Theory of Operation
SWING MOTOR MAKE-UP VALVE OPERATION
pressure on the other side of the motor until cavitation
While stopping the swing function the control valve
starts. When cavitation starts the make-up poppet (C)
spools go to neutral and the lines to inlet ports (D) at
is pushed open by the return oil in the make-up oil
the swing motor are blocked at the control valve.
port. The return oil flows in and prevents cavitation.
Because of the inertia of the upperstructure the oil
The make-up oil port is connected to the return
pressure in one side of the swing motor becomes high.
passage in the control valve. The return oil pressure is
For a few seconds the motor acts like a pump. The
maintained by the restriction valve located downstream
relief poppet in the crossover relief valve opens to
of the oil cooler.
relieve the high pressure oil to the make-up oil port
Because the lines to the motor are blocked the
continued rotation of the upperstructure lowers the