Abstract: A centrifugal pump assembly comprises a pump housing defining a pump cavity, a drive shaft rotatably mounted to the housing, an impeller rotatably disposed in the housing and operatively coupled to the drive shaft, and a shaft seal disposed between the shaft and the housing. At least one sensor is operatively connected to the housing for detecting whether a slurry in the housing has migrated radially inwardly a predetermined extent. Pressurizing componentry is operatively connected to the housing for injecting pressurized air into the housing at a point between the shaft seal and a rotating slurry ring in the housing upon detection by the sensor that a slurry-air interface has moved radially inwardly beyond the location of the sensor. The sensor and the pressurizing componentry thus generate and maintain a gaseous buffer zone between the slurry and the shaft seal during operation of the pump assembly.