Static Head

Definition

Static head is the pressure head contributed by elevation alone — with no fluid motion and no velocity component. For a liquid column of height h and density ρ, the static pressure at the base is P = ρg·h. Expressed as a head (metres or feet of liquid), this is simply h.

Static head is distinct from two closely related quantities:

• Stagnation pressure (total head): static pressure plus the velocity head (½ρv²). At a pipe discharging freely to atmosphere, the static pressure at the open end is atmospheric; the stagnation pressure also carries the velocity head. Reading the wrong one into a hand calculation is a frequent source of error.
• Total dynamic head (TDH): the total head a pump must deliver for a given duty — static head plus friction and fitting losses plus any velocity and pressure-head differences between the supply and delivery points.

The net static head (or net static lift) is the elevation difference measured between the two free surfaces (or boundary points) that actually bound the flow path — not between arbitrary nodes mid-route.

Engineering context

In any gravity-driven or elevation-influenced system, static head is the energy the fluid either gains (downhill) or must overcome (uphill) purely by virtue of its position. This appears in three common situations:

• Gravity-fed systems: an elevated tank drives flow through a pipe network without a pump. The available static head equals the difference between the liquid surface elevation and the outlet elevation, adjusted for the surface pressure at each end.
• Pump suction: the static head of the supply contributes to NPSH available. A low tank level or long suction line reduces the available static head and increases cavitation risk.
• Tank or vessel boundaries: in a network model, the effective boundary pressure at a tank or reservoir is the surface pressure plus the static head from the free surface to the connection point. Setting the elevation or liquid level incorrectly means every downstream result inherits the error — see Tank and Vessel Boundaries.

The most common calculation error is measuring net static head from the pipe inlet connection rather than from the free surface above it, missing the liquid column contribution inside the tank. For shallow tanks the error is small; for tall tanks it is significant. The correct approach is described in Static Head and TDH: Calculating Flow in Gravity-Driven Pipe Systems.

Related definitions

Darcy-Weisbach equation · NPSH · System curve · Stagnation pressure · Elevation · HGL (hydraulic grade line)

See it in FluidFlow

FluidFlow’s Tank or Vessel Reservoir and Atmospheric Ends boundaries incorporate static head automatically when elevation and liquid surface level are set correctly — the solver uses surface pressure plus ρg·h as the effective boundary pressure. The Stagnation Pressure model is recommended for boundaries where static head dominates (large tanks, atmospheric inlets and outlets), because it correctly represents the pressure at a point where velocity is negligible. See the Static Head and TDH workflow for the full modelling sequence.