I have to question that. If you look at the supplied page above it shows the travel relief pressure at 5,130 PSI on one pump at a time while the boom up and arm in is at 5,400 PSI and the boom down arm out is at 5,690 PSI. That would indicate to me that the main relief is already higher than the settings of the travel circuits.
Hi Mr. John C,
It's an ambiguity of the Hitachi''s technical documentation!!
I would like to note that there are 03 kinds of "RELIEF" pressure (as you can see in the picture):
1/-
MAIN RELIEF VALVE SET PRESSURE (02 MAIN relief valves on Main control valve): set for all actuators.
2/-
RELIEF PRESSURE (usually named that PORT RELIEF VALVE, they are installed on hydraulic motors ): set for SWING & TRAVEL. Their values should be
equal to or higher than main relief pressure values.
3/-
OVER-LOAD RELIEF VALVE SET PRESSURE (usually named that PORT RELIEF VALVE, they are installed on main control valve also): set for BOOM _ ARM _ BUCKET. Their values should be
higher than main relief pressure values.
You also can see that
MAIN RELIEF PRESSURE MAX. is
4980 psi for BOOM & ARM and
5160 psi for BUCKET, is it right?
And
TRAVEL pressure MAX. is 4980 psi for both travel and
5130 psi for 01 travel.
That means
TRAVEL PRESSURE MAX. equal to MAIN PRESSURE RELIEF (5160 psi and 5130 psi is a negligible error
).