The boom drift reduction valve is placed in the boom circuit between the boom 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 | g06016418 |
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Boom drift reduction valve BOOM RAISE (1) Port (2) Passage (3) Valve (4) Spool (5) Boom drift reduction valve (6) Passage (7) Passage (8) Spring | |
When the joystick is moved to the BOOM RAISE position, the oil from the control valve (boom I) and the control valve (boom II) flows through port (2) and into boom drift reduction valve (5). The oil acts on the face of valve (3). Because no oil is sent to passage (6) from the pilot control valve, spool (4) remains stationary. Passage (7) is blocked by spool (4).
Oil flow from boom II control valve and boom I control valve combine. The combined oil flows into port (2). Oil pressure at port (2) overcomes the force of spring (8). Valve (3) moves upward. Spring (8) is compressed. Oil from port (2) flows through port (1). Oil from port (1) flows into the head end of the boom cylinders.
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| Illustration 2 | g06016431 |
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Boom drift reduction valve BOOM LOWER (1) Port (2) Port (3) Valve (4) Spool (5) Boom drift reduction valve (6) Passage (7) Passage (8) Spring (9) Passage (10) Port (11) Passage (12) Spring chamber (13) Passage (14) Passage (15) Port | |
When the joystick is moved to the BOOM LOWER position, pilot oil from the pilot control valve flows through port (15) and into boom drift reduction valve (5). The pilot oil flows through passage (6) to spool (4). The oil then shifts spool (4) to the left. The oil in spring chamber (12) flows through passage (7), and passage (9). The oil then flows out of port (10) through drain line to the hydraulic tank. The oil pressure in spring chamber (12) now decreases.
Return oil from the head end of the boom cylinders enters boom drift reduction valve (5) through port (1). Because the oil pressure in spring chamber (12) is low, valve (3) begins to open by moving up. The return oil now flows through valve (3) and into passage (13). In passage (13), the oil flow divides into two flow paths. Part of the oil flows through passage (11), spool (4) and passage (14) to the rod end of the boom cylinders. The remainder of the oil flows from passage (13) through port (2) into the control valve (boom I) and back to the hydraulic tank.