The materials for DYGRF mechanical seals are mainly silicon carbide/sic as the rotary seal faces and silicon carbide/sic as the mating rings with some kinds of o-rings, retainers and metal sleeves/bushings/bushes need to be welded together and spring seats and bushes too, so mechanical seals should be tested by a core rod or a plug to see if the inside diameter of mechanical seals are OK.
