Model 35 Viscometer Instruction Manual
208878 Revision N, February 2013 18
5.4 Changing the Rotors, Bobs, and Torsion Springs
The R1-B1-F1 rotor-bob-torsion spring combination is standard for all Fann
viscometers. Other rotor-bob combinations may be used, provided shear rates are
calculated for the fluid being tested. Rotor-bob combinations other than R1-B1
have large gap sizes; as a result, the shear stress dial readings are not consistent
with readings from a smaller gap.
The following instructions explain how to remove and replace the rotors, bobs, and
torsion springs.
Calibration is required when torsion springs are changed.
Changing the rotors and bobs only reconfigures the geometry of
the shear gap. These changes do not affect the torsion springs,
bearings, or shaft. Therefore, calibration is not required when
changing rotors or bobs.
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