The boom drift reduction valve is placed in the boom circuit between the main control valve and the boom cylinders. When the joystick for the boom is in the NEUTRAL position, the boom drift reduction valve stops oil leakage from the head end of the boom cylinders. Stopping oil leakage prevents boom drift.
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| Illustration 1 | g06616696 |
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Main control valve (1) Boom drift reduction valve | |
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| Illustration 2 | g06356446 |
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Boom drift reduction valve (3) Passage to head end of boom cylinders (6) Passage (7) valve (8) Spool (11) Passage (12) Spring (15) Boom cylinder (16) Boom 1 control valve (17) Boom 2 control valve | |
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| Illustration 3 | g06356452 |
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Boom drift reduction valve (BOOM RAISE) (1) Boom drift reduction valve (2) Passage from boom 2 control valve (3) Passage to head end of boom cylinders (4) Passage from boom cylinder retract solenoid (5) Passage (6) Passage (7) valve (8) Spool (9) Drain passage (10) Spring chamber (11) Passage (12) Spring (13) Passage from boom 1 control valve (14) Spring (15) Boom cylinder (16) Boom 1 control valve (17) Boom 2 control valve | |
When raising the boom, pilot oil is not sent from the pilot manifold to passage (4) of the boom drift reduction valve. Spool (8) does not shift.
The oil flow from the boom 2 control valve in passage (2) and boom 1 control valve in passage (13) combines in the main control valve at the boom drift reduction valve passage (6). As the oil pressure in passage (6) increases, valve (7) shifts against the force of spring (12). The oil in spring chamber (10) flows through passages (5) and (11) to passage (6). The oil flow in passage (6) now flows to the head end of the boom cylinders through passage (3).
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| Illustration 4 | g06356561 |
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Boom drift reduction valve (BOOM LOWER) (1) Boom drift reduction valve (2) Passage from boom 2 control valve (3) Passage to head end of boom cylinders (4) Passage from boom cylinder retract solenoid (5) Passage (6) Passage (7) valve (8) Spool (9) Drain passage (10) Spring chamber (11) Passage (12) Spring (13) Passage from boom 1 control valve (14) Spring (15) Boom cylinder (16) Boom 1 control valve (17) Boom 2 control valve | |
When lowering the boom, pilot oil is sent from the pilot manifold to passage (4) of boom drift reduction valve (1). Spool (8) shifts against spring (14). The oil in spring chamber (10) flows through passage (5) and spool (8). The oil then flows through drain passage (9) to the hydraulic tank.
The return oil from the boom cylinder head end enters passage (3). Since the pressure in spring chamber (10) is low, the oil in passage (3) shifts valve (7) against the force of spring (12). The oil from the head end of the boom cylinders flows through passage (6) to the boom control valves.