Page 129 - Valve Selection Handbook

116 Valve Selection Handbook

3. U-shaped rubber liner that is bonded to a metal band. This combina-
tion can be inserted into a split valve body, as in the valve shown in
Figure 3-72.

To ensure that rubber-lined butterfly valves achieve their full sealing
capacity, they must be correctly installed. Two requirements must be
observed:

1. The rubber liner should be fully supported by the pipe flanges. The
pipe flanges should therefore be of the weld-neck type rather than
the slip-on type. In the case of slip-on flanges, the rubber liner
remains unsupported between the valve bore and the outside diame-
ter of the pipe. This lack of support of the liner tends to promote dis-
tortion of the liner during valve operation, resulting in early wear
and seat leakage.
2. When installing the valve, the disc must initially be put into the
near-closed position so as to protect the rim of the disc from damage
during handling. Prior to tightening the flange bolts, the disc must
be rotated into the fully open position to permit the liner to find its
undisturbed position.

Figure 3-72. Butterfly Valve with Resilient Replaceable Liner and
Interference-Seated Disc, Liner Bonded to Steel Band, Valve Body Split in
Two Halves. (Courtesy of DeZurik.)