168, 168H, and 68 Series
3
2.2 Loosen locknut (key 9). Use a screwdriver to
move the trip lever (key 2C) so that the visible end
points away from the spring case (key 2A). It might be
necessary to back the adjusting nut (key 7) and lock-
nut away from the trip lever to do this.
2.3 Rotate the adjusting nut toward the trip lever
until the nut just moves the trip lever to the alternate
position.
3. To set the upper switching pressure:
3.1 Apply a pressure to the diaphragm case (key
1) equal to the upper switching pint.
3.2 Loosen the locknut on the upper range adjust-
ing nut. Use a screwdriver to move the trip lever (key
2C) so that its visible end points toward the spring
case (key 2A). It may be necessary to back the adjust-
ing nut and locknut away from the trip lever to do this.
3.3 Rotate the upper range adjusting nut toward
the trip lever until the nut just moves the trip lever to
its alternate position.
4. Tighten each locknut against its respective adjust-
ing nut.
5. Replace stem protector and machine screws (key
11).
168 and 168H Series Manual Reset
Operation
Without Manual Reset Switch
With one adjusting nut removed, the unit will switch
with high (or low) diaphragm pressure and will remain
in that position until the stem protector (key 10, figure
3) is removed and the trip lever (key 2C, figure 4) is
manually moved to its normal position. Remove the
range adjusting nut (and its locknut) located nearer the
spring case (key 2A, figure 3) if switching at low dia-
phragm pressure only is desired. Remove the other
adjusting nut and locknut if switching with high dia-
phragm pressure only is desired. The remaining ad-
justing nut can be adjusted by the appropriate steps
given in the adjustment section.
To reset the unit after it has switched, remove the ma-
chine screws and stem protector (keys 11 and 10, fig-
ure 3), and use a screwdriver to return the trip lever
(key 2C, figure 4) to its normal position.
With Manual Reset Switch
When a manual reset switch (see figure 3) is used on
a unit in the single-pressure trip mode (either high or
low pressure set point requiring only one adjusting
nut), the end of the reset lever (key 20) in contact with
the trip lever (see section DD, figure 3) should be on
the opposite side of the trip lever from the adjusting
nut.
If it is necessary to change the reset lever position,
remove the self tapping screws (key 23). Slide the le-
ver out of the stem protector slots, and position it on
the other side of the trip lever and reinsert. Reattach
the indicator tag with the self-tapping screws, making
sure the arrow on the tag points in the same direction
as that required to reset the switch.
Maintenance
WARNING
To avoid personal injury or property
damage from sudden pressure release
or uncontrolled process fluid, isolate
the switching valve from the process,
release process pressure, and vent any
loading pressure before starting disas-
sembly.
Because of the care Fisher takes in meeting all
manufacturing requirements (heat treating, dimension-
al tolerances, etc.), use only replacement parts
manufactured or furnished by Fisher.
Replacing 168 or 168H Series Diaphragm
Key numbers in this procedure are shown in figure 3.
1. For a 168 Series switching valve, unscrew the hex
nuts (key 13) and remove machine screws (key 12).
2. For a 168H Series switching valve, loosen and re-
move the machine screws (key 12).
3. Remove diaphragm case (key 1).
4. Remove diaphragm (key 4). Install the new dia-
phragm with the rubber side of the diaphragm facing
the pressure chamber; the fabric side of the dia-
phragm should face the actuator spring (key 8).
5. Replace diaphragm case, cap screws, and hex
nuts (where applicable).