I have found the Technical Specifications for my flow sensor, which can be found at http://www.nymet.com.au/valves/1flowsensor.html
Flow Range: 2 – 100 LPM
Repeatability <= 1%
Accuracy <=2.5% of FULL SCALE
Max. fluid temperature: 60 DEG C
Max. Ambient Temp. Range: 0 DEG C – +60 DEG C
Max. Fluid Pressure: 1.5 Mpa
Operating Voltage: +5V – + 24V
Output Frequency: Square Wave
Would this be compatible with OpenSprinkler?