HARNESS AS 2917928 - Caterpillar

BOOM RAISE Operation
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Boom lowering control valve (1) Spring (2) Valve (4) Passage (5) Port (9) Line relief valve (10) Port (11) Passage (12) Load check valveWhen the operator moves the joystick to the BOOM RAISE position, pump oil flows through port (5) through check valve (12) to passage (11). This allows pump oil to flow through passage (11) and port (10) to the head end of the boom cylinders (9). The rod is extended and the boom raises.When the joystick is returned to the NEUTRAL position, spring (1) shifts valve (2) and passage (4) is blocked. Valve (2) and load check valve (12) prevent the cylinder rod from retracting.BOOM LOWER Operation
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(1) Spring (2) Valve (3) Rod (4) Passage (5) Port (6) Piston (7) Passage (8) Port (9) Line relief valve (10) Port (11) Passage (12) Load check valve (13) PassageWhen the operator moves the joystick to the BOOM LOWER position, pilot oil flows from port (8) to passage (13) and passage (7). The pilot pressure forces piston (6) and rod (3) against valve (2). Valve (2) shifts against the force of spring (1). Passage (4) is opened. This allows return oil to flow through port (9), passage (10), passage (4), and port (5) to the return line. The cylinder rod retracts, and the boom lowers.When the joystick is returned to the NEUTRAL position, spring (1) shifts valve (2) and passage (4) is blocked. Valve (2) and load check valve (12) prevent the cylinder rod from retracting.Manual Boom Lower
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(1) Port (15) Port (21) Seat (22) Locknut (23) Valve (24) BallAs seat (21) is turned counterclockwise, ball (24) will shift. As ball (24) is shifted, oil is allowed to flow through port (1) and valve (23) to port (15). Oil from the head end of the boom cylinder flows through port (15) to the hydraulic tank. This allows the boom to lower.