I'm setting up a control system for a small scale biofuel processing rig. Part of the task is to monitor the flow rate of feedstock. Due to budget constraints, I could not simply buy and industrial grade sensor. So, I'm evaluating this low cost sensor for low flow rate and more viscous fluid [than water].
This type of low-cost paddle wheel flow meter is sold by Adafruit among other places.
The static o-ring, which seals the paddle wheel cavity, is visible on the lid. The latter also serves as the bottom of the PCB compartment.
At the end of the paddle wheel sits the magnet. The outside diameter of the magnet is 9.7mm .
The o-ring in this photo prevents liquid ingress into PCB compartment. This is the 2nd o-ring in this device, and not the main one that seals the paddle cavity.
ReassemblyAfter this teardown, the reassembled sensor continued to work like new.
RelatedSensors Magazine article on paddlewheel flow sensors
Higher precision paddle wheel flow sensors made by Omega Engineering