Liquid level control. Water level sensor or liquid level switch is installed in the system to monitor the change of liquid level. When the liquid level reaches the preset upper limit or lower limit, the sensor will send a signal to control the start and stop of the sewage pump through the controller. Sewage pump, also known as sewage pump, is a kind of pump product which is connected with motor and works under liquid at the same time. Compared with ordinary horizontal or vertical sewage pumps, sewage pumps are compact in structure and occupy a small area, and are located in the basement of buildings.