Cartridge unit A ready-to-install seal cartridge, in which all parts of the mechanical seal form a compact unit together with the shaft sleeve, casing parts, connection flange and torque transmission element. Individual parts of the seal can be fitted and removed in advance in the workshop, making for faster and more reliable and installation removal of the seal at the machine by even less well-trained staff. Use of cartridge units reduces plant down-time periods and enables mechanical seals to be installed in hard-to-reach places.