Abstract: A seal system for a motor pump unit includes a primary and a plurality of backup seals mounted in series within a seal housing. The primary seal is of a hydrostatic type and each of the backup seals is of a normally closed hydrodynamic type. Each of the primary and backup seals has a secondary seal between an axially movable seal ring thereof and the fixed seal housing, and at least one of these secondary seals is a spring-loaded, split piston ring seal. Two of the backup seals are of the Rayleigh type, where the Rayleigh pockets are formed in the seal runner, and the sealing dam is formed on the axially movable seal ring. An insert is provided in the runner of one of the backup seals, which insert is formed from a relatively harder material than the material forming the sealing dam. The other Rayleigh-type backup seal has pumping grooves extending downwardly and inwardly through the runner and toward the shaft to pump liquid into the Rayleigh pockets to ensure proper seal operation.