3-22 CONTROL VALVE ASSEMBLY MAINTENANCE (CONT)
THEORY OF OPERATION (CONT)
Anticavitation Valve in Bucket Spool.
In this example, bucket spool is moved into
control valve assembly to dump the bucket. Bucket contains a heavy load and engine
is running slowly. Bucket spool stops oil flow through open center passage. When
pressure in open center passage increases, load check valve opens and lets oil flow
to A port. Oil is sent from A port to closed end of bucket cylinders.
At the same time, oil that is pushed from rod end of bucket cylinders enters control
valve assembly at B port. This oil flows into bucket spool and pushes open the pop-
pet at the bottom of the bucket spool. Oil then flows through return passage to out-
let port of control valve assembly.
Since the heavy load in the bucket is trying to push the bucket down,
is running slowly, there is not enough oil from the hydraulic pump to
ed ends of bucket cylinders full of oil. Oil pressure of oil entering
and the engine
keep the clos-
from rod end of bucket cylinders is more than the pressure in the supply passage.
The higher pressure of oil inside the bucket spool moves the poppet near the top of
the bucket spool to connect the passage in the bucket spool with the open center
passage. Return oil is added to the flow from the pump to keep the closed end of the
bucket cylinders full of oil.