BIZOMAT MAKEOS · Hydraulics
Pumping System Design (Head, Power and NPSH)
What head and power does this pumping duty need, and will the pump have enough suction head?
Design of a simple pumping system: pipe velocity, Reynolds number and Darcy friction factor (Colebrook–White), friction and fitting losses, total head from static lift, pressure difference and losses, hydraulic, shaft and motor power, and net positive suction head available from the suction conditions compared with the pump’s requirement.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Duty | ||
| Flow | L/min | Flow rate at the duty point. |
| Static lift (outlet level − suction level) | m | Height difference between the delivery and suction liquid levels. |
| Outlet pressure − suction pressure | bar | Pressure on the delivery surface minus pressure on the suction surface. |
| Discharge and suction pipe | ||
| Pipe bore | mm | Internal diameter of the pipe (suction pipe assumed the same size). |
| Total pipe length | m | Total length of pipe including suction. |
| Total fitting loss coefficient | Sum of fitting and valve loss coefficients, including entry and exit. | |
| Pipe roughness | mm | Absolute roughness of the pipe (0.045 mm commercial steel). |
| Fluid | ||
| Density | kg/m³ | Liquid density. |
| Kinematic viscosity | mm²/s | Kinematic viscosity (1 mm²/s for water at 20 °C). |
| Suction | ||
| Absolute pressure on the suction surface | bar | Absolute pressure on the suction liquid surface (atmospheric for an open tank). |
| Vapour pressure at the pumping temperature | bar | Vapour pressure of the liquid at the pumping temperature. |
| Suction surface above the pump (negative if below) | m | Height of the suction surface above the pump centre line. |
| Suction pipe length | m | Length of the suction line. |
| Suction fitting loss coefficient | Fitting losses in the suction line. | |
| NPSH required by the pump | m | NPSH the pump needs at this flow (from its curve). |
| Machine | ||
| Pump efficiency | % | Pump efficiency at the duty point. |
| Motor margin | % | Margin above shaft power for the motor. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Duty
What this means: Flow
- What it is
- Volume of liquid the pump must deliver per unit time at its duty point, the flow the process needs.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 10000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Velocity rises with flow and friction losses roughly with its square.
- Get it right
- 1 m³/h equals 16.67 L/min; check the unit of your process data.
What this means: Static lift (outlet level − suction level)
- What it is
- Vertical height from the liquid surface on the suction side to the liquid surface or outlet point on the delivery side.
- Units and format
- Enter a number in m: metres. The form accepts -1000 m to 5000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Adds metre for metre to the total head.
- Get it right
- Measure between liquid levels, not pump connections; enter a negative value if delivery is lower than suction.
What this means: Outlet pressure − suction pressure
- What it is
- Pressure on the delivery liquid surface minus pressure on the suction surface, for example a pressurised vessel at the outlet.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts -100 bar to 1000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Converted to head as Δp ÷ ρg and added to the total head.
- Get it right
- Use 0 for two open tanks; both pressures must be on the same basis (both gauge or both absolute).
Discharge and suction pipe
What this means: Pipe bore
- What it is
- Internal diameter of the pipe. The tool assumes the suction pipe has the same bore.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Losses fall steeply as the bore increases.
- Get it right
- Use the actual internal bore for the pipe schedule, not the nominal size.
What this means: Total pipe length
- What it is
- Total length of pipe the liquid flows through, suction and delivery together, used for the friction head.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 1000000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pipe friction loss rises in proportion to length.
- Get it right
- Include the suction length here as well; the separate suction length is only for the NPSH check.
What this means: Total fitting loss coefficient
- What it is
- Sum of the loss coefficients of every fitting and valve in the whole line, including pipe entry and exit.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 1000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fitting losses rise in proportion to the sum.
- Get it right
- Add the K values of all bends, valves, tees, entry and exit, suction side included.
What this means: Pipe roughness
- What it is
- Absolute roughness of the pipe’s inner wall, the average height of its surface irregularities, used in the friction factor.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.045 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Rougher pipe raises the friction factor in turbulent flow.
- Get it right
- Enter millimetres from pipe data; old or scaled pipe is rougher than new.
Fluid
What this means: Density
- What it is
- Density of the pumped liquid at the pumping temperature.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 20000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A denser liquid needs more power for the same head, and the pressure difference converts to less head.
