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