• Model : SEN-HZ21WI (YF-B3)
  
• Water quality requirement : Drinking water health standards, 0～80℃
  
• Flow range : 1～ 25 Liter/min
  
• Withstand hydraulic pressure : ≤1.75 MPa
  
• Voltage/electric current : DC4.5～18V, ≤15mA
  
• Insulation resistance : >100MΩ
  
• Electrical strength : AC500V, 50HZ
  
• Output level : Rated voltage DC 5 Volt, high level ≥4.5 Volt, low level ≤ 0.5 Volt
  
• Pulse duty cycle : 50%
  
• Flow characteristic : F=10 Q-4, F:HZ, Q:L/min，±10%
  
• Cumulative flow conversion : 1 Liter water = 553 pulses , accuracy: 10%

This water flow sensor is connected in line with the liquid whose flow rate has to be measured. There is a simple rotating wheel with a magnet and when the liquid flows the wheel is rotated and a hall effect sensor measures how many times he wheel is rotated and accordingly gives pulses. By counting the number of pulses you can easily calculate the flow rate as well as the amount of liquid dispensed