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HYDRAULIC CIRCUIT
CASE TRAINING CENTER
AUGUST 2000
Straight Travel Circuit
This section describes the case where travel and boom-up operations are conducted at the same time.
The hydraulic oil entered the pilot pump from Ps1, which is connected to the tank via travel spool, is shut off
by changing over of the travel spool.
In addition, changing over of the spool for boom (2) shuts off the branch channels from Ps1 via all spools
for the attachments (Boom, Arm, Bucket and Swing) connected to the tank. Therefore, the hydraulic oil
from the pilot pump entered at Ps1 can find no place to go and the circuit pressure raises up to the original
pressure (3.9 MPa). This original pressure acts on the pilot chamber of the straight travel valve and the
straight travel valve changes over. Due to the changing over of the straight travel valve, it becomes
possible for RL to drive the travel mechanism and for PR to drive the attachments. For travel, the left and
right pressures are equal because one pump drives the left and right motors, thus straight travel is realized.
Additionally, extra hydraulic oil from PR is supplied through the check with travel combination limit to the
travel side, and speed reduction is limited to the minimum.
It is the same as above when the upper actuators other than boom and travel are operated at the same
time.
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