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| Illustration 1 | g06018674 |
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Pressure circuit for SWING RIGHT operation (partial schematic) (1) Check valve (2) Makeup port (3) Relief valve (4) Passage (5) Passage (6) Makeup line (7) Port (8) Check valve (9) Slow return check valve (10) Return line (11) Return line (12) Swing control valve (13) Port (14) Passage (15) Relief valve (16) Passage (17) Relief valve (18) Motor rotary group (19) Swing motor | |
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| Illustration 2 | g06018668 |
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Swing motor compartment (2) Makeup port (3) Relief valve (6) Makeup line (15) Relief valve (19) Swing motor | |
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| Illustration 3 | g03376464 |
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Swing relief valve (Typical example) (4) Passage (20) Orifice (21) Spring (22) Stem (23) Piston chamber (24) Passage (25) Piston (26) Passage (27) Piston chamber (28) Orifice (29) Passage (30) Plug | |
Relief valves (3) and (15) are located in the head of swing motor (19). These relief valves limit the pressure in the left and right swing circuits to the swing relief valve setting. The relief valves provide a cushion effect at a start or stop of the swing operation.
The flow of return oil from through port (1) inside motor rotary group (18) is blocked at swing control valve (12). The oil flow is blocked due to swing control valve (12) being in the NEUTRAL position. The pressure of the blocked oil in passage (5) increases because the machine still rotates due to the weight of the upper structure. The increased oil pressure in passage (5) acts upon swing relief valve (3). The increased pressure oil forces stem (22) of relief valve (3) to the right (open position) against the force of spring (21). When stem (22) shifts, oil flows through passage (4), check valve (17) and into motor rotary group (18). The shock load is absorbed at the stop of a swing movement.
At swing relief valve (3), the increased oil pressure in passage (5) flows through orifice (20). The oil then flows into passage (26) and into piston chamber (27). The force of spring (21) is less than the relief valve pressure setting. This causes stem (22) to move to the right (open position) before the oil pressure in passage (5) reaches the relief valve pressure setting. At the same time, the pressure oil in piston chamber (27) flows through passages (24) and (29). Piston (25) moves to the left against the force of spring (21). The oil in piston chamber (23) flows through orifice (28) and into piston chamber (27). Orifice (28) restricts the oil flow into piston chamber (27).
The swing relief valve maintains the operating pressure of the swing hydraulic circuit at a lower pressure than the swing relief valve setting until the pressure in the swing hydraulic circuit forces piston (25) to the right against plug (30). When piston (25) contacts plug (30), the pressure in piston chamber (27) increases. The oil pressure in passage (5) reaches the swing relief valve setting. The oil in passage (5) flows around stem (22) and into passage (4).
After stem (22) begins to open and before piston (25) completes the movement to the left, the pressure in the swing hydraulic circuit increases gradually. The pressure in the swing hydraulic circuit does not reach a peak pressure. This function is called a two-stage relief operation. The two-stage relief operation absorbs the shock load at the stop of a swing operation.