The positive or negative signals from the sensor control the solenoid valve. The polarity of the signal determines if the solenoid will either engage a pull or push actions. The valves control the water flow by using a rubber-like disc. When there is no signal, the valve is closed, meaning no water flow through the valve. The presence of a hand will send a positive signal to the solenoid causing it to pull the valve open for water to flow. The solenoid will close up the valve by a push action when the hand is no more.