TYPES OF VALVES
Solid Wedge Gate Valve
The solid wedge gate valve shown in Figure 5 is the most
commonly used disk because of its simplicity and strength.
A valve with this type of wedge may be installed in any
position and it is suitable for almost all fluids. It is practical
for turbulent flow.
The flexible wedge gate valve illustrated in Figure 6 is a
one-piece disk with a cut around the perimeter to improve
the ability to match error or change in the angle between the
seats. The cut varies in size, shape, and depth. A shallow,
narrow cut gives little flexibility but retains strength. A
deeper and wider cut, or cast-in recess, leaves little material
at the center, which allows more flexibility but compromises
A correct profile of the disk half in the
Flexible Wedge Gate Valve
flexible wedge design can give uniform
deflection properties at the disk edge,
so that the wedging force applied in
seating will force the disk seating
surface uniformly and tightly against the seat.
Gate valves used in steam systems have flexible wedges. The
reason for using a flexible gate is to prevent binding of the gate
within the valve when the valve is in the closed position. When
steam lines are heated, they expand and cause some distortion of
valve bodies. If a solid gate fits snugly between the seat of a valve
in a cold steam system, when the system is heated and pipes
elongate, the seats will compress against the gate and clamp the
valve shut. This problem is overcome by using a flexible gate,
whose design allows the gate to flex as the valve seat compresses it.
The major problem associated with flexible gates is that water tends
to collect in the body neck. Under certain conditions, the admission
of steam may cause the valve body neck to rupture, the bonnet to lift
off, or the seat ring to collapse.
Following correct warming
procedures prevent these problems.