CONTROL LEVERS
Most scrapers have three basic control levers
located on the right side of the operators seat. The first
lever is the bowl lever (fig. 10-38, view A). The bowl
lever raises and lowers the bowl. The middle lever is
the apron control lever (fig. 10-38, view B). The apron
control lever opens and closes the apron, allowing the
required amount of material to enter or be ejected from
Figure 10-38.-Scraper control levers.
the bowl. The third lever is the ejector lever (fig. 10-39,
view C). The ejector lever forces the dirt out of the bowl.
For maximum hydraulic cylinder operating efficiency,
the engine should be operated at maximum rated speed
and the control levers moved to their extreme operating
position.
SCRAPER OPERATIONS
The greatest engine power is available when the
engine is running at top governed speed. The proper
transmission gear ratios must also be engaged to obtain
maximum engine power output. When the transmission
is placed in a too high a gear ratio for full engine power,
the result is a stall condition in the transmission
converter. Stalling the converter prevents the engine
from operating at maximum efficiency and results in
rapid overheating and premature wear of the converter
or transmission.
The transmission must be downshifted correctly
while the scraper is in motion to prevent damage to the
power train. Improper downshifting overspeeds the
transmission and engine and usually results in
premature wear and unnecessary transmission
breakdowns.
When moving the scraper from a full stop, always
start with the transmission in low gear, depressing the
throttle for the degree of acceleration required. A wide,
open throttle provides the fastest acceleration under
full-load conditions.
When running downgrade, avoid overspeeding the
engine by keeping the scraper speed at, or below, the
maximum speed for the transmission range engaged. As
a general rule, downhill scraper speed should not exceed
5 mph more than that attained on level ground in the
transmission ratio engaged.
When the selected transmission ratio is too high,
slow the scraper with the service brakes until the
transmission can be properly downshifted to the
required range for the grade.
Downhill speed can be slowed, if necessary, by
lowering the scraper bowl until the cutting edge drags
enough to slow the scraper to the required speed to
permit proper downshifting or stopping.
Do not fan the brakes by repeated depressing and
releasing. This practice can reduce air pressure below
the point required for proper breaking. The air pressure
system should indicate 105 to 125 psi on the air pressure
gauge for effective braking. When the gauge indicates
a pressure drop below 105 psi for a long time, shutdown
the scraper until the trouble is corrected.
10-20