Sometimes the threads on valve stems become worn or damaged, making the valves inoperable. When this occurs, the stems must be replaced. Before the stem can be replaced, however, all pressure must be removed. Then, with pressure removed, disconnect and remove the bonnet and upper valve assembly. The remainder of the procedure depends on the type of stem used (that is, rising or nonrising stem) and other design factors. Basically, the procedure may be summarized as follows:
1. Run the stem down by turning it in a clockwise direction.
2. Rotate the stem in a clockwise direction until the stem threads are completely out of the threaded portion of the upper bushing.
3. Pull the stem out of the stuffing box.
4. Remove the wedge or disc from the stem.
5. Replace the old stem with a new one.
6. Reassemble in reverse order with new packing and gasket (when applicable).