PISTON 1998188 - Caterpillar

Illustration 1 g03494777
Pressure circuit for SWING RIGHT (partial schematic)
(1) Passage (supply oil)
(2) Makeup port
(3) Relief valve
(4) Passage
(5) Motor rotary group
(6) Swing motor
(7) Passage (return oil)
(8) Relief valve
(9) Passage
(10) Makeup line
(11) Check valve
(12) Port (supply oil)
(13) Port (return oil)
(14) Check valve
(15) Check valve
(17) Swing control valve
(18) Return check valve
(19) Return line When the swing joystick is moved to the NEUTRAL position during the swing right operation, the swing control valve shifts to the NEUTRAL position. Since the swing control valve is in the NEUTRAL position, the oil delivery through port (12) to motor rotary group (5) is blocked at the swing control valve. The return oil from the motor rotary group through port (13) 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. This action causes an internal leak of oil in the swing motor. As a result, a vacuum condition occurs at passage (1). In order to prevent this vacuum condition, makeup oil is delivered from the return hydraulic system to the swing motor.
Illustration 2 g03494776
(10) Makeup line
(18) Return check valve
Illustration 3 g03494778
(15) Check valve
(18) Return check valve When all of the control valves for implements, swing and travel are in the NEUTRAL position, the oil delivery from the front pump and the rear pump flows through return line (19) to the hydraulic tank. Return check valve (18) is attached to the hydraulic control valve. Return check valve (18) maintains the return oil pressure at 300 kPa (43.5 psi) in return line (19). If a vacuum condition occurs at the swing motor during the stop of a swing operation, the return check valve (18) causes return oil to flow to motor rotary group (5) as makeup oil. The 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 (7) and port (13) to return line (19). The return oil pressure in passage (7) increases but the return oil pressure in passage (7) remains lower than the pressure setting of swing relief valve (8). Swing relief valve (8) remains in the CLOSED position.A vacuum condition occurs at port (12) and passage (1) due to the insufficient oil delivery from the rear pump and due to the tendency of the motor rotary group to continue to rotate. Since relief valve (8) remains in the CLOSED position, makeup oil does not flow through relief valve (8), passage (9) and check valve (11) to passage (1) to motor rotary group (5).Makeup oil is supplied to motor rotary group (5) from return line (19). Return oil flows from return line (19), through makeup line (10), and through port (2). Return oil then flows through passage (9), through check valve (11), through