Calculator Inputs
Formula Used
Total Dynamic Head sums the energy rise required to move fluid between two points:
- z: elevation head (m)
- P: pressure (Pa); converted from kPa input
- V: velocity (m/s), computed from flow and diameter
- hf: friction head (m), from Darcy–Weisbach or Hazen–Williams
- hm: minor-loss head (m) using ΣK·V²/(2g)
How to Use
- Enter flow rate and choose its unit.
- Provide pipe diameter and length for the main run.
- Enter elevations and any gauge pressures at both points.
- Add ΣK for fittings, valves, and entrances/exits.
- Select a friction method, then compute TDH.
- Download CSV or PDF for submittals and logs.
Example Data Table
| Scenario | Flow (m³/h) | Diameter (mm) | Length (m) | Δz (m) | ΣK | Method | Typical TDH (m) |
|---|---|---|---|---|---|---|---|
| Temporary dewatering line | 25 | 100 | 80 | 12 | 4 | Darcy | ~18–24 |
| Concrete washout transfer | 10 | 75 | 60 | 6 | 6 | Darcy | ~10–16 |
| Site water distribution | 40 | 150 | 200 | 8 | 3 | Hazen | ~12–20 |
Example values illustrate typical ranges; verify with project data.
Professional Notes on Total Dynamic Head
1) Why TDH matters on construction sites
Total dynamic head is the practical measure of how hard a pump must work to move water through a temporary or permanent system. It combines elevation difference, pressure requirements, flow velocity effects, and all losses in the piping. Getting TDH right prevents undersized pumps, unstable flow, excessive energy use, and delays during dewatering, washdown, testing, and commissioning.
2) Break the problem into head components
Start with static head (z₂ − z₁). Add pressure head if you must deliver to a pressurized header, tank, or spray system. Include velocity head change when suction and discharge diameters differ. Then capture friction losses along straight runs and minor losses from fittings, valves, strainers, entrances, and exits. Finally, add any safety margin or special device head.
3) Choosing a friction method
Darcy–Weisbach is broadly applicable and works for many fluids and pipe materials when density and viscosity are known. Hazen–Williams is common for water distribution and is convenient when you use a C value from specifications. For mixed systems, you can override friction using a known head loss from vendor curves or prior site measurements.
4) Interpreting the result for pump selection
TDH represents the head the pump must overcome at the chosen flow. Use the TDH and flow pair to read the pump curve, then verify the duty point is near a stable and efficient region. Confirm the pump can handle expected solids, startup conditions, and any elevation or routing changes during the work.
5) Example data and expected outcome
The following example shows typical inputs for a temporary transfer line. Values are illustrative and should be replaced with project measurements.
| Input | Example value | Notes |
|---|---|---|
| Flow | 30 m³/h | Moderate site distribution flow |
| Main pipe | 150 mm ID, 120 m | Straight run excluding fittings |
| Elevation change | z₂ − z₁ = 18 m | Lift from sump to discharge point |
| Fittings | ΣK = 3.5 | Bends, valve, entrance, exit |
| Method | Darcy–Weisbach | Uses density and viscosity inputs |
After computing TDH, document the duty point, confirm NPSH requirements, and keep a record of any changes to routing or valve positions. That record helps troubleshooting and supports submittals, handover, and repeatable operations.
FAQs
1) What is the difference between static head and TDH?
Static head is only elevation difference. TDH adds pressure requirements, velocity changes, friction losses, and minor losses. TDH is the realistic head the pump must overcome at a specific flow.
2) When should I use Hazen–Williams instead of Darcy–Weisbach?
Use Hazen–Williams for water flow in typical distribution piping when a reliable C value is available. Use Darcy–Weisbach when fluid properties vary, roughness matters, or the system includes non-water fluids.
3) How do I estimate ΣK for fittings?
Sum published K values for each fitting and valve in the line, including entrance and exit. If detailed K values are unknown, use conservative allowances and refine later with vendor data or measured pressure drops.
4) Why does pipe diameter strongly affect TDH?
Smaller diameter increases velocity, which increases friction losses and minor losses. Because friction depends on velocity and diameter, even modest diameter changes can significantly shift TDH at the same flow.
5) Can I enter negative elevation difference?
Yes. If the discharge point is lower than the suction point, static head becomes negative and reduces TDH. Still include friction and minor losses, and check for minimum pressure needs at the discharge location.
6) What does the Reynolds number tell me?
Reynolds number indicates flow regime. Low values suggest laminar flow, while high values indicate turbulent flow. The friction factor estimate depends on this regime and affects the calculated friction head.
7) How should I add a safety margin?
Use “Additional head” to include filters, meters, unknown fittings, and operational uncertainty. Many teams add a modest margin, then validate performance during commissioning and adjust inputs based on measured pressures and flow.
Use this tool to select pumps with confidence today.