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.