Dual seal designs for dangerous and expensive products or any time back up protection is needed. Inside mounted designs that take advantage of centrifugal force to throw solids away from the lapped seal faces. Cartridge seals to ease installation and allow you to make impeller adjustments without disturbing the seal face loading. Split seal designs that allow you to install and change seals without taking the pump apart and disturbing the alignment. Hydrodynamic or non-contacting seals used for the sealing of gases.
Hydrostatic designs are another version of non-contacting vapor seals.
Almost all-original equipment designs do. There are many seal designs available that will not cause fretting corrosion or damage shafts and sleeves, and that is the kind you should be using. The seal should have built in non-clogging features such as springs out of the fluid. The seal should be able to compensate for a reasonable amount of both radial and axial movement of the shaft. The seal should be designed to be positioned as close to the bearings as possible to lessen the affects of shaft deflection.