switch or located in a remote space and
The types of mechanically operated switches are
connected to the switch by a capillary tube. The
the push-action (type A-S) and the cam-action (types
temperature range at which the switches
P and P41). The push-operated switch, provided for
operate is adjustable at X (fig. 2-15).
bulkhead mounting, is a single-throw or multiple-
throw, momentary action, normally open push
switch. The push-action mechanism uses a straight-
Temperature-operated switches are used with
line movement of the shaft to operate the electrical
the circulating-water, high-temperature alarm
contacts. The cam-action switch consists of two SPDT
system; cruising-turbine exhaust alarm system;
sensitive switches operated by two adjustable cams
and generator-air, high-temperature alarm
mounted on the rotor shaft (fig. 2- 17).
The cam-action mechanism uses a rotary motion of
the shaft to move cams, which in turn operate
sensitive switches. The points of operation of the
Mechanically operated switches are used in
sensitive switches are varied by adjusting the
many types of installations, such as wrong-
angular positions of the cams with respect to the
direction alarms and valve-position indicators.
shaft on which they are mounted. Mechanical
switches are used with the following systems:
Widely used because of their small size and
excellent dependability, they are commonly
called "micro switches, " or properly called
sensitive switches. ("MICRO SWITCH" is a
These switches will open or close a circuit
Submersible steering-gear alarm
with a very small movement of the tripping
device. They are usually of the push-button
DW Wrong-direction alarm
variety, and depend on one or more springs for
their snap action. For example, the heat of the
sensitive switch is a beryllium copper spring,
heat-treated for long life and unfailing action.
contributes to the long life and dependability of
this switch. The basic sensitive switch is shown
in figure 2-16.
A water switch consists of a pair of terminals
mounted in an insulated base within a cast
fitting (fig. 2-18). T h e r e i s a 7 0 0 0 - o h m , 5 - w a t t
resistor connected across the two terminals,
which limits the current to the required
value for the supervisory circuit when the
Figure 2-16.--Sensitive switch.
Figure 2-17.--Cam-action mechanical switch.