George, there is no such thing as a clean service. There is only dirty and less dirty. There will always be little surprises that don't quite make it into the data sheet.
Every centrifugal pump(sealed, mag-drive, canned motor) has to address 3 issues in solids applications; Clotting the impeller, abrasion, and clogging the lubricating flowpath.
For clogging the impeller, this generally dictates maximum particle size and could force impeller design changes from closed to (semi)open.
Abrasion will impact materials selected and sizing as less abrasion will happen with lower speeds and minimized internal recirculation.
Bearing frames aside, all pumps require some type of lubrication. Seals need fluid to pass across seal faces. It can be a liquid or a gas and the flow can possibly go either way but that lubrication is still needed. The standard off the shelf centrifugal pump is not put into any sort of slurry service. The manufacturer would use some combination of flow modifiers and/or external flushes to keep that lubricating flowpath clean. Sealless pumps can offer similar features and the product group has come a long way since they first were introduced but the solids loading limits of sealless pumps still lags sealed pump technology.
