312F and 313F Excavator Machine Systems Oil Makeup (Swing System) Caterpillar

Illustration 1	g06018703
Pressure circuit for SWING STOP (partial schematic) (1) Check valve (2) Makeup port (3) Relief valve (4) Passage (5) Passage (6) Makeup line (7) Port (8) Slow return check valve (9) Valve housing (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 (21) Hydraulic oil cooler (22) Hydraulic tank (23) Bypass check valve

When the swing joystick is moved to the NEUTRAL position during the swing right operation, the swing control valve shifts to the NEUTRAL position. The oil delivery through port (13) to motor rotary group (18) is blocked at the swing control valve. The return oil from the motor rotary group through port (7) is also blocked at the swing control valve. The upper structure will attempt to continue to rotate after the swing joystick is returned to the NEUTRAL position. When the upper structure attempts to continue to rotate, an internal leak of oil in the swing motor is caused. As a result, a vacuum condition occurs at passage (16). In order to prevent this vacuum condition, makeup oil is delivered from the return hydraulic system to the swing motor.

Illustration 2	g06018714
(6) Makeup line (9) Valve housing (20) Main control valve (21) Hydraulic oil cooler (22) Hydraulic tank

Illustration 3	g06018717
Swing motor compartment (2) Makeup port (6) Makeup line (19) Swing motor

Illustration 4	g06018723
(8) Slow return check valve (9) Valve housing (21) Hydraulic oil cooler (23) Bypass check valve

When all the control valves for implements, swing, and travel are in the NEUTRAL position, oil delivery from the idler pump flows through main control valve (20) . The oil then flows into return line (11) and back into the hydraulic tank. Valve housing (9) is located between return line (11) and the hydraulic tank. Slow return check valve (8) maintains the return oil pressure at 290 kPa (42 psi) in return line (11). If a vacuum condition occurs at the swing motor during the stop of a swing operation, the slow return check valve causes oil from return line (11) to flow into motor rotary group (18) as makeup oil. The slow return check valve eliminates the vacuum condition in the swing motor due to internal leakage.

If the swing joystick is moved suddenly toward the NEUTRAL position from the FULL STROKE position, the swing control valve partially closes. Until the swing control valve reaches the NEUTRAL position, the return oil from the swing motor continues to flow through passage (5) and port (7). The return oil pressure in passage (5) increases but the return oil pressure in passage (5) remains lower than the pressure setting of swing relief valve (3). Swing relief valve (3) remains in the CLOSED position.

A vacuum condition occurs at port (13) and passage (16) due to the insufficient oil delivery from the idler pump. A vacuum condition occurs due to the tendency of the motor rotary group to continue to rotate. Since relief valve (3) remains in the CLOSED position, oil does not flow through relief valve (3), passage (4), and check valve (17) to motor rotary group (18).

Return oil flows from return line (11) through makeup line (6). Makeup oil is supplied to motor rotary group (18) by flowing through port (2), check valve (17), and into motor rotary group (18). The vacuum condition in passage (16) is eliminated by the makeup oil from the return hydraulic system.

During a left swing operation, the return ports and the supply ports of the swing motor are reversed. Makeup oil flows through check valve (1) if a vacuum condition occurs in passage (5) during a swing left operation.