Hydraulic System Efficiency

Overall system efficiency is the ratio of useful output power to input power. In hydraulic systems, energy is lost at each component as fluid power is converted to mechanical work.

Overall Efficiency = Output Power / Input Power x 100%

Or expressed as component efficiencies multiplied together:

System Eff = Pump Eff x Valve Eff x Line Eff x Actuator Eff

Component Efficiency Breakdown

Pump Efficiency (80-95%): Combines volumetric efficiency (internal leakage) and mechanical efficiency (friction losses). Variable displacement pumps at partial stroke have lower volumetric efficiency.

Valve Losses (85-98%): Pressure drops across directional valves, proportional valves, and flow controls convert hydraulic energy to heat. Proportional and servo systems with throttling control can have significant valve losses.

Line Losses (90-98%): Friction in hoses, tubes, and fittings causes pressure drop. Undersized lines dramatically increase losses. Line loss varies with flow rate squared.

Actuator Efficiency (90-98%): Cylinders lose efficiency to seal friction and internal leakage. Hydraulic motors have both volumetric and mechanical losses similar to pumps.

Power Calculations

Hydraulic power can be calculated from pressure and flow:

Power (HP) = Pressure (PSI) x Flow (GPM) / 1714

Power (kW) = Pressure (bar) x Flow (L/min) / 600

Mechanical output power from a cylinder:

Power (HP) = Force (lbs) x Velocity (ft/min) / 33,000

Typical System Efficiencies

Sankey Diagram Concept

A Sankey diagram visualizes energy flow through a system. The width of each flow represents the amount of power. Branches show where power is lost as heat at each component, with the remaining flow representing useful output.