HEAD 4J0538 - Caterpillar

Swing Priority
The pilot oil pressure from the pilot control valve directly corresponds to the amount of movement or position of the joystick. The pilot oil pressure from the pilot control valve acts on the pressure reducing valve for swing priority and the variable swing priority valve. As the swing joystick is moved farther from the NEUTRAL position, the pilot oil pressure increases. This gradual increase in pilot oil pressure causes a gradual change to swing priority. Thus, swing priority is controlled by the position of the swing joystick and swing priority automatically activates when the joystick reaches a certain position.When swing priority is activated, the output flow from the left pump supplies hydraulic oil to the swing hydraulic circuit. Since swing priority increases the swing acceleration, swing priority is useful for loading operations. Swing priority is also useful for leveling operations and trenching operations when higher swing force is required.
Illustration 4 g00812571
Stick I control valve (swing priority OFF) (15) Parallel feeder passage (20) Variable swing priority valve (22) Passage (24) Pilot line (swing pilot pressure) (27) Pressure reducing valve for swing priority (38) Pilot line (pilot system pressure) (39) Pin hole (40) Spool (41) Spring (42) Passage (stick I) (43) Spool (44) Drain line (45) Check valve (46) Orifice (47) Line (48) Passage (50) Spring (51) Passage (56) Drain Line
Illustration 5 g00821462
SWING RIGHT operation (swing priority OFF) (4) Swing motor (13) Parallel feeder passage (15) Parallel feeder passage (18) Swing control valve (19) Stick I control valve (20) Variable swing priority valve (21) Passage (22) Passage (23) Pilot control valve (swing and stick) (24) Pilot line (26) Pilot line (27) Pressure reducing valve for swing priority (28) Left pump (29) Right pump (30) Pilot pump (38) Pilot line (41) Spring (47) Line (48) Passage (50) SpringWhen the swing joystick is in the NEUTRAL position, no pilot oil pressure acts on spool (40) of pressure reducing valve for swing priority (27). Full pilot oil pressure flows through pilot line (38), the pressure reducing valve for swing priority (27), line (47) and passage (22) to variable swing priority valve (20). Spool (43) in the variable swing priority valve is shifted upward against the force of spring (41). The oil delivery from left pump (28) in parallel feeder passage (13) flows through parallel feeder passage (15) and variable swing priority valve (20). The oil delivery enters stick I control valve (19) .When the swing joystick is moved slightly from the NEUTRAL position in order to perform a SWING RIGHT operation, reduced pilot oil pressure from pilot control valve (23) flows through pilot line (26). The pilot oil then divides into two flow paths. Part of the pilot oil flows through passage (21) to swing control valve (18). The spool in the swing control valve shifts a slight amount that corresponds to the amount of movement of the swing joystick. The remainder of the pilot oil flows through pilot line (24) and passage (48). The pilot oil pressure acts on the shoulder of spool