{"id":3408,"date":"2026-07-14T22:45:27","date_gmt":"2026-07-14T14:45:27","guid":{"rendered":"https:\/\/prancehydraulic.com\/blog\/hydraulic-pump-flow-calculation\/"},"modified":"2026-07-17T15:58:30","modified_gmt":"2026-07-17T07:58:30","slug":"hydraulic-pump-flow-calculation","status":"publish","type":"post","link":"https:\/\/prancehydraulic.com\/es\/blog\/hydraulic-pump-flow-calculation\/","title":{"rendered":"How to Calculate Hydraulic Pump Flow From Displacement and Speed"},"content":{"rendered":"

Hydraulic pump flow calculation is direct:<\/strong> for a positive-displacement pump, theoretical flow in litres per minute is Q = (Vg \u00d7 n) \/ 1000<\/strong>, where Vg is cm\u00b3\/rev and n is rpm. Use this result to set the required displacement-speed combination, then verify delivered flow, inlet conditions and operating limits against the selected model’s datasheet.<\/p>\n

\"Hydraulic<\/p>\n

Part 1. What is the hydraulic pump flow calculation?<\/h2>\n

A positive-displacement pump moves a nominal volume during each shaft revolution. Multiply displacement by revolutions per minute to obtain the theoretical volume moved per minute. Displacement and drive speed are therefore the first two inputs in every pump-flow calculation.<\/p>\n

Pressure does not replace the flow calculation. The pump supplies flow; circuit resistance creates pressure. A pump that meets the theoretical flow requirement is still unacceptable when its permitted speed, inlet condition, pressure or fluid requirements are outside the documented range.<\/p>\n

Part 2. Which units belong in the formula?<\/h2>\n

Use one unit system throughout the calculation.<\/p>\n\n\n\n\n\n\n\n
Required result<\/th>\nFormula<\/th>\nInputs<\/th>\n<\/tr>\n<\/thead>\n
Theoretical flow, L\/min<\/td>\nQ = (Vg \u00d7 n) \/ 1000<\/code><\/td>\nVg in cm\u00b3\/rev; n in rpm<\/td>\n<\/tr>\n
Theoretical flow, US gal\/min<\/td>\nQ = (D \u00d7 n) \/ 231<\/code><\/td>\nD in in\u00b3\/rev; n in rpm<\/td>\n<\/tr>\n
Estimated actual flow<\/td>\nQactual = Qtheoretical \u00d7 \u03b7v<\/code><\/td>\n\u03b7v is volumetric efficiency as a decimal<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The \/1000<\/code> conversion is necessary because 1000 cm\u00b3 equals one litre. Do not mix cm\u00b3\/rev with an imperial denominator, or use engine rpm when a PTO or gearbox changes the pump speed.<\/p>\n

Part 3. Why theoretical flow differs from actual delivered flow<\/h2>\n

Theoretical flow assumes that every displacement chamber fills and discharges its nominal volume. Actual delivered flow falls below that number when internal leakage and other volumetric losses are present. Parker and Danfoss technical literature both make this distinction: displacement and speed establish the theoretical value, while real operating conditions determine delivered flow.<\/p>\n

Volumetric efficiency is not a generic constant to copy into an RFQ. It changes with the specific pump, pressure differential, fluid viscosity, temperature, speed, wear state and control position. Calculate the duty first, then use the selected model’s curve or datasheet to verify actual flow.<\/p>\n

Part 4. Worked example: 50 cm\u00b3\/rev at 1500 rpm<\/h2>\n

For a fixed 50 cm\u00b3\/rev pump driven at 1500 rpm:<\/p>\n

Qtheoretical = (50 \u00d7 1500) \/ 1000 = 75 L\/min<\/code><\/p>\n

If a documented model curve supports a volumetric efficiency of 0.92 at the actual duty point, the estimated delivered flow is:<\/p>\n

Qactual = 75 \u00d7 0.92 = 69 L\/min<\/code><\/p>\n

This calculation establishes a 75 L\/min theoretical requirement, not a universal 69 L\/min result for every 50 cm\u00b3\/rev pump. Apply model-specific efficiency evidence at the relevant pressure, fluid and temperature to confirm delivered flow.<\/p>\n

\"Hydraulic<\/p>\n

Part 5. Which speed, inlet and drive limits can change the result?<\/h2>\n

Pump speed must be the pump shaft speed, not an assumed engine speed. Confirm the engine operating range, PTO or gearbox ratio, coupling ratio and speed changes across the duty cycle. A variable-speed drive changes theoretical flow in direct proportion to speed; a variable-displacement pump changes flow through its displacement setting as well.<\/p>\n

The flow calculation does not override inlet requirements. Inlet pressure, line size, oil viscosity, temperature and reservoir arrangement determine whether the pump can fill correctly. When those conditions cannot support the requested duty, reduce speed, change the inlet arrangement or select a model with documented suitability.<\/p>\n

For the architecture choice behind the calculation, compare piston and vane pump control paths<\/a> y el open-loop variable-displacement pump guide<\/a>.<\/p>\n

Part 6. What should a buyer provide before requesting a pump quote?<\/h2>\n

Send the calculated target flow together with the inputs that make it auditable:<\/p>\n