What fitting operates automatically to refill the water tank after discharge and shuts off when full?

The fitting that operates automatically to refill the water tank after discharge and shuts off when the tank is full is the float valve. This mechanism uses a buoyant float attached to a valve; as the water level in the tank decreases due to discharge, the float drops, opening the valve to allow water to enter the tank. Once the water level reaches a predetermined level, the float rises, causing the valve to close and stop the flow of water. This automatic functioning makes float valves essential for maintaining consistent water levels in various applications, such as toilets and water tanks, without the need for manual intervention.

The other options serve different functions: the foot valve typically prevents backflow and maintains prime in pumps, the pressure regulating valve is used to control and reduce water pressure, and the check valve permits flow in one direction only, preventing backflow.