Total Dynamic Head Calculator
Pump-selection TDH from the three components: static lift, Hazen-Williams pipe friction, and fitting minor losses. Enter flow, pipe geometry, C-factor, and ΣK; the calculator returns each component, the total, and a velocity check against the 2–8 ft/s force-main range.
Static head is the elevation difference between the pumping water level and the discharge point (use the wet-well low level for the conservative TDH case). Hazen-Williams applies to water at ordinary temperatures in turbulent flow; for other fluids use Darcy-Weisbach. In SI, friction uses hf = 10.67·L·Q1.852/(C1.852·D4.87) with Q in m³/s and D in m.
Hazen-Williams C for common force-main materials
| Pipe material | C (new) | C (design/aged) |
|---|---|---|
| PVC / HDPE | 150–155 | 150 |
| Ductile iron, cement-mortar lined | 140–150 | 140 |
| Steel, new welded | 140–145 | 130 |
| Cast iron, unlined, 20+ yr | — | 80–110 |
| Concrete / cylinder pipe | 135–140 | 130 |
Worked example
Example — sewage force main
References: Hazen, A. & Williams, G.S. (1920). Hydraulic Tables, 3rd ed. GLUMRB (2014). Recommended Standards for Wastewater Facilities (Ten-State Standards), §48. Sanks, R.L. et al., Pumping Station Design, 3rd ed., Butterworth-Heinemann.
Common mistakes
- Using the high wet-well level for the design point. TDH is largest with the wet well at its pump-off level. Size the pump for that condition and check the run-out point at the high level, where the pump may move more flow than intended.
- Using new-pipe C for a force main. Sewage force mains build up grease and slime. Many designers check at C = 120 for the worst case and C = 140–150 for the run-out case, and pick a pump that works at both.
- Leaving out high points. If the force main crosses a summit above the discharge, the static head is set by that high point, and air release valves are needed there.
- Confusing water horsepower with motor size. WHP divided by pump efficiency gives brake horsepower. Motor selection also needs a service factor and the full pump curve, not just one duty point.
When this calculator doesn’t apply
Hazen-Williams assumes water at ordinary temperature in turbulent flow. Sludge, slurries and fluids other than water need Darcy-Weisbach with appropriate properties. This tool gives a single duty point. Pump selection needs the system curve across the full range of wet-well levels and pipe conditions, plotted against the manufacturer’s pump curves, and an NPSH check on the suction side.
Related tools
- Minor loss calculator — itemize the fittings behind ΣK
- Hazen-Williams — the friction component alone
- Pump BHP — brake and motor horsepower from Q and TDH
- Pump affinity laws — how TDH and power move when you change speed or impeller diameter
- Lift station sizing — wet well volume and pump cycle time
- Darcy-Weisbach — friction loss for non-water fluids or laminar flow