Final answer:
Water hammer is a defect that causes a loud noise when a quick-closing valve is suddenly closed. It is caused by pressure surges and vibrations in the water system. Water hammer arrestors can help reduce or eliminate this issue.
Step-by-step explanation:
The defect that causes a loud noise when a quick-closing valve, such as a clothes washer valve or ball valve, is suddenly closed is called water hammer.
Water hammer is caused by the sudden change in momentum of the water when the valve closes, resulting in pressure surges and vibrations. These pressure surges can create a loud banging or hammering noise, hence the name water hammer.
One way to reduce or eliminate water hammer is by installing devices called water hammer arrestors or shock absorbers, which absorb the pressure surges and prevent the noise.