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Introduction
The ability of Eaton hydrostatic components to provide
the desired performance and life expectancy depends
largely on the fluid used. The purpose of this document
is to provide readers with the knowledge required to
select the appropriate fluids for use in systems that
employ Eaton hydrostatic components.
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 for Eaton’s
Heavy Duty Hydrostatic product line are specified later in
this document.
Viscosity and Temperature
Fluid temperature affects viscosity. In general, as the
fluid warms it gets thinner and its viscosity decreases.
The opposite is true when fluid cools. When choosing a
fluid, it is important to 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 se-
quence varies; hydrostatic systems are used in many
environments from very cold to very hot. Cooling sys-
tems also vary from very elaborate to very simple, so
ambient temperature may affect operating temperature.
Equipment manufacturers who use Eaton hydrostatic
components in their products should anticipate tempera-
ture in their designs and make the appropriate fluid
recommendations to their customers.
Cleanliness
Cleanliness of the fluid in a hydrostatic system is ex-
tremely important. Eaton recommends that the fluid used
in its hydrostatic components be maintained at ISO
Cleanliness Code 18/13 per SAE J1165. This code allows
a maximum of 2500 particles per milliliter greater than 5
µ
m and a maximum of 80 particles per milliliter greater
than 15
µ
m. When components with different cleanliness
requirements are used in the same system, the cleanest
standard should be applied. OEM’s and distributors who
use Eaton hydrostatic components in their products
should provide for these requirements in their designs. A
reputable filter supplier can supply filter information.
Fluid Maintenance
Maintaining correct fluid viscosity and cleanliness level is
essential for all hydrostatic systems. Since Eaton hydro-
static components are used in a wide variety of applica-
tions it is impossible for Eaton to publish a fluid mainte-
nance schedule that would cover every situation. Field
testing and monitoring are the only ways to get accurate
measurements of system cleanliness. OEM’s and dis-
tributors who use Eaton hydrostatic components should
test and establish fluid maintenance schedules for their
products. These maintenance schedules should be
designed to meet the viscosity and cleanliness require-
ments laid out in this document.
Fluid Selection
Premium grade petroleum based hydraulic fluids will
provide the best performance in Eaton hydrostatic
components. These fluids typically contain additives that
are beneficial to hydrostatic systems. Eaton recommends
fluids that contain anti-wear agents, rust inhibitors, anti-
foaming agents, and oxidation inhibitors. Premium grade
petroleum based hydraulic fluids carry an ISO VG rating.
SAE grade crankcase oils may be used in systems that
employ Eaton hydrostatic components, but it should be
noted that these oils may not contain all of the recom-
mended additives. This means using crankcase oils may
increase fluid maintenance requirements.
Hydraulic fluids that contain V.I. (viscosity index) improv-
ers, sometimes called multi-viscosity oils, may be used in
systems that employ Eaton hydrostatic components.
These V.I. improved fluids are known to “shear-down”
with use. This means that 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 in Eaton hydrostatic compo-
nents. A reputable fluid supplier can provide information
on synthetic fluids. Review applications that require the
use of synthetic fluids with your Eaton representative.
Hydraulic Fluid Recommendations