The solids will prevent the inner seal from moving forward as the faces wear and if the barrier fluid pressure is lost, solids will penetrate the inner seal faces. Be sure to vent vertical pumps back to the suction side of the pump. Air trapped in the stuffing box can cause the seal faces to run hot and in some instances destroy the elastomer. Plated faces can have the hard coating crack off and filled carbons can have the binder melted out in high heat. The corrosion rate of all liquids increases with temperature.
Thermal expansion can cause seal face loads to alter and seal face flatness to change.
Many products will change from a liquid to a solid or gas in the presence of high temperature. If this should occur between the seal faces, they can be blown open. Do not be tempted to put the mechanical seal outside of the stuffing box to keep the springs out of the fluid. In these applications centrifugal force is throwing solids into the lapped faces and if there is excessive pressure in the system the seal faces will be blown open. When choosing the pressure range of a mechanical seal be sure to consider the stuffing box pressure not the pump discharge pressure.