Tools & selection knowledge
Hydraulic Pump Calculator
Calculate hydraulic pump flow, displacement, speed and mechanical drive power. Use the calculator, review a worked example and send your operating point for selection.
IMPEX ENGINEERING TOOLS
Size the pump. Know the power.
Calculate hydraulic pump flow, displacement, speed and drive power. Turn your operating point into a clear selection enquiry.
01 / Your operating point
Enter the pump displacement and shaft speed to calculate delivered flow and the power needed at your pressure.
Outlet minus inlet pressure. For low-pressure tank suction, outlet gauge pressure is usually a close approximation.
Mechanical output at the drive shaft, not electrical input power.
Efficiency & drive reserve
Applied only to the preliminary motor rating. Calculated pump power stays unchanged.
Defaults: ηv = 92%, ηhm = 90%. These are editable assumptions, not manufacturer performance data. Use values for your operating point.
Explore pump types
Fixed or variable displacement · use effective Vg
02 / Calculated results
| Pump displacement | — |
|---|---|
| Delivered flow | — |
| Shaft speed | — |
| Hydraulic output power | — |
| Required shaft torque | — |
| Estimated pump power loss | — |
| Overall pump efficiency | — |
| Theoretical flow (no leakage) | — |
Next listed metric rating above shaft power + reserve. Confirm starting torque, duty and motor data before selection.
Calculated at full available shaft power. Allow a reserve or reduce the operating point for actual selection.
Shaft power vs. pressure difference
Calculated trend from 0 to your Δp, with fixed displacement, speed and efficiencies. Not a manufacturer performance curve.
Preliminary steady-state calculation. It does not verify a specific pump model or replace manufacturer curves and engineering selection. Pump power loss is not a complete system cooling calculation. No allowance for acceleration, cold starts or pressure transients is included.
Flow · displacement · speed · drive power
How to calculate hydraulic pump flow and power
This hydraulic pump calculator covers positive-displacement pumps for hydraulic oil. Calculate delivered flow from displacement and speed, find the displacement needed for a target flow, determine shaft speed, or calculate the maximum flow available from a mechanical drive-power limit.
The pump calculator is also available in our hydraulic pump catalogue.
Hydraulic pump formulas and units
Vg = 1000 × Q / (n × ηv)
n = 1000 × Q / (Vg × ηv)
P hydraulic = Δp × Q / 600
P shaft = P hydraulic / (ηv × ηhm)
T shaft = Δp × Vg / (20π × ηhm)
| Symbol | Meaning | Metric unit |
|---|---|---|
| Vg | Effective pump displacement | cm³/rev |
| n | Pump shaft speed | rpm |
| Q | Delivered flow | l/min |
| Δp | Outlet minus inlet pressure | bar |
| ηv / ηhm | Volumetric / hydromechanical efficiency | Fractions in formulas; % in calculator |
| P / T | Power / torque | kW / N·m |
Worked example: 32 cm³/rev pump at 1450 rpm
At a pressure difference of 160 bar, with assumed volumetric efficiency of 92% and hydromechanical efficiency of 90%, a 32 cm³/rev pump running at 1450 rpm delivers approximately 42.69 l/min. Hydraulic output power is 11.38 kW, required pump shaft power is 13.75 kW, and shaft torque is 90.54 N·m.
These efficiencies are example assumptions. The calculator allows you to change them. A 10% drive reserve gives approximately 15.12 kW before rounding up to the next listed metric motor rating. Actual motor selection also requires starting-torque and duty checks.
What to check before selecting a pump
Confirm continuous pressure and speed ratings, rotation, mounting flange, shaft, port positions, fluid compatibility, viscosity and inlet conditions. For variable-displacement pumps, use the effective displacement at the operating point and specify the required control. Maximum displacement alone does not determine regulated flow.
Does the calculator include pump efficiency?
Yes. Volumetric efficiency reduces delivered flow. Hydromechanical efficiency increases required shaft torque. Their product is overall pump efficiency. Use manufacturer values for the actual operating point when available.
Is shaft power the same as electrical input power?
No. Shaft power is the mechanical power delivered to the pump. Electrical input power is higher because the electric motor and any drive have losses. Their efficiencies are not included here.
Can I use the result to choose a specific pump model?
The result defines an operating point. Model suitability still depends on the manufacturer’s ratings, controls, interfaces and operating conditions. Send the calculation to request a pump selection.
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