Calculate The Power Required To Generate Hydraulic Pump Flow

The role of a hydraulic pump is to generate flow and provide enough pressure to overcome system resistance. To choose a suitable pump and size the drive correctly, you need to understand the system’s required operating pressure, pump flow rate, and efficiency.

What does a hydraulic pump do?

A hydraulic pump moves fluid through a system at a required flow rate and supplies sufficient pressure to overcome the operating resistance of the circuit (loads, valves, line losses, and elevation/differential height if relevant). To ensure you have a suitable pump, you’ll typically calculate the operating pressure the system needs to reach and the flow required to achieve the desired actuator speed.

Tip

Flow mainly affects speed (how fast cylinders/motors move), while pressure mainly affects force/torque. Both matter when sizing a hydraulic pump.

Hydraulic pump efficiency: the 3 key types

There are three categories of efficiency to consider when looking at hydraulic pumps and their pump flow rates:

1) Volumetric efficiency

Volumetric efficiency compares the actual flow delivered at a given pressure to the theoretical flow. Theoretical flow is calculated by multiplying a pump’s displacement per revolution by its driven speed.

Example

If a hydraulic pump has a displacement of 100 cc/rev and is driven at 1000 rpm, its theoretical flow is 100 L/min.

2) Mechanical / hydraulic efficiency

Mechanical (hydraulic) efficiency compares the theoretical torque required to drive the pump to the actual torque required. In a perfect world, a pump delivering flow at zero pressure would require no torque to turn—real pumps have friction and internal losses, so the actual torque is higher.

3) Overall efficiency

Overall efficiency is the product of volumetric and mechanical/hydraulic efficiency. It’s commonly used to estimate the drive power required by a hydraulic pump at a given flow and pressure.