Dual diameter valve stem packing

A packing arrangement for a valve stem which extends through a packing chamber formed in the valve stem bore of a valve housing having a flow passage therethrough and a valve element secured to the valve stem and mounted within said housing for opening or closing the flow passage, said packing chamber being provided with packing stops at its opposite ends and characterized by a stepped dual diameter configuration formed by successive enlargements of the valve stem bore, with one enlargement of the bore providing a first packing chamber section located nearest the flow passage and the other enlargement providing a second packing chamber section of larger diameter and cross-sectional area than said first packing chamber section which is adjacent thereto, one of said packing stops being an inner packing stop exposed to the fluid pressure of the flow passage and the other packing stop being an outer packing retainer ring located at the other end outwardly of the inner packing stop with respect to the flow passage and being axially adjustable with respect to said bore, said packing arrangement further including:

• a primary packing assembly positioned within the first packing chamber section between the valve stem and the chamber wall is surrounding relation to said valve stem and in engagement with said inner packing stop and fabricated of layers of elastomeric or polymeric materials suitable for providing primary sealing under normal temperature operating conditions;
• a rigid packing support ring loosely received about the valve stem and positioned within the second packing chamber section outwardly of said low temperature packing assembly and in engagement therewith;
• a secondary packing assembly positioned within the second packing chamber section between the valve stem and the wall of the packing chamber in surrounding relation to the valve stem and located outwardly of said support ring so as to be sandwiched between said outer packing stop and said support ring and fabricated of materials suitable to provide sealing under abnormally high temperatures, said outer packing retainer ring being axially adjusted to a position whereby said primary packing assembly is energized in sealing contact with the valve stem and chamber wall at normal temperature conditions below the decomposition temperature of the primary packing materials, and said secondary packing assembly is energized in sealing contact with the valve stem and chamber wall to provide a sealing relationship therewith at abnormally high temperature conditions which impair the stem sealing relationship of the primary packing assembly so that the packing structure will not leak flow passage fluid when subjected to abnormally high temperatures and pressures.