Hydraulic Power: Measurement and Determination Explained Clearly

Hydraulic power is a physical value from which the load capacity of hydraulic systems can be determined. This metric is primarily required for the design of the hydraulic pump. The unit of measurement is the kilowatt.

Measurement of Hydraulic ‘Power’

• ‘Power’ is a composite quantity of the third degree and
  is fundamentally defined by ‘work per unit time’.
• ‘Work’, in turn, is a derived quantity from the derived quantity ‘force’ multiplied by the base quantity ‘distance’.
• ‘Force’ itself is determined from the base quantities ‘mass’ and ‘acceleration’.

Therefore, several preliminary calculations are necessary to determine ‘power’.

Specifics of Hydraulic Power

To calculate hydraulic power, the base quantities are thus transferred to the specific characteristics of hydraulics.

The volume flow is the amount of hydraulic fluid that passes through a defined cross-sectional area within a defined time. The unit of measurement for volume flow is ‘liters per minute’.

Translated, the power indicates how the pressure within a hydraulic system decreases.
The more resistances and consumers connected in a hydraulic system, the lower the power of the overall system. This means that the more consumers and resistances are to be connected in a hydraulic system, the higher the system’s power must be designed.

The determination of the required hydraulic power thus allows conclusions to be drawn about the necessary design, drive, and performance of the hydraulic pump. The power of a hydraulic pump is determined by its construction and its drive.

For a volume flow of Q = 1 liter per minute to reach an operating pressure of p = 500 bar, a drive power of approximately 1 kilowatt is required. Correspondingly higher volume flows or operating pressures can be roughly estimated to obtain initial indications for the design of the hydraulic system.

Prerequisites for Successful Designs

This explains why the precise calculation of a hydraulic system is of utmost importance: hoses and pipes cause friction losses, which lead to a loss of hydraulic power. Bends and branches cause turbulence, which in turn costs power. Orifices and sharp transitions, e.g., at valves, are also consumers of hydraulic power.

At the same time, the pressure in a hydraulic system cannot be increased indefinitely. The pressures prevailing in hydraulic systems can amount to several hundred bar. If these high pressures meet fast volume flows that also flow over sharp transitions, the dreaded effect of cavitation quickly occurs. Cavitation always means a creeping, internal destruction of the hydraulic system. This effect can be delayed or ideally completely prevented by precise design of pressure, power, and volume flow.

Determining Hydraulic Power

Hydraulic power can only be calculated in advance to a certain extent. The more complex a hydraulic system becomes, the more difficult it is to account for all power-consuming factors. Therefore, the design of a hydraulic system always includes determining the actual hydraulic power after its commissioning. This can be achieved by simply determining the pressure difference before and after the hydraulic pump.

The efficiency of a hydraulic system is determined in the same way. Hydraulic power and efficiency are therefore directly related.