TECHNOLOGY
FEATURE
in which phosphate ester fluids are used are
manufactured from specific materials.
c) Polyol ester based synthetic
hydraulic fluids
Polyol esters are produced by the reaction
of long-chain fatty acids and synthesized
alcohols. Polyol ester based hydraulic fluids
are fire resistant and possess very good lubrication properties. They are environmentally
friendly but their use is limited by high cost.
d) Water glycol synthetic
hydraulic fluids
Water glycol based fluids contain 35-60% of
water in form of solution (not emulsion) and
additives (anti-foam, anti-freeze, rust and corrosion inhibitors, anti-wear etc.).
Water glycol based hydraulic fluids possess
excellent fire resistance, they are non-toxic
and biodegradable. However, their temperature range is relatively low: 32°F - 120°F (0°C
- 49°C). Water evaporation causes deterioration of the hydraulic fluids properties.
e) Vegetable hydraulic oils
Vegetable hydraulic oils are produced mainly
from Canola oil. Their chemical structure is
similar to that of polyol esters.
Vegetable hydraulic oils possess very good
lubrication properties and high viscosity
index (low temperature sensitivity of viscosity).
They are non-toxic and biodegradable. The
main disadvantage of vegetable hydraulic oils
is their relatively low oxidation resistance.
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A CAT truck busy at a road construction site. Most of its functions rely on hydraulics.
Viscosity of hydraulic oils
ISO Designation of hydraulic oils
Viscosity of a hydraulic fluid depends on
its composition and the temperature. Low
viscosity limit is determined by the lubrication properties of the oil and its resistance to
cavitation. Upper viscosity value is limited by
the ability of the oil to be pumped.
Common viscosity of hydraulic oils is in the
range of 16 - 100 centistokes. Optimum viscosity value is 16 - 36 centistokes.
International Standardization Organization (ISO) established a viscosity grading
(VG) system for industrial hydraulic oils.
According to the system, hydraulic oils are
designated by the letters ISO followed by a
number equal to the oil viscosity measured in
centistokes at 40°C (104°F). Examples include:
ISO VG 32, ISO VG 46, ISO VG 68, ISO VG 100,
ISO VG 150 etc.
.
Lubezine Magazine | January-March 2012