At present, liquid level control type is one of the most popular control methods in the application of elevated tank water-supply and sewage and rain drainage system. It measures liquid level by floating ball switch (or other liquid level meter), and then feedbacks the signal to control panel in order to control the start-stop of the pump. It has protection functions such as short circuit, stop-phase and overload. For submersible motor it can also add protection functions such as electric leakage, pump casing water leakage and motor stator winding overheat. It is an automatic control device which is economical, reliable and easy to maintain.