554 Forwarder and 574 Forwarder Hydraulic System Caterpillar

The swing system uses two cylinders to rotate the boom. The cylinders move a rack. The rack rotates a pinion gear that is attached to the boom. The swing system is composed of the left implement hydraulics joystick, the IQAN, the implement control valve, a crossover relief valve, and the swing cylinders.

Illustration 1	g00508864
Schematic of the Swing System (1) Swing cylinder (2) Pinion gear (3) Left implement hydraulics joystick (4) Swing cylinder (5) Crossover relief valve (6) IQAN (7) Implement control valve

When the operator moves joystick (3), voltage flows from the control lever to IQAN (6). The IQAN then sends current to the corresponding proportional solenoids in implement control valve (7). As the joystick is moved further from the NEUTRAL position the current increases. As the current increases, the speed of the function increases.

The magnitude of the current to the proportional solenoids controls the movement of the solenoids. The movement of the solenoids controls the oil flow to swing cylinders (1) and (4). When oil flows to the swing cylinders, the cylinders rotate pinion (2). The pinion causes the boom to rotate.

If an external force acts on the boom, the stick, or the grapple, the pressure in the swing circuit will increase. When the pressure exceeds the pressure setting of the relief valves in crossover relief valve (5), the relief valves open. Pressure oil flows through the relief valve to the return circuit of the swing system.