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Brookeld Engineering Laboratories, Inc. Page 29 Manual No. M00-151-I0614
APPENDIX E - e Brookeld Guardleg
The guard leg was originally designed to protect the spindle during use. The rst applications of the
Brookeld Viscometer included hand held operation while measuring uids in a 55-gallon drum. It is
clear that under those conditions the potential for damage to the spindle was great. Original construction
included a sleeve that protected the spindle from side impact. Early RV guard legs attached to the dial
housing and LV guard legs attached to the bottom of the pivot cup with a twist and lock mechanism.
The current guard leg is a band of metal in the shape of the letter U with a bracket at the top that attaches
to the pivot cup of a Brookeld Viscometer/Rheometer. Because it must attach to the pivot cup, the
guard leg cannot be used with a Cone/Plate instrument. A guard leg is supplied with all LV and RV
series instruments, but not with the HA or HB series. It’s shape (shown in Figure E-1) is designed
to accommodate the spindles of the appropriate spindle set; therefore, the RV guard leg is wider than
the LV due to the large diameter of the RV #1 and RV #2 spindles. The LV and RV guardlegs are not
interchangeable.
The calibration of the Brookeld Viscometer/Rheometer is determined using a 600 mL Low Form Grifn
Beaker. The calibration of LV and RV series instruments includes the guard leg. The beaker wall (for
HA/HB instruments) or the guard leg (for LV/RV instruments) dene what is called the “outer boundary”
of the measurement. The spindle factors for the LV, RV, and HA/HB spindles were developed with the
above boundary conditions. The spindle factors are used to convert the instrument torque (expressed
as the dial reading or %Torque value) into centipoise. Theoretically, if measurements are made with
different boundary conditions, e.g., without the guard leg or in a container other than 600 mL beaker,
then the spindle factors found on the Factor Finder cannot be used to accurately calculate an absolute
viscosity. Changing the boundary conditions does not change the viscosity of the uid, but it does
change how the instrument torque is converted to centipoise. Without changing the spindle factor to
suit the new boundary conditions, the calculation from instrument torque to viscosity will be incorrect.
Practically speaking, the guard leg has the greatest effect when used with the #1 & #2 spindles of the
LV and RV spindle sets (Note: RV/HA/HB #1 spindle is not included in standard spindle set). Any
other LV (#3 & #4) or RV (#3 - #7) spindle can be used in a 600 mL beaker with or without the guard
leg to produce correct results. The HA and HB series Viscometers/Rheometers are not supplied with
guard legs in order to reduce the potential problems when measuring high viscosity materials. HA/
HB spindles #3 through #7 are identical to those spindle numbers in the RV spindle set. The HA/HB
#1 & #2 have slightly different dimensions than the corresponding RV spindles. This dimensional
difference allows the factors between the RV and HA/HB #1 & #2 spindles to follow the same ratios
as the instrument torque even though the boundary conditions are different.
The recommended procedures of using a 600 mL beaker and the guard leg are difcult for some customers
to follow. The guard leg is one more item to clean. In some applications the 500 mL of test uid
required to immerse the spindles in a 600 mL beaker is not available. In practice, a smaller vessel may
be used and the guard leg is removed. The Brookeld Viscometer/Rheometer will produce an accurate
and repeatable torque reading under any measurement circumstance. However, the conversion of this
torque reading to centipoise will only be correct if the factor used was developed for those specic
conditions. Brookeld has outlined a method for recalibrating a Brookeld Viscometer/Rheometer
to any measurement circumstance in More Solutions to Sticky Problems. It is important to note that
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