Emerson 168 168H and 68 Series Three-Way Switching Valves User Manual

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Bulletin 71.7:168
September 2009
Types 168, 168H, and 68-2 Three-Way, Snap-
Acting Switching Valves
The Types 168 and 168H three-way, snap-acting
switching valves provide fast, positive switching of
pneumatic pressures in response to a predetermined
change in a pneumatic input signal. These switches
can be used to open and close pneumatically operated
control valves, to load or exhaust pneumatic systems,
or to operate a variety of pneumatic equipment.
Units are available for handling body pressures up
to 150 psig (10,3 bar) with diaphragm pressures
from 2 to 150 psi (0,14 to 10,3 bar). Maximum and
minimum diaphragm pressure changes between
switching points are shown in Table 1. The
diaphragm pressures at which switching occurs are
determined by the locations of the adjusting nuts.
Types 168 and 168H switching valves are also
available with a manual reset lever (see Figure 4).
The Type 68-2, shown in Figures 1 and 3, is a three-way,
snap-acting switching valve that forms the valve body
portion of the Types 168 and 168H switching valves. A
manual reset switch, see Figure 4, may be adapted to
the Types 168 and 168H switching valves to provide for
manual reset. An extension of the trip lever allows the
Type 68-2 to be used as a manual switching valve.
 —Trip lever
motion increases spring load on the seat until
the lever and spring mechanism passes dead
center; then valve spring force “snaps” the rocker
to its alternate position. Soft seat construction
and fast switching action minimize leakage and
throttling between seat rings.
 —High and low tripping
pressures can be adjusted throughout diaphragm
pressure range.
Figure 1. Type 168 Switching Valve and Type 68-2 Trip Lever
 —With one
connection (either B or C) plugged, unit can be
used as on/off switch.
 —No brass or
bronze in trim parts.
 —Unit may be set
to automatically reset after tripping, keeping
the pressure within the selected range. With both
adjusting nuts in place, the unit trips at the upper
(or lower) pressure limit and resets automatically
when the lower (or upper) limit is reached. With
one adjusting nut in place, the unit trips at the high
(or low) pressure limit and remains in that position
until it is reset. Reset may be achieved by
removing the stem protector and tripping the switch
or by tripping an optional reset lever (see Figure 4).