Owner manual

Brookfield Engineering Laboratories, Inc. Page 72 Manual No. M/98-211-A0701
The Brookfield Guardleg
The guard leg was originally designed to protect the spindle during use. The first applications of the
Brookfield Viscometer included hand held operation while measuring fluids 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 Brookfield
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 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 spindle. They are not
interchangeable.
The calibration of the Brookfield Viscometer/
Rheometer is determined using a 600 ml Low
Form Griffin 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) define 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 fluid, 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. 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 difficult for some
customers to follow. The guard leg is one more item to clean. In some applications the 500 ml of test
fluid 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 Brookfield Viscometer/Rheometer will produce an
RV Guardleg
LV Guardleg