Fluid Mechanics

Head is the mechanical energy of a liquid per unit weight, expressed as a height of the liquid. The static pressure of a flowing liquid and how a wall tap reads it, pressure head for any specific gravity, stagnation pressure, velocity head from the flow and the pipe bore, and elevation head.

Every pressure value has a zero reference. Absolute, gauge, vacuum, and differential pressure; the pressure of a liquid column; manometric units; density and specific gravity of liquids; atmospheric pressure and site elevation; and how a pressure indicator establishes its reference.