PUMP GP-PISTON 2676598 - Caterpillar

Illustration 1 g00632709
Swing Hydraulic SystemThe swing drive is equipped with a multi-disc parking brake. The parking brake is applied by spring force and released by the force of the pilot oil pressure.When the left implement control lever is activated for a swing function, swing pilot oil is sent to one end of the swing control valve in order to activate the swing function. Swing pilot oil is also sent to the resolver manifold. The swing pilot oil opens the swing parking brake pressure switch and the Automatic engine speed control (AESC) pressure switch.Opening the swing parking brake pressure switch provides a signal input to the machine control module. The machine control module then checks the ladder position switch. If the ladder is in the RAISED position, the ladder position switch is closed. If the ladder is raised, the machine control module energizes the swing parking brake solenoid valve. An energized swing parking brake solenoid valve passes pilot oil to the swing parking brakes in order to release the brakes.Note: If the ladder is in the DOWN position, the circuit is open. When the circuit is open, the swing parking brake solenoid valve remains de-energized and the swing parking brakes remain engaged.Note: If the ladder position switch has an open circuit or a short to the battery, the swing parking brake will always be applied. If the ladder position switch has a short to ground, the swing parking brake will always be disengaged when the left hand implement control lever is actuated. This could result in damage to the ladder when the ladder is down.Note: If the swing parking brake pressure switch has an open circuit or a short to the battery, the swing parking brake will always be disengaged when the ladder is up. This will allow swing drift on a side hill without actuating the left hand implement control lever. If the swing parking brake pressure switch has a short to ground, the swing parking brakes will always be engaged.Note: If the swing parking brake solenoid valve has an open circuit or a short to ground, the swing parking brake will always be applied. If the swing parking brake solenoid valve has a short to the battery, the swing parking brake will always be disengaged when the engine is running.When the left hand implement control is returned to NEUTRAL, swing pilot oil to the resolver manifold is blocked. The loss of pilot oil to the resolver manifold closes the AESC pressure switch. The loss of pilot oil also closes the swing parking brake pressure switch. The machine control module times eight seconds then de-energizes the swing parking brake solenoid valve. The de-energized swing parking brake solenoid valve returns to the closed position. Closing the swing parking brake solenoid valve shuts off the flow of pilot oil to the swing parking brakes. Shutting off the pilot oil and draining the pilot oil from the swing parking brake allows the swing parking brake return springs to apply the swing parking