tween 1/32"-1/16", and may be adjusted by
shimming or bending the stop (see Fig. 1) for the
latch. This is a high speed mechanism and these
adjustments should be maintained if satisfactory
operation is to be expected.
In connection with the spring pressure on the
latch, it might be pointed out that the roller on the
main lever passes the nose of the latch very fast,
which means that the latch spring must have
sufficient compression to snap the latch into place
quickly before the air supply is shut off or the main
lever bounces open. The 3/16" overtravel dimen
sion is an important factor here since it allows the
latch time to snap into place. However, too much
spring compression will make the breaker harder
to latch and reduce the number of operations
possible before re-charging the storage tank.
It has already been pointed out that the breaker
reclosing time is primarily determined by setting of
the "b" contact (see diagram Fig. 3) which is a
special contact on the 2-pole auxiliary switch. The
pressure setting of the pneumatic governor also
affects the breaker reclosing time, and should be
adjusted to settings given on nameplate. The ad
justing screw at the right on top of the governor
switch controls the cut-off point, while the screw at
CAS-8 OPERATING MECHANISM
the left controls the differential. Another factor
affecting the reclosing time is the amount of com
pression on the breaker accelerating spring.
The automatic throttle in the air intake will not
affect the breaker reclosing time if adjusted properly.
The adjusting screw in the top of the slot of the
throttle operating link should be adjusted so that the
throttle toggle will not be snapped over center to
limit the air intake until the breaker is very nearly
to the full open position. Thus on a fast reclosing
operation, the throttle will remain wide open since
the breaker does not go all the way open. The ad
justing nuts on the lower end of the throttle stem
below the intake casting (see Fig. 2) determine the
size of air passage for the limiting position (breaker
open) of the throttle. Turning these nuts clockwise
pulls the piston down to form a larger air passage.
Adjusting these nuts will require an adjustment on
the screw on the top of the slotted link.
It is best to make these adjustments when the
breaker is open in order to make sure that the pin
on the main lever is not jammed in the top of the
slot. Do not change throttle adjustments unless there
is some good reason for doing so. Opening the
throttle wider for faster closing operation will abuse
the breaker unnecessarily.
MAINTENANCE
Caution:
When working around the mecha
nism or breaker, close the hand valve between
the compressor and mechanism and open the
control circuit at the control panel so that
accidental operation of the magnet valve
or
contactor will not cause the breaker to close
unexpectedly.
It is desirable to inspect the mechanism and com
pressor at regular intervals and be sure of its con
dition by making several operations, particularly at
first if not familiar with pneumatic mechanisms. It
is necessary to keep moving parts, particularly the
latch and switches, clean and free from foreign
matter or rust. Note that the space heater which is
energized continuously (winter and summer) will
minimize rusting. It is also desirable to make one or
more close-open operations of the breaker in order
to make the exhaust valve operate. Otherwise the
breaker may be in service a number of years before
closing on a fault and causing the exhaust valve to
operate.
The automatic latch and trigger are made of
high-grade steel machined to shape, with the latch
ing surfaces ground smooth after hardening. The
engaging surfaces of the latch and trigger may be
polished with fine emery cloth if they become dirty.
Apply a thin film of rust inhibitor to the latch and
trigger where the latch hooks over the roller, and
where the trigger engages the latch. This inhibitor
should be carefully selected to be free-flowing at
all anticipated temperatures, non-hardening, and
self-healing (does not completely wipe off in one
operation). A light graphite lubricant is suggested,
or other material with similar properties. The
latching surfaces should be examined at every in
spection to make sure that they are not gummed up.
Important:
Do not attempt to grind the
latching surfaces or change their angle.
If the low pressure switch available for operating
a low pressure alarm in the station is used, there
should be no danger that air pressure will not be
11
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