An improved mechanical seal assembly is provided for hydro transport applications and other similar applications, such as large high pressure slurry pumps. This mechanical seal is used in large scale pumps having an axially adjustable shaft to accommodate high wear applications by maintaining suitable pump performance. The improved seal is a cartridge seal that includes a stationary seal adapter which is mounted to a pump casing and has a static gasket sealingly contacting a movable gland which non-rotatably supports the stationary seal rings of a mechanical seal. Additional seal rings are rotatably supported on the shaft wherein these rotatable and non-rotatable seal components are movable axially with the shaft to improve pump performance in high-wear conditions. The gland and non-rotatable seal rings are supported on and move with a bearing housing, along with the shaft and its seal rings.