Concept reference

Total Dynamic Head

C.1Plain-language definition

Total dynamic head (TDH) is not a pump nameplate constant. It is the head the system requires at one flow and one set of levels, pressures, pipe conditions and valve positions. Change any of those and the duty moves. Pump selection therefore needs a TDH envelope or system curves, not one ceremonial design point.

C.2Governing relation or decision logic

Between chosen boundaries, TDH = Δz + Δ[p/(ρg)] + Δ[αV²/(2g)] + hL, in metres or feet of fluid. Between large open reservoirs, pressure and boundary velocity terms often cancel, leaving static lift plus suction, discharge and local losses. “Often” is an assumption to demonstrate, not a term to delete by habit.

C.3The failure to name

Adding all named losses to a static-head value can double-count terms already embedded in boundary conditions. Selecting only maximum flow with normal levels can also miss the true maximum head or the low-head runout/overload condition.

C.4Field review checklist

• State flow, levels, boundary pressures, pipe condition and valve/pump configuration.
• Show one energy equation and one traceable loss schedule.
• Compute the conditions that produce both maximum and minimum TDH.
• Overlay the full duty envelope on manufacturer pump curves.

C.5Where it fits in the course

§2.5 assembles TDH; §5.5 audits it on a profile.