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Non-Rising Stem Valve Design
In the last few illustrations we saw valves where the stem rises out of the valve structure as the valve is opened. Under certain condition you may have limited head room above the valve.
Under such conditions, we use a design, which we refer to as "non-rising" stem valve assembly.
The figure shown here illustrates a non-rising stem valve.
In this design the position of the stem is fixed in the valve structure. The stem is allowed to rotate, but held in place with a collar. The stem is connected to the disc through a threaded screw type configuration. In this design threads on the lower end of the stem screw into or out of the disc as the stem is turned. As the stem is rotated, the disc is forced to move up and down the threaded part of the stem.