Hyundai HX130LCR Manual page 113

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Table of Contents

Holding operation

When the control valve is at neutral position, VA and VB ports are connected to the tank, and the

spring (33) located on both spool ends holds the spool (31) at central position.

Therefore, the passages from VA to MA and VB to MB are closed, which result in closing MA

and MB ports connected to hydraulic motor.

Since the passage to parking brake is connected to the tank line, the brake cylinder pressure is

equal to the tank pressure and the brake is applied by the springs. Thus, the rotation of the motor

is mechanically prevented.

If external torque is exerted on the motor shaft, the motor would not rotate as usual by this

negative parking brake.

In case the brake should be released for some reason, pressure is built on MA or MB port. But,

due to oil leakage inside hydraulic motor or so, high-pressure oil escapes from the closed circuit

and motor rotates a bit. So, the cavitation tends to occur in the lower pressure side of the closed

circuit. Then, the check valve, built in the spool (31), operates to avoid the cavitation and opens

the passage from VA to MA or from VB to MB. Then the oil equivalent to the leakage is sucked

from the tank line to the closed circuit.

Troubleshooting