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Originally Posted by bigben2k
It's really not hard to see (even without an implant!) that loosing 10" of pressure would be a real waste of pumping power, when 1/2" tubing would only drop 2.5 inches. Given that our pumps are relatively weak, especially on the pressure side, IMO, every bit counts. As a bonus, if one ever upgrades the pump, 1/2" tubing can easily handle up to 3 gpm, dropping about 9" H2O of pressure, resulting in a flow speed of 4.9 feet per second.
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I did the calculation too, tho i used Haaland's correlation to calculate the friction factor (which change with Re and hence velocity) and used a e=0.0015mm (drawn plastic tubing) and got results similar to yours. But that was not my point. My question is rather why the 1.5gpm mark? Why not 1.3? 1.4? 1.6?... and so on. I mean, for pretty much any flow rate, the loss in a 3/8 tubing will be around 4 times what you will have with 1/2 tubing. The 1.5gpm mark you choose seems a little arbitrary. The best that can be done with results like these, imo, is to show the curves you calculate and let others choose for themselves.