2.13. AIR PRESSURE CHECKPOINTS
Control or instrument panels containing the many different gages and
switches may be located at different places in the locomotive cab. Their
arrangement may vary with each dieselelectric locomotive, but they are
always in a conspicuous place. The instrument panel normally contains two
air gages, one to show the air pressure in the main reservoir and the other
to show the air pressure in the brake pipe and cylinder. The gages are
tested once every 3 months and whenever any irregularity is noted. An
accurate test gage or deadweight tester is used in making the test; any air
gage found incorrect is repaired before being used again.
2.14. COMMUTATOR CHECKPOINTS
The main generator is turned by a direct drive connection with the
diesel engine. The electric current that the generator produces is passed
from the commutator through brushes and into the locomotive electrical power
system. Figure 2.12 shows the alternator slip rings for a.c. power to roof
cooling fans and traction motor blowers, with brushes and brush holders in
place. Proper generator or alternator operation and electrical output
depend upon the commutator or slip rings being clean and free of defects,
the brush holders being correctly positioned, and the brushes being free of
excessive wear. The commutator or slip rings are inspected for cleanliness;
no oil, carbon deposits, or dirt should accumulate on either; and the
segments of the rings should not be nicked or cracked or show burned or
blackened spots. If the plates are defective, repairs should be made before
the locomotive is operated. The brush holders should be securely in place
and positioned 1/8 inch above the commutator or slip rings. The brushes
contained by the brush holders should ride evenly on the commutator or slip
rings; if they show excessive wear, they should be replaced. If dirt or
carbon is permitted to accumulate on the brush holders, a short circuit may
occur. If the brushes are worn excessively or are defective, an open
circuit may occur. The same preventive maintenance inspection should be
made of the auxiliary generator; one is shown in figure 2.13. In this
illustration, the inspection plate has been removed to reveal a brush holder
and brush.
2.15. ENGINE OVERSPEED TRIP MECHANISM
When the diesel engine's speed becomes excessive, an overspeed trip
mechanism located in the cab stops the engine by preventing further fuel
injection into the cylinders. The resetting procedure varies with different
locomotives. Some trip mechanisms are reset
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