Butterfly Valve Disk and Stem Assemblies:

The stem and disk for a butterfly valve are divided pieces. The disk is bored to receive the stem. There are two methods are used to secure the disk to the stem so in which the disk rotates as the stem is turned. Within the first method, the disk is bored by and secured to the stem within pins or bolts. The instead method includes boring the disk as before, after that shaping the upper stem bore to fit a squared or hex-shaped stem. This technique permits the disk to "float" and find its center within the seat. Uniform sealing is completed and external stem fasteners are eliminated. That method of assembly is advantageous within the case of covered disks and inside corrosive applications.

In sequence for the disk to be held within the proper position, a stem must extend beyond the bottom of the disk or fit within a bushing in the bottom of the valve body. A single or two same bushings are along the upper portion of the stem as well. Those bushings must be either resistant to the media being handled or sealed so in which the corrosive media cannot come within contact along with them.

Stem seals are accomplished either along with packing within a conventional stuffing box or through means of O-ring seals. A few valve manufacturers, particularly those specializing within the handling of corrosive materials and place a stem seal on the inside of the valve so which no material being handled through the valve could come within contact along with the valve stem. The fluid passing through the valve will come into contact with the valve stem if a stuffing box or external O-ring is employed.