1. What Is Volumetric Loss?
Volumetric loss refers to the difference between the theoretical flow a hydraulic pump should deliver and the actual flow output.
It is the portion of hydraulic fluid that fails to reach the discharge side due to internal leakage and inefficiencies.
Formula:Volumetric Loss = Theoretical Flow − Actual Flow
A pump with high volumetric loss delivers less flow, less pressure, and lower overall performance.
2. Main Causes of Volumetric Loss
①Internal Leakage (Primary Cause)
Fluid leaks through internal clearances such as:Gear side gaps,Vane tip gaps,Piston-to-cylinder clearanc,Valve plate wear. This reduces actual output flow directly.
②Component Wear and Aging
Long-term operation causes wear in:Gears,Pistons and bores,Bushings and seals.
Worn components increase leakage paths, reducing volumetric efficiency.
③High Oil Temperature
Elevated oil temperature reduces viscosity, making it easier for fluid to leak through internal gaps.
Result: higher leakage + lower flow.
④Low Oil Viscosity or Incorrect Fluid Selection
Oil that is too thin cannot maintain proper sealing between components.
This accelerates leakage and lowers pump efficiency.
⑤Improper Clearances or Manufacturing Defects
Poor machining accuracy or incorrect tolerances cause excessive internal gaps, leading to volumetric loss even in new pumps.