Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Slurry Pumps 243
ing the pump speed by changing the sheave ratios. Three to five percent
should be added to the motor BMP to compensate for belt losses. It is
always good practice to add one more belt than is normally calculated to
cover upset conditions and belt breakage.
Motors must be rated with an adequate margin to cover upset conditions
such as high flow due to lower-than-expected system losses, higher
concentrations, and start-up. At start-up, the concentration is often
higher, and if the pump was not flushed out during the previous shutdown,
the pump could be plugged with solids requiring high breakaway
torques to get the impeller rotating. This undesirable condition happens
all too frequently and can cause pump damage, excessive wear, and motor
overload.
Under well-controlled systems, free from upset, the motor could be
rated at 20% above the motor shaft BMP; however, this percentage could
Figure 13-10. Typical belt-driven, overhead-motor-mounted slurry pump.