The YF-S201 water flow sensor consists of a plastic valve body, flow rotor and hall effect sensor. It is usually used at the inlet end to detect the amount of flow.

When liquid flows through the sensor, a magnetic rotor will rotate and the rate of rotation will vary with the rate of flow. The hall effect sensor will then output a pulse width signal. Connect it to a microcontroller and you can monitor multiple devices such as your coffee maker, sprinkler or anything else, and control the water flow rate to suit your needs!

The Gravity interface make it be compatible with Arduino IO Expansion Shield.

Note:
*A 20 mm rifled pipe is recommended
*Avoid unit contact with corrosive chemicals
*The unit must be installed vertically, tilted no more than 5 degrees
*Liquid temperature should be less than 120 C to avoid damage to unit

• Inner Diameter: 11 mm
• Outside diameter: 20 mm
• Proof Water Pressure: <1.75 MPa
• Water Flow Range: 1-30 L/min
• Voltage Range: 3.5~12 V
• Operating Current: 15 mA (DC 5V)
• Insulation Resistance: >100 MΩ
• Accuracy: ±5% (2~30L/min)
• The Output Pulse High Level: >4.7 VDC (DC input voltage 5 V)
• The Output Pulse Low Level: <0.5 VDC (DC input voltage 5 V)
• Output Pulse Duty Ratio: 50% ± 10%
• Water-flow Formula: 1L = 450 square waves
• Working Humidity Range: 25% ~ 95% RH (no frost)
• Dimension: 62*36*35 mm/2.44*1.37*1.37 inches
• Weight: 52g

• Product WIKI 

• Gravity - Water Flow Sensor - 1/2" x1