Effect of Operation Time on Oil Viscosity and Pump Efficiency

摘要

The objective of this work is to determine the relevance of the after-shear viscosity of multigrade hydraulic fluids to volumetric efficiency. For that purpose, we have analyzed flow rate data as a function of time obtained in several hydraulic pumps using a variety of fluids. This group includes the Eaton-Vickers V20 and V104 vane pumps, and a Denison T6C mobile vane pump. We have contrasted the decrease of kinematic viscosity of the test oils to the stability of the flow rate. This analysis has enabled us to assess the relative role of the in-service viscosity, as seen by the pumps, and of the kinematic viscosity of the sheared oils on volumetric efficiency of the pumps. If a shear test that adequately represents the severity of the service is used, the fluid's after-shear kinematic viscosity can be used to estimate the volumetric efficiency of a pump. Alternatively, one can use the dynamic viscosity under high shear rate for that purpose. The analysis suggests that even though the kinematic viscosity decreases over time, the in-service viscosity seen by the pump only changes slightly with time. Consequently, if an oil provides adequate volumetric efficiency during the first hours of operation, it will continue doing the same even after extended operation.