The mechanical seal assembly of this invention is constructed in such a manner to substantially
, if not totally, eliminate compressive loads on the outer periphery of the softer seal ring which causes distortions and deflections of this seal ringand leads to failure of the seal assembly. This is accomplished by encircling the softer seal ring and its back-up ring with a cylindrical member, and by providing one or more passages in the seal ring and back-up ring subassembly to insure equalizationof fluid pressures on their inner and outer surfaces. The fit of the cylindrical member around the seal ring and its back-up ring is such to permit fluid to exist therebetween and the outer surface of the cylindrical member is exposed to the highpressure fluid. Also, the seal ring and back-up ring subassembly is constructed so that axial fluid pressure on the back-up ring is sufficient to insure sealing of the mating faces of the soft seal ring and the back-up ring, and to limit thetransmissions of deflections of the back-up ring to the softer seal ring. Axial fluid pressures on the opposite sides of the stationary seal ring are substantially balanced, which insures little, if any, deflections of the softer seal ring which couldbe caused by axial pressure differentials.