3-22. CONTROL VALVE ASSEMBLY MAINTENANCE (CONT)
THEORY OF OPERATION (CONT)
Anticavitation Valve in Lift Spool.
In this example, lift spool is moved into con-
trol valve assembly to lower the loader frame. There is a heavy load in the bucket
and the engine is running slowly. The lift spool stops the flow of oil through the
open center passage. When the pressure in the open center passage increases, the
load check valve opens and lets the oil flow to the A port. Oil is sent from the A
port to the rod end of the lift cylinders.
At the same time, the oil that is pushed from the closed end of the lift cylinders
enters control valve assembly at the B port.
This oil flows through the return pas-
sage to the outlet port.
Since the heavy load in the bucket is trying to push the bucket down, and the engine
is running slowly, there is not enough oil flow from the hydraulic pump to keep the
rod end of the lift cylinders full of oil. The pressure in the return passage is
more than the pressure in the A port of the lift spool. The higher pressure in the
return passage moves the poppet in the anticavitation valve to connect the return
passage with A port.
The oil in the return passage flows to the A port to be added
to the oil from the pump to keep the rod end of the lift cylinders full of oil.