HYDRAULICS – CX130/CX160
5 - 16
CX EXCAVATORS
SWING
Swing Operation
1) The swing holding brake prevents the upper structure from drifting on a hillside until
the swing hand control is moved or either main pump pressure is raised to +2050 psi.
2) Pilot oil from the swing brake solenoid valve releases the swing brake.
3) The machine uses flow from one pump during swing operation.
4) The upper structure is braked hydraulically before the swing holding brake is applied.
Swing, Brake off Operation
When the swing hand control is operated, pilot pressure is directed to the swing control spool
in the main control valve. The control spool shifts and sends pump2 oil to the swing motor for
left or right swing. At the same time a pressure switch in the swing pilot circuit is closed. The
pressure switch sends a signal to the controller which turns OFF the swing-brake solenoid
valve, the valve shifts and sends full pilot pressure (550/600 psi) to the swing brake to
release the brake. The swing pressure switch is located in the swing shuttle valve mounted
behind the cab. The swing brake solenoid is part of the six-solenoid valve located in the
pump compartment.
When ever either main pump pressure reaches approximately 2050 psi the controller will
release the swing brake by turning OFF the swing-brake solenoid. This is done to protect the
upper structure from side loading that occurs while digging. The controller monitors pump
pressure by way of pressure transducers located at each main pump.
Swing Braking Operation
When the swing control is returned to neutral, the centering springs of the swing control
spool shift the spool to neutral. The oil flow from pump2 (rear pump) to the swing motor is
diverted and the supply and return ports of the swing motor are blocked. The inertia from the
swing movement will cause a pressure spike in the blocked return side of the motor. To
prevent spike pressure damage, a built-in crossover relief valve is opened and oil flows
through a make-up check valve to the supply side of the motor or to the reservoir. When the
pressure is equalized between the return and supply ports the motor acts as a brake and
swing motion is stopped. Between the time the supply and return ports are blocked by the
control spool and the crossover relief opens, oil from the main return circuit is available at
port Mu of the swing motor to pass through the make-up check valve to the supply side of the
motor.
Five seconds after the swing lever is returned to neutral (swing pressure switch opens), the
swing brake is applied when the controller sends an (24v) signal to energize the swing brake
solenoid. The valve shifts and dumps the brake release pressure back to tank. The brake is
spring applied and hydraulically released.
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