Effect of VI Improver on the In-Service Viscosity of Hydraulic Fluids

A vane pump rig of the type used in ASTM D-2882 was used to study the permanent and temporary shear loss characteristics of hydraulic fluids containing a variety of VI improvers. The influence of polymethacrylate VI improver molecular weight on performance was studied. Severity of hydraulic oil service was assessed relative to that tor automotive engine oils, and the suitability of common VI improvers is discussed. It was shown that shear stable polymethacrylate VI improvers can provide a high level of performance for extended periods of time.