ENGINEERING TOOL
Head loss
Pipe head loss is calculated with Darcy-Weisbach, hf = f · (L/D) · v²/(2g), using a friction factor suitable for the fluid and flow regime. Hazen-Williams is an empirical correlation for water only, and the localized loss in fittings is h = ΣK · v²/(2g). Here are the formulas and reference roughness by material.
At a glance
- Head loss is the energy lost to friction in flow, in meters of head. It splits into distributed (straight pipe) and localized (fittings).
- Darcy-Weisbach relates head loss and friction factor. Hazen-Williams is a water correlation; confirm the method application conditions.
- Suction losses reduce available NPSH. Assess piping, fittings, filters and liquid conditions along with the pump curve.
- Provide internal pipe diameters and nozzles separately. For FBCN, check dimensions in the model drawing before specifying reducers and connections.
Updated
Answers to guide your selection
How do I request the head loss calculation?
Send flow, fluid, temperature, internal diameter, length and material for each segment. Include bends, valves, filters and their identification. Layout and operating conditions allow engineering to define calculation assumptions and references.
Which method: Darcy-Weisbach or Hazen-Williams?
The method must fit the fluid, flow regime and project requirements. Darcy-Weisbach uses a friction factor suitable for the assessed condition. Hazen-Williams is a water correlation; do not automatically transfer its coefficients to other fluids.
Data for assessing head loss
Use the information below to start the assessment with the technical team.
Discuss your duty point with engineering
See which piping and fluid data are used in head-loss assessment. Discuss the layout, fittings and duty point with FB Bombas engineering.
Selection depends on process conditions and confirmed data. The assessment and supply scope will be defined with the technical team.
Information for the assessment
- Fluid and temperature (if viscous, state the viscosity in cSt)
- Operating flow (m³/h)
- Internal diameter and pipe material
- Straight length of the run and elevation change
- List of fittings (bends, valves, tees, strainer…)
- Line: suction, discharge or both
The head loss formulas
Total loss combines pipe friction and fitting losses. Equations must use assumptions, properties and coefficients appropriate to the fluid, flow regime and installation.
h_f = f · (L/D) · v²/(2g)Obtain the friction factor using a method suitable for the fluid and flow regime.
h = 10,67 · L · Q^1,852 / (C^1,852 · D^4,87)Q in m³/s, D and L in m. Empirical, no viscosity. Water at ordinary temperature only.
h = ΣK · v²/(2g)Before adding K coefficients, confirm the same velocity and diameter basis. Use data for the fitting and its operating position.
Reference roughness
The Hydraulic Institute publishes these example absolute-roughness values for clean materials. They do not establish the condition of your piping: provide lining, age and internal condition. Design coefficients need an identified reference and conditions.
| Material | Roughness ε (mm) |
|---|---|
| PVC / plastic | 0.00152 |
| Stainless steel | 0.015 |
| Commercial steel (new) | 0.0457 |
| Galvanized steel | 0.152 |
| Asphalted cast iron | 0.122 |
| Cast iron | 0.26 |
| Concrete | 0.305–3.05 |
Localized loss K coefficients
The K coefficient depends on the fitting and flow conditions. Identify the components so their applicable curves or documentation can be consulted.
| Fitting | Data to check |
|---|---|
| Valves | Type, size, opening position and manufacturer data |
| Bends and tees | Geometry, radius, diameter and flow direction |
| Filters and reducers | Model, dimensions and applicable loss curve |
Assessing the pumping line
Velocity depends on flow and internal pipe area. Assess each segment and duty; the pump nozzle diameter alone does not determine the diameter of the entire piping system.
| Line | Condition | What to assess |
|---|---|---|
| Suction | Actual fluid and temperature | Losses, levels, pressure and NPSH margin |
| Discharge | Flow range and configuration | Losses, required pressure and line conditions |
Suction head loss goes straight into the NPSH available formula. Request both calculations in the same conversation and check the margin against cavitation.
Prepare NPSH dataFrequently Asked Questions
What is head loss in piping?
Head loss is the energy a fluid loses as it flows through piping, from friction with the pipe walls and from disturbances at bends, valves, and reducers. It is measured in meters of liquid column. It splits into distributed loss (along the straight pipe) and localized loss (at the fittings). It is unavoidable — there is no frictionless piping — but it is minimized with correct diameter and routing design.
How is head loss calculated?
Darcy-Weisbach relates length, internal diameter, velocity and friction factor: hf = f · (L/D) · v²/(2g). Obtain the factor for the assessed fluid and flow regime. For fittings, use h = K · v²/(2g), with velocity corresponding to each coefficient reference diameter. Add segment losses to obtain the total.
What is the difference between Darcy-Weisbach and Hazen-Williams?
Darcy-Weisbach relates pipe loss, geometry, velocity and friction factor. That factor must represent the fluid and flow regime being assessed. Hazen-Williams is an empirical correlation used for water within its method conditions. Engineering must select assumptions and references appropriate to the process.
What is the recommended maximum velocity at a pump suction?
Design velocity depends on fluid, viscosity, diameter, head loss and pump requirements. Check manual guidance and suction margin at the duty point. A velocity limit alone does not establish that suction has been sized correctly.
How does head loss affect NPSH and cavitation?
Suction head loss reduces available NPSH. Assess piping, fittings and filters with the actual fluid across the flow range. The margin above the pump required criterion must be defined for the duty; NPSH3 does not represent zero cavitation.
What is the roughness of the pipes most used in pumping?
Roughness depends on material, lining and internal condition. The Hydraulic Institute table gives examples for clean materials, not measurements of the installation. Identify piping and service condition before selecting a calculation reference; new-material values do not automatically describe scaled piping.
Hydraulic Institute: table 3.A.1, clean materials
Hydraulic Institute: fitting losses
Assessment depends on installation data, the curve and requested scope. Confirm conditions in the technical proposal. For fire systems, documentation must meet the project and standards and requirements applicable to the location.
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