5-2 Lower Mechanism: Travel Drive Unit [5] Hydraulic pressure of return oil low-pressure circuit Keep the hydraulic pressure of the return oil low-pressure circuit at 2.0 MPa or less in regard to the service life of the piston motor roller bearing and strength of other parts. Use beyond this pressure will shorten the piston motor life. Therefore, carefully consider the pressure strength when choosing pipe size, valves, etc.
[6] Pressure inside the 2nd-speed pilot pipe To select the motor speed to high or low, the switchover pressure shown on Table 4 is required. Table 4. Required Pilot Pressure for Selecting Motor Speed 2nd-speed Pilot Pressure
Low speed to high speed High speed to low speed
MPa MPa
1.5 or more 0.4 or less
To switch the speed from low to high, apply the 2nd-speed pilot pressure of 1.5 MPa or more. To switch the speed from high to low, apply a pilot pressure of 0.4 MPa or less. When running the motor at low speed in particular, the pressure leaks from the 2nd-speed control valve. This leak will flow into the 2nd-speed pilot pipe. For this reason, design the circuit so as not to increase the pressure in the 2nd pilot pipe during low-speed rotation. Increasing the pressure inside the pilot pipe may cause motor malfunction and the motor speed may switch over from low to high.
[7] Installation of self-supplied circuit The motor circuit and the pipe must be filled with oil before starting the motor. Install the self-supplied circuit on the hydraulic pressure circuit, based on careful consideration of the positional relationship of the motor and hydraulic tank. When the hydraulic motor is turned off, a trace of oil will leak from the piston motor, double counter balance valve and other valves. For this reason, if the motor is turned off for a long period of time, air will accumulate inside the motor circuit and pipe. This may cause aeration or cavitations directly after the motor starts, causing the motor to go out of control.
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