Page 80 - Know and Understand Centrifugal Pumps
P. 80
Pump Classification
w Considered more reliable than canned motor pumps (the contain-
ment shell is larger).
The disadvantages
w Higher initial cost and repair cost.
w Not good at handling abrasives.
w Must be operated very close to the REP on the curve.
Cannot run dry.
rn Cannot resist extended cavitation.
The magnets can decouple (requiring stopping and restarting the
Pump ).
w Not as efficient as conventional pumps.
w May require larger motors.
w Tends to heat the pumped liquid.
Canned motor pumps
~~-..
These pumps incorporate an electric motor whose rotary assembly is
hermetically sealed inside a stainless steel or exotic alloy can. The
motor, pump shaft and bearings all operate wet inside the pumped
liquid as shown in Figure 6-12.
The advantages
w Requires no mechanical seal.
w Only two bearings.
w No product loss.
w Considered leak proof.
w No product exposure to workers or the environment (although
some owners manuals offer instructions on what to do ‘in case of
breach-of-containment’ .
The disadvantages
w Higher initial cost and repair cost.
w Fine abrasives will damage the bearings.
w Must be operated very close to the BEP on the curve.
w Cannot run dry or under cavitation.
