A general misconception about canned motor pumps is that they can only be used on clean, cool fluids because of their tight internal clearances and the fact that the bearings must be lubricated by the pumped fluid. In truth, canned motor pumps are ideal for leakproof pumping of solids-laden fluids - even slurries - if they are properly designed. Some configurations for pumping solids or slurries are:
Backflushing is recommended when the solids content of the process fluid is above 2 percent.
First, a clean fluid that is compatible with the process is introduced into the motor section of the pump. The backflush fluid lubricates the bearings, cools the motor, then becomes part of the process stream. Instrumentation including a flow meter, pressure gauge, and control and/or check valves should be installed on the backflush line to assure that the proper flow rate is maintained through the pump. The backflush flow rate will vary depending on the size of the pump and the application load.
To prevent solids from entering the motor section of the pump, the backflush fluid should be started at least 30 seconds prior to energizing the pump and should continue to operate at least 30 seconds after the pump is shut down.