ME12002
HYDRAULIC SYSTEM
Fine Metering
Figure 3-90 Fine Metering 1 18 19, 20 304 P
System path Consumer port Pressure path Spool (section bucket) Pilot pressure
When pilot control lever for bucket (excavating) is slightly operated, pilot pressure P shifts the bucket spool (304) partially to the right. Path (19) partially opens and center bypass (2) partially closes. The hydraulic fluid separates: one portion flows through opening (7) and path (1), and the other portion flows through parallel path (20), path (19), and port (18). See Figure 3-90 and Figure 3-91.
Figure 3-91 Negative Control Valve Components For a larger view of Figure 3-91, see Figure 3-88 on page 107.
Flow from path (1) through opening (7) slightly decreases and pressure PN in path (6) slightly decreases. See Figure 3-90 and Figure 3-91. Pressure PN decreases and front pump (27) discharge increases. When pilot control lever continues to shift, spool (304) also shifts and closes path (2), and center bypass. Path (6) pressure decreases to “zero” and front pump (27) discharge increases to “maximum.” See Figure 3-90, Figure 3-91 and Figure 3-92. When pilot control lever for bucket (excavating) is slightly operated, it adjusts pump discharge, and this adjustment precisely moves the actuator.
Figure 3-92 Negative Control System Function For a larger view of Figure 3-92, see Figure 3-87 on page 107.
For rear pump (28), the same negative control operating principle occurs using opening (7). See Figure 3-91 and Figure 3-92. Printed in U.S.A
109
909768/BP1207
