Velocity Head and Dynamic Pressure
The pressure a moving fluid carries by virtue of its speed alone.
Example
You enter
- Flow velocity (ft/s) 10
- Fluid density (slug/ft³, 1.94 water) 1.94
You get
- Velocity head 1.55 ft of fluid
- Q (psi) 0.674
Checked against published worked examples from: US Bureau of Reclamation.
Details, formula, and sources
ScopeVelocity 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 or tableh_v = V^2 / (2 g) (g = 32.2 ft/s^2); q = 1/2 rho V^2 (lb/ft^2); q_psi = q/144.
Source and editionThe velocity-head and dynamic-pressure relations from first-principles fluid mechanics, by name.
Free accessVelocity head and dynamic pressure are standard fluid-mechanics relations. The code velocity limits and the engineer of record govern.
What governsEstimate. AHJ and licensed professional govern.
API field namesV_fps, rho, h_v_ft, q_psi
- Velocity head h_v = V^2/(2g), g = 32.2 ft/s^2fluid mechanics
- Dynamic pressure q = 1/2 rho V^2; water rho 1.94 slug/ft^3fluid mechanics
- V-squared law both scale with V^2; a small velocity rise drives large minor lossesscope of this tile