Flow Switch utilizes the force of liquid flow to propel its paddle in order to detect the incoming flow or moving of the existing liquid in pipe. In condition of static liquid or no liquid, the spring is in expanding and press the magnet downward vertically. Reed switch contact is N.O. As flow occurs and the paddle is thrusted and raised at an upward angle of 20~30 deg. (or more), the eccentric of paddle will push the magnet upward to actuate the reed switch which is thus in a close circuit. The length of paddle can be adjusted with the diameter of a pipe.