Theory of Operation
propel valve (R) to turn the left propel motor (A).
Actuating the propel and arm in functions in combined
Because one pump is used to supply oil to both propel
operation (S) shifts the left (R) and right (J) propel
motors, the machine can propel straight even when the
valves and the arm II (K) and arm I (P) valves. With
arm in function is actuated in combined operation with
the valves shifted, pilot oil flow through the dig pilot
the propel function. The check valve (H) prevents back
pressure signal passage (G) is blocked by the arm II
flow through the flow combiner valve.
valve causing the pilot oil pressure in the passage to
increase. The increased pressure shifts the flow
Supply oil from the rear pump (O) flows through the
combiner valve (C), propel flow control valve (B), and
arm I valve (P) to move the arm cylinder (Q). Supply
swing park brake release valve (D).
oil from the rear pump can flow through the check
valve and propel flow control valve (B) if upstream
Supply oil from the front pump (N) flows through the
pressure is higher than pressure in the flow combiner
right propel valve (J) to turn the right propel motor (I)
as well as through the flow combiner valve (C) and left