Scraper Operations

CONTROL LEVERS Most scrapers have three basic control levers located on the right side of the operator’s 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