Page 94 - Valve Selection Handbook

Manual Valves 81

• An electrical drive for wedge gate valves is more complicated than for
parallel gate valves in that the drive must be torque-limited instead of
travel-limited. The operating torque of the drive must thereby be high
enough to effect the wedging of the wedge into the seats while the
valve is being closed against the full differential line pressure. If the
valve is closed against zero differential pressure, the wedging of the
wedge into the seats becomes accordingly higher. To permit the valve to
be opened again against the full differential pressure, and to allow also
for a possible increase of the operating effort due to thermal movements
of the valve parts, the operator must be generously sized.

The limitations of wedge gate valves are otherwise similar to those of
parallel gate valves.
Efforts to improve the performance of wedge gate valves led to the
development of a variety of wedge designs; the most common ones are
described in the following section.

Figure 3-36. Wedge Gate Valve with Plain Solid
Wedge, Union Bonnet, and Internal Screw.
(Courtesy of Crane Co.)

Figure 3-37. Wedge Gate Valve with Clamped
Bonnet, Internal Screw. (Courtesy of Crane Co.)