This question is an exact duplicate of:
The goal is to have a non-invasive flow meter that I can clamp over hydraulic lines.
As a student of hydraulics, I ended up looking and poking around for a good way to make an ultrasonic flow sensor with Arduino and possibly the hc-sr04. Not married to either idea.
So, I admit, I know nothing, but is it possible to do this?
Is there an easier way?