Figure 3-1.Saybolt viscometer.
used to express the fluids viscosity, in Saybolt
universal seconds or Saybolt furol seconds.
The glass capillary viscometers, shown in
figure 3-2, are examples of the second type of
viscometer used. These viscometers are used to
measure kinematic viscosity. Like the Saybolt
viscometer, the glass capillary measures the time
in seconds required for the tested fluid to flow
through the capillary. This time is multiplied by
the temperature constant of the viscometer in use
to provide the viscosity, expressed in centistrokes.
The following formulas may be used to
convert centistrokes (cSt units) to approximate
Saybolt universal seconds (SUS units).
For SUS values between 32 and 100:
For SUS values greater than 100:
Although the viscometers discussed above are
used in laboratories, there are other viscometers
in the supply system that are available for local
use. These viscometers can be used to test the
viscosity of hydraulic fluids either prior to their
being added to a system or periodically after they
have been in an operating system for a while.
Figure 3-2.Various styles of glass capillary viscometers.