What is the purpose of a hammer arrestor in plumbing systems and how does it prevent water hammer?

A hammer arrestor in Plumbing systems is used to prevent water hammer, which is the loud banging noise that occurs when water flow is suddenly stopped. The purpose of a hammer arrestor is to absorb the shock caused by the sudden stoppage of water flow, preventing damage to pipes and fixtures. It does this by providing a cushion of air or gas that absorbs the pressure surge, reducing the impact and noise of water hammer.