FOCUS ON THE OPTIMUM VISCOSITY RANGE

VISCOSITY

Hydraulic Fluid Performance

The viscosity of a hydraulic fluid is a critical element in the transfer of hydraulic power. The ideal viscosity range for a fluid – and thus its highest efficiency – is usually between 10 and 100 mm²/s, depending on the application.


If a hydraulic fluid is too thin this leads to increased wear, lower power transmission, lower volumetric efficiency and overheating. A fluid of too high a viscosity leads to a loss of power, decreased mechanical efficiency, and in the worst cases, cavitation and mechanical failure.
 

The widened Temperature Operating Window

The diagram shows the viscosity of two fluids plotted across a range of operating temperatures. Both fulfill the requirements of the ISO 46 specification. While both fluids meet pump manufacturer requirements, the fluid with the higher viscosity index (VI) permits a broader Temperature Operating Window (TOW).
Note also the comparatively high viscosity of the High VI fluid when reaching high temperature (higher volumetric efficiency) as well as its comparatively lower viscosity at low temperatures (higher mechanical efficiency).
 

Maximize pump efficiency

While the amount of conveyed oil grows with increased viscosity, the mechanical efficiency of the pump is decreasing.The overall efficiency of a pump is the product of both curves. Only with a suitable viscosity for its hydraulic fluid will a pump work efficiently.
If a hydraulic fluid can be maintained within an efficient viscosity range throughout its entire operating temperature spectrum, the pump will operate more efficiently. For this reason, DYNAVIS® technology imposes a performance standard for hydraulic fluids that requires a high viscosity index as well as high shear stability.