Page 109 - Valve Selection Handbook

96 Valve Selection Handbook

gap between the seatings is therefore relatively wide, so the valve
achieves a satisfactory seat seal only with liquids that have a high surface
tension or viscosity. However, if the plug has been coated with a grease
prior to installation, the valve may be used also for wet gases such as wet
and oily compressed air.
The lubricated taper plug valve shown in Figure 3-55 is similar to the
lubricated cylindrical plug valve except for the shape of the plug. Both
valves may also serve the same duties. However, the lubricated taper
plug valve has one operational advantage. Should the plug become
immovable after a prolonged static period or as a result of neglected
lubrication, the injection of additional sealing compound can lift the plug
off the seat just enough to allow the plug to be moved again. When free-
ing the plug in this way, the gland should not be slackened as is some-
times done by users, but should rather be judiciously tightened. On the
debit side, it is also possible to manually overtighten the plug and cause
the plug to seize in this way.
The valve shown in Figure 3-56 is a lubricated taper plug valve in
which the plug is mounted in the inverted position and divorced from the
stem. The plug is adjusted in its position by a screw in the valve cover

Figure 3-56. Lubricated Taper Figure 3-57. Taper Plug Valve with PTFE Body
Plug Valve with Inverted Sleeve. (Courtesy ofXomox Corporation,
Pressure-Balanced Plug. "Tuttine.")
(Courtesy of Nordstrom.)