This is a YF-S402B Water Flow Sensor that works on 5-24V with a Flowmeter 0.3-6L/Min. This 1/4 inch water flow sensor is basically a small turbine whose output signal is a series of digital pulses. The frequency of the pulses is proportional to the flow rate of the liquid passing through the sensor. That digital signal, whose frequency is in the range between 0Hz and 100Hz, can be read directly through one of the digital input/output pins of a microcontroller.
1 x Water Flow Sensor YF-S402B ( 5-24V, 0.3-6L/Min)