Figure 3-1.—Saybolt viscometer.used to express the fluid’s viscosity, in Sayboltuniversal seconds or Saybolt furol seconds.The glass capillary viscometers, shown infigure 3-2, are examples of the second type ofviscometer used. These viscometers are used tomeasure kinematic viscosity. Like the Sayboltviscometer, the glass capillary measures the timein seconds required for the tested fluid to flowthrough the capillary. This time is multiplied bythe temperature constant of the viscometer in useto provide the viscosity, expressed in centistrokes.The following formulas may be used toconvert centistrokes (cSt units) to approximateSaybolt universal seconds (SUS units).For SUS values between 32 and 100:For SUS values greater than 100:Although the viscometers discussed above areused in laboratories, there are other viscometersin the supply system that are available for localuse. These viscometers can be used to test theviscosity of hydraulic fluids either prior to theirbeing added to a system or periodically after theyhave been in an operating system for a while.Figure 3-2.–Various styles of glass capillary viscometers.3-2
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