This specific double-ported globe valve happens to be stem-guided, with bushings guiding the higher stem and in addition a lower stem (on the bottom facet of the valve body). In a single-ported globe valve, there'll solely be one drive generated by the method pressure.
This pushes the cage down on the lip of the seat and holds it firmly to the physique of the valve. Seat may also be threaded and screwed right into a thread reduce in the same space of the physique. However this method makes elimination of the seat ring during maintenance tough if not unimaginable. Seat rings are additionally typically beveled at the seating surface to allow for some guiding in the course of the final phases of closing the valve.
In a double-ported globe valve, there might be two opposed pressure vectors, one generated on the upper plug and one other generated at the lower plug. Thus, the seat ring acts as a guide for the plug to maintain the center-strains of the plug and seat all the time aligned, minimizing guiding stresses that would in any other case be positioned on the stem. Yet one other variation on the globe valve design is the port-guided valve, where the plug has an uncommon shape, projecting into the seat. The seat ring supplies a stable, uniform and replaceable shut off floor.