The stem and disc of butterfly valve are separate parts. The disc is drilled to receive the rod. Two methods are used to secure the disc to the valve stem so that the disc rotates when the valve stem rotates. In the first method, the disc is drilled and fixed to the valve stem with bolts or pins. Another method is to drill the disc as before, and then shape the upper stem hole to fit the square or hexagonal stem. This method allows the disk to “float” and find its center in the seat. Uniform sealing is achieved and external stem fasteners are eliminated. This assembly method is advantageous in covering disks and corrosive applications.
In order to hold the disc in place, the stem must extend beyond the bottom of the disc and fit into the bushing at the bottom of the valve body. One or two similar bushings also follow the upper part of the stem. These bushings must be resistant to the medium being treated or sealed so that corrosive media cannot come into contact with them.
Stem sealing can be achieved by packing or O-ring seal in traditional stuffing box. Some valve manufacturers, especially those specialized in handling corrosive materials, place stem seals inside the valve so that the material handled by the valve will not come into contact with the stem. If a stuffing box or external O-ring is used, the fluid passing through the valve will come into contact with the stem.
Post time: Oct-15-2021