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EATON
Heavy-Duty Series 2 Hydrostatic Pumps Parts and Repair E-PUPI-TS004-E October 2004
Hydraulic Fluid
Recommendations
The ability of Eaton hydrostatic components to provide the desired performance
and life expectancy depends largely on the fluid used. One of the most important
characteristics to consider when choosing a fluid to be used in a hydraulic system
is viscosity. Viscosity choice is always a compromise; the fluid must be thin
enough to flow easily but thick enough to seal and maintain a lubricating film
between bearing and sealing surfaces. Viscosity requirements are specified later in
this document.
Fluid temperature affects viscosity. In general, as the fluid warms it gets thinner
and viscosity decreases. The opposite is true when fluid cools.
When choosing a fluid, consider the start-up and operating temperatures of the
hydrostatic system . Generally, the fluid is thick when the hydraulic system is
started. With movement, the fluid warms to a point where the cooling system
begins to operate. From then on, the fluid is maintained at the temperature for
which the hydrostatic system was designed.
In actual applications this sequence varies; hydrostatic systems are used in many
environments from very cold to very hot. Cooling systems also vary from very elab-
orate to very simple, so ambient temperature may affect operating temperature
Introduction
Viscosity and
Temperature
Cleanliness of the fluid is extremely important. Eaton recommends that the fluid
used in its hydrostatic components be maintained at ISO Cleanliness Code 18/13
per SAE J1165. The code allows a maximum of 2500 particles per milliliter greater
than 5 µm and a maximum of 80 particles per milliliter greater than 15 µm. When
components with different cleanliness requirements are used in the same system,
the cleanest standard should be applied. A reputable filter supplier can supply filter
information.
Cleanliness
Maintaining correct fluid viscosity and cleanliness level is essential for all
hydrostatic systems. Field testing and monitoring are the only ways to get accurate
measurements of system cleanliness. Test and establish fluid maintenance
schedules designed to meet the viscosity and cleanliness requirements.
Fluid Maintenance
Premium grade petroleum based hydraulic fluids will provide the best
performance. These fluids typically contain additives that are beneficial. Eaton rec-
ommends fluids that contain anti-wear agents, rust inhibitors, anti-foaming agents,
and oxidation inhibitors. Premium grade petroleum-based hydraulic fluids carry an
ISO VGA rating.
SAE grade crankcase oils may be used, but it should be noted that these oils may
not contain all of the recommended additives. Using crankcase oils may increase
fluid maintenance requirements.
Hydraulic fluids that contain V.I. (viscosity index) improvers, sometimes called
multi-viscosity oils, may be used. These V.I.-improved fluids are known to
“shear-down” with use. Their actual viscosity drops below the rated value. Fluid
maintenance must be increased if V.I.-improved fluids are used. Automotive
automatic transmission fluids contain V.I. improvers.
Synthetic fluids may be used. A reputable fluid supplier can provide information on
synthetic fluids. Review applications that require the use of synthetic fluids with
your Eaton representative.
Fluid Selection
