(b) Kinematic Method--The Ubbelohde tube is
filled with oil to a prescribed level, and the
proper oil temperature is attained by immersion
of the tube in an oi! bath. When this
temperature is reached, the oil in one side of the
tube is raised by suction to a specified height.
Suction is then removed, and the oil Is allowed
to flow back down through a narrow capillary.
Observing the upper level of the oil, the tester
clocks the time required for this level to pass
between two calibrated marks on the glass.
filled with oil to a prescribed level, and the
proper oil temperature is attained by immersion
of the tube in an oi! bath. When this
temperature is reached, the oil in one side of the
tube is raised by suction to a specified height.
Suction is then removed, and the oil Is allowed
to flow back down through a narrow capillary.
Observing the upper level of the oil, the tester
clocks the time required for this level to pass
between two calibrated marks on the glass.
(c) Redwood and Engler Methods--These
methods are similar in general procedure to the
Saybolt.
methods are similar in general procedure to the
Saybolt.
Reporting the Results: Saybolt viscosities are
reported as the number of elapsed seconds
indicated by the timer. For Saybolt Universal
viscosities, the units are Saybolt Seconds Uni-
versal (SSU), and for Saybolt Furol viscosities,
the units are Saybolt Seconds Furol (SSF). For
a given oil, the Saybolt Universal value will run
about 10 times as high as the Saybolt Furol
value at the same temperature.
reported as the number of elapsed seconds
indicated by the timer. For Saybolt Universal
viscosities, the units are Saybolt Seconds Uni-
versal (SSU), and for Saybolt Furol viscosities,
the units are Saybolt Seconds Furol (SSF). For
a given oil, the Saybolt Universal value will run
about 10 times as high as the Saybolt Furol
value at the same temperature.
For kinematic viscosity, the formula is: kine-
matic viscosity in centistokes (cSt) = Ct where C
is the calibration constant of the particular
viscosimeter and t is the observed time of flow.
The value computed by this formula is reported
in centistokes, units of kinematic viscosity.
matic viscosity in centistokes (cSt) = Ct where C
is the calibration constant of the particular
viscosimeter and t is the observed time of flow.
The value computed by this formula is reported
in centistokes, units of kinematic viscosity.
Redwood and Engler viscosities are also based
on the time of flow and are reported as "Red-
wood seconds" or"Engler degrees," as the case
may be. In all instances, the test temperature is
reported along with the corresponding viscosity.
on the time of flow and are reported as "Red-
wood seconds" or"Engler degrees," as the case
may be. In all instances, the test temperature is
reported along with the corresponding viscosity.
Significance of Results: Viscosity is often the
first consideration in the selection of a lubricat-
ing oil. For most effective lubrication, viscosity
must conform to the speed, load, and tempera-
ture conditions of the bearing or other lubricated
first consideration in the selection of a lubricat-
ing oil. For most effective lubrication, viscosity
must conform to the speed, load, and tempera-
ture conditions of the bearing or other lubricated
part. Higher speeds, lower pressures, or lower
temperatures require an oil of a lower viscosity
grade. An oil that is heavier than necessary
introduces excessive fluid friction and creates
unnecessary drag.
temperatures require an oil of a lower viscosity
grade. An oil that is heavier than necessary
introduces excessive fluid friction and creates
unnecessary drag.
Lower speeds, higher pressures, or higher tem-
peratures, on the other hand, require an oil of a
higher viscosity grade. An oil that is too light
lacks the film strength necessary to carry the
load and to give adequate protection to the
wearing surfaces. For these reasons, viscosity
tests play a major role in determining the lubri-
cating properties of an oil.
peratures, on the other hand, require an oil of a
higher viscosity grade. An oil that is too light
lacks the film strength necessary to carry the
load and to give adequate protection to the
wearing surfaces. For these reasons, viscosity
tests play a major role in determining the lubri-
cating properties of an oil.
In addition to the direct and more obvious con-
clusions to be drawn from the viscosity rating of
an oil, however, certain information of an indi-
rect sort is also available. Since, to begin with,
the viscosity of the lube oil cut is determined by
its distillation temperature, it is apparent that
viscosity and volatility are related properties. In
a general way, the lighter the oil, the greater its
volatility, the more susceptible it is to evapora-
tion. Under high-temperature operating
conditions, therefore, the volatility of an oil, as
indicated by its viscosity, should be taken into
consideration.
clusions to be drawn from the viscosity rating of
an oil, however, certain information of an indi-
rect sort is also available. Since, to begin with,
the viscosity of the lube oil cut is determined by
its distillation temperature, it is apparent that
viscosity and volatility are related properties. In
a general way, the lighter the oil, the greater its
volatility, the more susceptible it is to evapora-
tion. Under high-temperature operating
conditions, therefore, the volatility of an oil, as
indicated by its viscosity, should be taken into
consideration.
Though the significance of viscosity test results
has been considered from the standpoint of new
oils, these tests also have a place in the
evaluation of used oils. Oils drained from crank-
cases, circulating systems, or gear boxes are
often analyzed to determine their fitness for
further service or to diagnose defects in ma-
chine performance.
has been considered from the standpoint of new
oils, these tests also have a place in the
evaluation of used oils. Oils drained from crank-
cases, circulating systems, or gear boxes are
often analyzed to determine their fitness for
further service or to diagnose defects in ma-
chine performance.
An increase in viscosity during service may
often indicate oxidation of the oil. Oxidation of
the oil molecule Increases its size, thereby thick-
ening the oil. When oxidation has progressed to
the point of causing a material rise in viscosity,
appreciable deterioration has taken place.
often indicate oxidation of the oil. Oxidation of
the oil molecule Increases its size, thereby thick-
ening the oil. When oxidation has progressed to
the point of causing a material rise in viscosity,
appreciable deterioration has taken place.
A-19 (FIST 2-4 11/90)