Determine pump flow rate and required motor power. Support for gear, piston, and vane pumps. Calculate theoretical vs. actual flow with efficiency factors.
Pump flow is the volume of fluid a positive-displacement pump delivers per unit time at a given shaft speed and pressure. This calculator multiplies displacement per revolution by RPM and applies volumetric efficiency to yield the actual flow at the outlet, which is what determines actuator speed and cycle time. Use it when matching a pump to a duty cycle, replacing a worn unit, or diagnosing slow cylinder motion.
Theoretical flow Q_t = D × N / 231 for gallons per minute when displacement D is in cubic inches per revolution and N in RPM. SI form is Q_t = D × N / 1000 in liters per minute when D is in cm³/rev. Real-world flow Q = Q_t × η_v where volumetric efficiency η_v ranges from 0.85 for worn gear pumps to 0.97 for fresh piston pumps; efficiency drops with pressure as internal slip increases. The calculator accepts displacement in either cc/rev or cubic-inches/rev, then reports flow in lpm and GPM. Slippage at high pressure can reduce flow by 5–15%, so sizing for actuator speed at maximum load pressure rather than at no-load is critical. Drive horsepower is HP = (P × Q) / (1,714 × η_t) where η_t is total efficiency; this is the second sanity check after the flow result.
A power-unit designer needing 15 GPM at 2,500 psi computes that a 2.4 cubic-inch displacement pump at 1,750 RPM delivers 18.1 GPM theoretical and 17.0 GPM actual, providing comfortable reserve for cooler and pilot flow.
A maintenance engineer cross-checks a vendor-recommended replacement gear pump by entering its 1.6 cc/rev displacement at the existing 2,200 RPM motor speed and confirms the resulting 3.52 lpm matches the original spec.
A technician investigating a cylinder that extends 30% slower than commissioning data measures pump flow with a flow meter, compares it to the calculator output at rated RPM, and isolates the gap to internal pump wear rather than valve fault.
Higher pressure increases internal leakage (slip), reducing real-world flow. Always calculate at your highest expected pressure for accurate cycle-time predictions.
Volumetric efficiency is the ratio of actual flow to theoretical flow, typically 85-97% for hydraulic pumps. It accounts for fluid that leaks past clearances inside the pump.
Common causes are inlet starvation (clogged strainer, low fluid), high working pressure (more slip), worn pump elements, or low oil viscosity at elevated temperature.