HYDRAULIC SYSTEM •
If both travel spools (301R) and (301L) operate simultaneously or if only travel right spool (301R) operates, hydraulic fluid flows into path (15) (not shown), then through path (16) (not shown), shuttle valve (11) (not shown), and into pilot path (12). See Figure 3-101 and Figure 3-104 on page 115.
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If only travel left spool (301L) operates, hydraulic fluid flows into path (9), then through path (5), path (6), shuttle valve (11) (not shown), and into pilot path (12). See Figure 3-101, Figure 3-102, and Figure 3-104 on page 115.
If path (13) pressure is less than main relief valve (601) set pressure, valve washer (24) and seat (25) are shut-off and hydraulic fluid in path (13) cannot flow into return path (14). See Figure 3-101 and Figure 3-103 on page 115. While traveling, path (12) pilot pressure flows through path (25) and into the left end of piston (17). Piston (17) moves to the right and presses against spring (39), increasing the spring force pressure. When path (13) hydraulic fluid is pressurized close to the high pressure setting, valve washer (24) opens against spring (39). Hydraulic fluid in chamber (33) then flows through path (32) and into return path (14), with its pressure decreased. See Figure 3-101 and Figure 3-103 on page 115. Hydraulic fluid pressure in path (13) moves piston (37) to the left and presses against the right end of plug (40). Simultaneously, path (13) hydraulic fluid flows into path (30), with its pressure decreased by opening (31). Hydraulic fluid pressure in spring chamber (35) decreases because fluid flows through path (36) and into path (30). The pressure from path (13) presses plunger (38) to the left against spring (34). Plunger (38) opens and path (13) hydraulic fluid flows into return path (14), maintaining the high pressure setting. Adjustment plug (26) adjusts the high pressure setting. See Figure 3-101 on page 115.
909768/BP1207
ME12002 Operating Main Relief
Figure 3-105 Main Relief Operation While Working While traveling, the force pressing against spring (39) decreases, and the force pressing against valve washer (24) decreases. See Figure 3-105. When path (13) is pressurized close to the working pressure setting, valve washer (24) opens. Plunger (38) opens and path (13) hydraulic fluid flows into return path (14) to maintain the working pressure setting. Adjustment screw (25) adjusts the working pressure setting. See Figure 3-105.
Port Relief Valve
Figure 3-106 Port Relief Valve Port relief and make-up valves are installed between the cylinders and spools of working components (boom, dipper arm, and bucket). When an external force acts on a cylinder rod, and its spool is in neutral, pressure within the cylinder can become excessive. Port relief valve restricts this pressure to the valve set pressure.
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Printed in U.S.A
