Is this sensor able to measure flow in any direction or only on the arrow's one ?

Hello, please how do i code two flowsensors so that i can initialize a condition that if the flow rate is different i can know for leakage detection
http://bigbelectronics.in/product.php?product=water-flow-sensor

What is the pulse signal NPN or PNP?

Yes, the ±5% accuracy is fit for 0.3-3L/min flow speed, and the water pressure is less than 0.8 MPa.