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.
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.
Long-term operation causes wear in:Gears,Pistons and bores,Bushings and seals.
Worn components increase leakage paths, reducing volumetric efficiency.
Elevated oil temperature reduces viscosity, making it easier for fluid to leak through internal gaps.
Result: higher leakage + lower flow.
Oil that is too thin cannot maintain proper sealing between components.
This accelerates leakage and lowers pump efficiency.
Poor machining accuracy or incorrect tolerances cause excessive internal gaps, leading to volumetric loss even in new pumps.
