What is a valve or faucet that closes automatically when released manually known as?

A valve or faucet that closes automatically when released manually is known as a quick closing valve. This type of valve is designed to enhance safety and conserve water by ensuring that the flow is cut off immediately once the user is no longer holding it open. Quick closing valves are often used in applications where immediate shut-off is critical, such as in emergency situations or in facilities that require strict control over water usage.

The other types of valves listed have different functions. A pressure relief valve is specifically designed to release pressure from a system to prevent damage, typically used in systems where pressure can build up. A regulating valve is used to control the pressure and flow rate within a plumbing system, maintaining a desired set pressure. A flow control valve helps to manage the flow of fluid in a system, but it does not automatically shut off the flow when released. Thus, the characteristics of a quick closing valve are distinct, making it the correct answer.