shaft sleeve with cartridge mechanical seal

[someguy79]

I'm going through the guide specifications (reference specs not tied to a particular project) and finding some curious things. One is that we are requiring a shaft sleeve to be used on centrifugal pumps that also have cartridge mechanical seals.

My impression was that since a cartridge mechanical seal's only parts in relative motion and in contact (or close contact) are the seal faces, protection of the shaft with a sleeve should not be necessary.

What is the purpose, if any of using a shaft sleeve on an overhung centrifugal sewage pump where a cartridge seal is also used?

Thank you for any interest and responses.

 

[Artisi]

The use of the shaft sleeve is a means of excluding the pump shaft from contact with the pumped product.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)