These bell or barrel type flowmeters have a BIG pressure drop across them; definitely for testing out different block designs at 0.5-1.5GPM and not for plumbing into a regular cooling loop. I just looked at the sheet that came with my King Instruments flowmeter and it was absolutely no help as far as pressure drop goes. Just has a lot of info on how to properly plumb and place them.
The one I have is from mcmaster-carr. I used it probably 10 times and then it went on a shelf as I got a nicer paddlewheel type that is digital and with much better accuracy. It has 1/2" NPT fittings on both ends and has 0.4-5GPM markings in 0.2GPM increments. Not great, but worked ok for being able to test different blocks at close to the same flow rates.
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