Cartridge type mechanical seal description

First, what is "Cartridge type" Mechanical seal? What is advantage?

Cartridge type all components device are integrated in a sealed water seal box, the moving ring is positioned by "Positioning pin" and shaft sleeve。After the sealing device installed on the pump, it can be used by removing the positioning pin, there is no need to adjust the compression dynamic and static ring, so the pressure is the most reasonable, the average service life is more than 3 years, relative to the "Bulk" mechanical seal, the cartridge mechanical seal has accuracy and life advantages.