KEVOS® MAKEOS · Hydraulics
Pump Suction Line Check (Friction Loss, NPSH Available, Lowest Liquid Level)
Will my pump cavitate with this suction line, how low can the liquid level fall before it does, and is the suction velocity reasonable?
Check of a pump suction line: velocity in the suction pipe against your limit, friction factor and head loss through the pipe, foot valve and fittings (as the pipe friction tool), NPSH available from the surface pressure, vapour pressure, liquid level and suction losses compared with the pump’s NPSH required plus your margin (as the NPSH available tool), and the lowest liquid level that still keeps the margin.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Flow the pump delivers at duty. |
| Suction pipe inside diameter | mm | Inside diameter of the suction pipe. |
| Suction pipe length | m | Length of the suction pipe. |
| Sum of fitting loss coefficients (foot valve, bends) | Sum of loss coefficients for the entry, foot valve, strainer and bends. | |
| Kinematic viscosity | cSt | Kinematic viscosity at the pumping temperature. |
| Liquid density | kg/m³ | Density of the liquid. |
| Pipe roughness | mm | Roughness of the pipe bore. |
| Pressures and levels | ||
| Pressure on the liquid surface (absolute) | kPa | Absolute pressure on the liquid surface (atmospheric for an open sump). |
| Vapour pressure at pumping temperature | kPa | Vapour pressure of the liquid at the pumping temperature. |
| Liquid level above pump centreline (negative = below) | m | Height of the liquid surface above the pump centreline; negative for a suction lift. |
| Pump NPSH required at duty | m | NPSH the pump needs at the duty flow, from its curve. |
| Required margin | m | Extra head you want above the NPSH required. |
| Largest suction velocity | m/s | Largest velocity you accept in the suction pipe. |
Method and formulas
- Velocity = Q ÷ A; head loss h_f = (f L ÷ d + ΣK) v² ÷ 2g with the Colebrook friction factor (as the pipe friction tool).
- NPSH_a = (p_s − p_v) ÷ ρg + z − h_f (as the NPSH available tool); margin = NPSH_a − NPSH_r.
- Lowest level = z − (margin − margin required).
- Example: the suction loses 0.23159 m, NPSH available is 7.8797 m against 3 m required, and the level may fall to -5.8797 m.
Limitations
- Steady flow at the duty point; NPSH required rises at higher flows.
- Entrained air and vortexing at a low submergence are not covered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a pump installation before ordering
- Find how far a sump may be drawn down
- Size a suction pipe
Who it is for
- Plant engineers
- Maintenance engineers
- Pump installers
What you get
- Suction velocity and head loss
- NPSH available and margin
- Lowest liquid level for the margin
Interpreting the result
- Raising the liquid level or shortening the suction line helps more than any change to the pump.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Pump Suction Line Check (Friction Loss, NPSH Available, Lowest Liquid Level) calculator
