an expansion tank in a steam system?

The purpose of an expansion tank in a steam system is to accommodate the expansion of water as it heats, preventing pressure build-up. As water is heated and converted into steam, it expands significantly. If there were no expansion tank to absorb this expansion, the increasing pressure within the system could lead to equipment damage or failure due to excessive pressure levels.

The expansion tank provides a space that allows for the increased volume of water and steam, which helps maintain a constant pressure throughout the system. Additionally, it allows for compensating for changes in volume as steam condenses back into water. This is essential for the safe and efficient operation of steam systems, as it helps to regulate pressure fluctuations that may occur during operation.

In contrast, the other options do not accurately describe the function of an expansion tank in a steam system. Storing excess steam or filtering impurities are roles associated with different components in a steam system, and monitoring water quality is crucial but managed through specific water treatment systems rather than an expansion tank.