- Get it right
- Use the value at operating temperature from the fluid data sheet.
What this means: Kinematic viscosity
- What it is
- Kinematic viscosity of the liquid at the pumping temperature (dynamic viscosity ÷ density). It sets the Reynolds number.
- Units and format
- Enter a number in mm²/s: mm²/s. The form accepts 0.000001 mm²/s to 1000000 mm²/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 mm²/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Thicker liquids give a lower Reynolds number and usually higher friction.
- Get it right
- mm²/s equals centistokes; do not enter dynamic viscosity in mPa·s.
Suction
What this means: Absolute pressure on the suction surface
- What it is
- Absolute pressure acting on the liquid surface on the suction side, atmospheric for an open tank.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0 bar to 100 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.013 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher suction pressure raises NPSH available.
- Get it right
- This is absolute pressure, not gauge: an open tank is at atmospheric pressure, not 0.
What this means: Vapour pressure at the pumping temperature
- What it is
- Absolute pressure at which the liquid boils at the pumping temperature. Below this the liquid flashes to vapour and the pump cavitates.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0 bar to 100 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.023 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher vapour pressure lowers NPSH available.
- Get it right
- Take it from steam or fluid tables at the actual temperature; it rises steeply as liquid warms.
What this means: Suction surface above the pump (negative if bel…
- What it is
- Height of the suction liquid surface above the pump centre line. Negative when the pump lifts from a sump below it.
- Units and format
- Enter a number in m: metres. The form accepts -50 m to 500 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with -2 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Adds metre for metre to NPSH available.
- Get it right
- Measure to the pump impeller centre line, and use the lowest expected liquid level.
What this means: Suction pipe length
- What it is
- Length of the suction pipe from the tank to the pump inlet, used only for the suction losses in the NPSH check.
- Units and format
- Enter a number in m: metres. The form accepts 0 m to 100000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Longer suction lines lower NPSH available.
- Get it right
- This is part of the total pipe length, not extra to it.
What this means: Suction fitting loss coefficient
- What it is
- Sum of the loss coefficients of the fittings on the suction side only, including the pipe entry, used for the NPSH check.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 1000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher suction losses lower NPSH available.
- Get it right
- These fittings should also be included in the total loss coefficient.
What this means: NPSH required by the pump
- What it is
- Net positive suction head the pump needs at the duty flow to avoid harmful cavitation, read from the pump maker’s curve.
- Units and format
- Enter a number in m: metres. The form accepts 0 m to 100 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Read it at your duty flow; it rises with flow.
Machine
What this means: Pump efficiency
- What it is
- Pump efficiency at the duty point: hydraulic power delivered to the liquid divided by power at the pump shaft.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 70% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shaft and motor power rise as efficiency falls.
- Get it right
- Read it from the pump curve at your duty flow; type the percentage.
What this means: Motor margin
- What it is
- Extra motor power above the calculated shaft power, to cover operation away from the duty point, wear and fluid changes.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Motor size rises in proportion to 1 + margin.
- Get it right
- Type a percentage of shaft power; your standards or the pump maker set it.
Method and formulas
- v = Q ÷ A; Re = v d ÷ ν; f from Colebrook–White (64 ÷ Re if laminar).
- Losses h_f = (f L ÷ d + ΣK) v² ÷ 2g; total head H = Δz + Δp ÷ ρg + h_f.
- Hydraulic power = ρ g Q H; shaft power = hydraulic ÷ η; motor = shaft × (1 + margin).
- NPSH_a = (p_s − p_v) ÷ ρg + z_s − suction losses.
- Example: 300 L/min through 80 m of 50 mm pipe needs 28.936 m of head and a 2.331 kW motor.
Limitations
- Single pipe size and steady flow; branched systems need a network calculation.
- Pump efficiency and NPSH required come from the pump curve at the duty flow.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Specify a pump duty point and motor size
- Check whether a suction arrangement will cavitate
- Choose a pipe size by velocity and running cost
Who it is for
- Process engineers
- Maintenance engineers
- Hydraulic engineers
What you get
- Velocity, friction factor and losses
- Total head, power and motor size
- NPSH available against required
Interpreting the result
- If NPSH margin is short, raise the suction level, shorten the suction line or enlarge its bore.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3021–3026, 3036. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
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Method explained here · BIZOMAT original book
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