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.
> View Circulation Path for Backflush Circulation
Recommended Pumps:
> Teikoku
> Chempump G Series
> Chempump NC Series
Canned motor pumps with isolated motors are recommended for pumping liquids with a high concentration of solids (above 10%). This design separates the liquid in the motor section from the solids present in the process stream. The motor cavity is filled with a clean liquid that is compatible with the process stream. An auxiliary impeller, located on the rotor assembly, circulates this liquid through a heat exchanger where it is cooled before it re-enters the motor.
A throttle bushing, lip seal, or mechanical seal is used to keep the process fluid separated from the liquid in the motor. To ensure that no solids enter the motor section of the pump, a clean liquid is introduced as makeup volume through the motor section and then travels through the throttle bushing, lip seal or mechanical seal into the process flow. The makeup flow rate will vary depending on what type of device is used to separate the motor from the pump. > View Circulation Path for Vertical Gas Purged > View Circulation Path for Isolated Motor Recommended Pumps: > Teikoku > Chempump G Series > Chempump NC Series
If low concentrations of solids are present (less than 2%) and their size is relatively small (0.003â€), hardened bearings running against a hardened journals provide excellent results in long term operation and service life. The hard bearings and journals allow the solids to pass through the pump without causing damage.
Typical bearing materials are silicon carbide, tungsten carbide or aluminum oxide. The journal area of the shaft or a shaft sleeve is usually constructed of stellite, tungsten carbide or silicon carbide. Due to the differences in the coefficients of expansion of the hardened bearings and journals, pumps featuring hardened materials should not be run dry for any length of time. > Technical Data: Fail-Safe Silicon Carbide Bearing System Recommended Pumps: > Teikoku > Chempump G Series > Chempump NC Series
When solids are present in small amounts (less than 2%) or are only present during process-upset conditions, canned motor pumps designed with external circulation can be modified to have filters installed on the recirculation line. Cartridge-type filters are usually installed in the circulation line to trap particles as small as 10 microns depending on the type of cartridge selected. It may be necessary to install a differential pressure gauge and switch across the filter to detect when the cartridge is becoming clogged. Isolation valves installed across the filter should be used so the cartridge can be changed without isolating the pump from the system.
Filtering the circulation flow ensures that only the fluid entering the motor section of the pump is filtered as opposed to filtering the entire system. 
> View Circulation Path for Standard External Circulation Recommended Pumps: > Teikoku > Chempump G Series > Chempump NC Series