opened no more than two turns or 20 percent of its
Outside screw and yoke (OS&Y) valve position
indicators (figs. 8-24 and 8-25) are firmly attached to
the valve yoke (fig. 8-26). The spring-loaded switch-
operating lever or plunger rests in a smoothly
tapered notch in the valve stem. When the valve is
operated, the stem moves in or out; the lever or
plunger moves up the incline at the edge of the
notch. The switch is actuated before the lever or
plunger is out of the notch. This causes a
supervisory signal at the control unit and/or remote
A post indicator valve (PIV) will have a posi-
tion indicator mounted to it (fig. 8-27). Usually
Figure 8-24.OS&Y valve position switch (plunger type).
Figure 8-25.OS&Y valve position switch (lever type).
a PIV is located outside the building and may be
mounted on the ground or on the building wall. A
spring-loaded lever rests against the side of the
open/shut indicator, called a target. As the valve is
operated, the target moves. The switch follows this
movement. The position indicating switch is
adjusted to cause a supervisory signal before the
operating nut has rotated two turns or 20 percent of
its full travel.
Nonrising stem valve position indicators are
attached to nonrising stem valves, usually installed
underground. The housing of the device is made of a
noncorroding material such as brass. The switch
itself is a magnetically operated, sealed reed switch.
As the valve is operated, the magnet moves away
from the reed switch. After the valve has
Figure 8-26.OS&Y valve position supervisory switch