Hydraulic Line Fluid Velocity and Minimum ID
The hose-sizing check the hydraulics bench never had: V = 0.3208 Q / A, with the constant derived from 231 in^3 per gallon rather than tabulated. 20 gpm through a 5/8-in ID runs 20.9 ft/s - over the pressure ceiling, needing 0.674 in. Suction is the band that punishes you: too fast and the pump cavitates. Published bands DISAGREE (return 4-13 vs 10-15, pressure 7-18 vs 15-20), so the ceiling is editable and both sets are named. Also gives the minimum ID and the max flow for the line you have.
Formula and source
V (ft/s) = [231 / (60 x 12)] x Q (gpm) / A (in^2) = 0.3208333 Q / A, A = pi/4 ID^2; minimum ID at a ceiling = sqrt(4 (K Q / Vmax) / pi); maximum flow = Vmax A / K.
Continuity with derived unit conversion (231 cubic inches per gallon, 60 s/min, 12 in/ft) plus industry recommended-velocity bands, named as conventions rather than a standard.
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