TM 5-2410-240-23-1
0011
IMPLEMENT HYDRAULIC SYSTEM CONTINUED
2. Blade Raise
The blade raise circuit will have the highest signal oil pressure in the hydraulic system when it is the only hydraulic
circuit in operation. When the operator moves the joystick to the RAISE position, pilot oil enters the control valve
through the port (Figure 8, Item 21) and pilot oil from the proportional solenoid valve flows into the passages
(Figure 8, Items 18 and 14). The spool (Figure 8, Item 10) moves to the left when the pilot oil overcomes the force
of the spring (Figure 8, Item 12). Pump supply oil flows from the passage (Figure 8, Item 17) around the spool to
the feeder passage (Figure 8, Item 19) and then to the pressure compensator valve (Figure 8, Item 7), where it
flows into internal passages. As the pressure compensator valve moves upward, a cross-drilled passage opens to
an internal passage in the valve. In turn, some of the hydraulic oil flows around the pressure compensator valve to
the signal pressure passage (Figure 8, Item 6).
N OT E
Hydraulic oil that flows to the signal pressure passage (Figure 8, Item 6) and the internal
passage is signal oil. The signal oil balances the pressure compensator valve (Figure 8,
Item 7) against the hydraulic oil pressure in the feeder passage (Figure 8, Item 19). This
controls the flow across the spool (Figure 8, Item 10).
The signal oil, in the signal pressure passage (Figure 8, Item 6), flows to the pressure compensator valve in each
control valve. The signal oil also flows to the pump control valve on the implement pump. The signal oil helps to
control the output of the implement pump. The implement pump upstrokes and the hydraulic oil pressure in
passage (Figure 8, Item 17) and feeder passage (Figure 8, Item 19) increases. When pressure in the feeder
passage rises above circuit pressure, it unseats the check valves (Figure 8, Items 5 and 8) and oil flows to the
bridge passages (Figure 8, Items 16 and 20). In the bridge passages, the spool (Figure 8, Item 10) blocks the flow
of oil. However, in the bridge passages, hydraulic oil flows around the spool, into the passage (Figure 8, Item 15),
and then through the port (Figure 8, Item 9), where it flows to the rod end of the blade raise cylinders. From there,
oil returns to the valve through the port (Figure 8, Item 4) and flows into the passage (Figure 8, Item 3), around the
spool, into the passage (Figure 8, Item 2), and then into the tank.
When the operator releases the joystick, the flow of pilot oil to the valve is blocked and the pilot oil in the passage
(Figure 8, Item 14) drains to the tank. The loss of pilot oil enables the spring (Figure 8, Item 12) to move the spool
(Figure 8, Item 10) to the HOLD position. Check valves (Figure 8, Items 5 and 8) close and the spool and check
valves block the hydraulic oil in the hydraulic lines.
The blade raise circuit has a relief valve (Figure 8, Item 11) and a makeup valve (Figure 8, Item 1). The relief valve
(Figure 8, Item 11) makes sure that the pressure in the RAISE cylinders does not exceed a preset limit. The relief
valve also acts as a dead engine LOWER valve. Turning the dead engine LOWER screw (Figure 8, Item 13) opens
the passage between the cylinders and the tank. The makeup valve makes sure that the cylinders do not cavitate
when the blade is raising and lowering.
0011-12
