in the field of helical bladed rotors , and their sealing assemblies an improved upstream seal for mixer rotors is provided . it includes a bushing - like visco sleeve subassembly , a sleeve shaped metallic liner positioned abutting the visco sleeve ; a sleeve - like , visco seal having first and second peripheries , an l - shaped packing seat retainer , all configured to provide a single annular shaped inner chamber in which a single , rope - like packing component serves to minimize hardening of the packing assembly by minimizing feed particulate material leaking into the upstream visco seal .