Suction recirculation will bring fluid into the stuffing box from behind the impeller, where it is usually cleaner. This works on most closed impeller pump applications and those open impeller pump applications where the impeller adjusts to the volute rather than the back plate. Flush with a clean liquid from an outside source. A pressurized barrier fluid between two seals can keep solids from penetrating between the faces if the faces should open. Build the seal to compensate for operating extremes.
Slurry features that can be part of seal design.
The elastomer moves to a clean surface as the face wears. Keep the sealing fluid on the outside diameter of the seal to take advantage of centrifugal force that will throw solids away from the lapped faces. Rotate the fluid with the seal to prevent erosion of the seal components. A simple vane arrangement can accomplish this. Use two hard faces if you find it impossible to keep the lapped seal faces together.