One nice thing about paddle wheel flowmeters is that they're like a good old fashioned 'visual flow indicator' : walk into a room, take a quick or lazy glance that a-way, and feel reassured. Ones with clear plasic or glass on both sides of the rotor let you mount an LED behind them so you can do this in the dark.
If you can take the face off to remove a stray string of teflon tape or whatnot without having to pull it from the loop, that can be convenient too.
Plastics like nylon that can soak up surficants, antioxidants, anticorrosives, whatnot beyond my chemistry / materials testing are a bummer.
Is there a reliable spec. for the bottom end of pulses / sec. that an hypothetical generic fan header should be expected to sense? ( I have a gems rota-flow installed on one old MB that can't sense as slow as the flowmeter signals; it's a fanles / silent rig that could get by on 0.5 lpm. )
Tangent: I'd write off designing a flowmeter around producing an off the shelf correlation between 4-20 mA pulses / sec and lpm or ml/s or gpm of a particular coolant mix of a particular viscosity with a particular thermal conductivity at a particular temperature and pressure. Like 'low cost flowmeter' on the one hand and the lab kit and skills to establish all that on the other...
I suppose it would be possible to design one that worked in only one flow direction, or was good at trapping bubbles in any but one precise vertical alignment -- that would be sad.
That's what comes to mind this afternoon for someone trying to design / build / sell a low-cost paddle wheel meter for this niche.
Price / performance wise the Swissflow does look interesting, and if it puts out a ball park accurate flow based on a common fan divider, well that is nice indeed.
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