TRAVEL CIRCUIT OPERATION PILOT VALVE CONTROL PISTON TRAVEL MOTOR R/G R/G Ps Pm1 Pm1 Pm2 P1 P2 T1 P1 P2 T2 dr3 Pk OVERLOAD RELIEF VALVE COUNTER BALANCE VALVE TURNING JOINT TO/FROM MAIN CONTROL VALVE RD21073HS27 Valves are provided on travel motors to offer the following functions. 1) COUNTER BALANCE VALVE When stopping the motor of slope descending, this valve to prevent the motor over run. 2) OVERLOAD RELIEF VALVE Relief valve limit the circuit pressure below 365 kgf/cm 2 to prevent high pressure generated at at time of stopping the machine. Stopping the motor, this valve sucks the oil from lower pressure passage for preventing the negative pressure and the cavitation of the motor. 3-21