Mechanical testing of hydraulic fluids

AbstractThe antiwear properties of hydraulic fluids are important because hydraulic pump and motor wear is costly. While international hydraulic fluid performance standards continue to be developed, e. g., the ISO/TC28/SC4 committee's draft ISO DIS 11158 ‘Specifications for mineral oil hydraulic fluids’, the normal hydraulic fluid performance specifications represent minimum requirements. Performance specifications for nonmineral oil hydraulic fluids are also being developed.Typically, both the user and the fluid manufacturer possess insufficient objective information about the antiwear properties of special fluids, e. g., environmentally acceptable hydraulic fluids (EAHF) or fire‐resistant hydraulic fluids (FRHF) for use in hydraulic equipment such as axial‐piston pumps, vane pumps or radial‐piston motors. Manufacturer's specifications must therefore be determined. The required lubrication properties can be determined by either laboratory pump tests or a field trial, often at the customer's expense. The lubrication properties of a hydraulic fluid should ideally be determined under conditions that are equivalent to field practice.This paper will discuss the use of the vane pump test and the FZG gear test to gauge ‘recommended’ hydraulic fluid performance; many non‐mineral hydraulic fluids, such as environmentally acceptable hydraulic fluids, fire‐resistant fluids or synthetic hydraulic fluids, cannot be used in axial‐piston systems based only on results obtained with these tests, and additional testing is always required. Proposals are made for testing of such fluids on a variable‐load test rig. These tests are done with axial‐piston pumps, or other similar displacement systems, and are intended to determine the industrial suitability of non‐mineral hydraulic fluids.