Which device activates the fill pump when the water in the tank is low?

The device that activates the fill pump when the water in the tank is low is the float. Floats are designed to rise and fall with the changing water levels; when the water falls below a certain threshold, the float drops to a specific position which triggers a switch or sensor to activate the fill pump. This mechanism is crucial for maintaining the proper water level in the tank and ensuring that the sprinkler system operates efficiently without running dry.

Floats are commonly used in various applications for water level control, making them highly reliable for this purpose. They provide a simple yet effective method of monitoring water levels and ensuring that the fill pump operates only when necessary, thereby conserving energy and resources.