A seal that runs three years on clean water can fail in three months on pulp black liquor. The seal did not change. The face pair did. Reaction-bonded silicon carbide handles dirty, fibrous media. Carbon graphite is the default for clean duty but grooves fast in black liquor. Tungsten carbide takes heavy slurry but runs brittle and costly. Pairing the faces to the medium can move seal life by an order of magnitude. The FBU EDMH and ESMH ship preset for pulp and paper black liquor.