What is one function of a plumbing expansion tank?

An expansion tank serves a critical role in a plumbing system by absorbing excess pressure created from thermal expansion of water. When water is heated, it expands, and this increase in volume can cause a rise in pressure within the plumbing system if there is no open space for the expanded water to go. The expansion tank provides a cushion for this extra volume. It typically contains a flexible diaphragm or bladder that separates the air and water. As water expands, it enters the tank and compresses the air, which helps to maintain a manageable pressure level within the system, preventing potential damage or leaks from over-pressurization. This function is essential for maintaining the integrity and safety of both the plumbing infrastructure and the appliances connected to it.