Velocity Head and Dynamic Pressure
Velocity head h_v = V^2/(2g) (ft of fluid) and dynamic pressure q = 1/2 rho V^2, both scaling with V^2. Water at 10 ft/s -> 1.55 ft head, 0.67 psi; at 20 ft/s -> 6.21 ft, 2.69 psi (four times for double the velocity). Why a small velocity increase drives large minor losses. The code velocity limits govern.
Formula and source
h_v = V^2 / (2 g) (g = 32.2 ft/s^2); q = 1/2 rho V^2 (lb/ft^2); q_psi = q/144.
The velocity-head and dynamic-pressure relations from first-principles fluid mechanics, by name.
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