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Originally Posted by prandtl
what exactly made you choose 1.5gpm as the "limit"? Do you have a link to the thread where you stated it first, wich, i suppose, also show the reasons behind the 1.5gpm...
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Reticular implant aside...
You want to keep the flow speed under 5 feet per second, otherwise the pressure drop becomes significant.
Using Hazen-Williams and a friction factor of 140 (smooth copper), here are the pressure drops at various flow rates, for a 3 foot long section of tubing:
1.0 gpm (60 gph)
1/4": 34" H2O pressure drop, 6.5 fps (feet per second) flow speed
3/8": 4.7" H2O, 2.9 fps
1/2": 1.2" H2O, 1.6 fps
1.5 gpm (90 gph)
1/4": 72" H2O, 9.8 fps (!)
3/8": 10" H2O, 4.4 fps
1/2": 2.5" H2O, 2.5 fps
2.0 gpm (120 gph)
1/4": 122" H2O , 13.1 fps (!)
3/8": 17" H2O, 5.8 fps (!)
1/2": 4.2" H2O, 3.3 fps
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.
Note: Hazen-Williams may not be the best formulae to calculate this, but should be pretty close to real figures.
PS: I believe I've posted the Excel sheet with this formulae. If interested, I'll post it again.