The closed loop circuit for the winch drive employs a swashplate type, variable displacement piston pump (4A).
Hydraulic oil is drawn from the reservoir through the suction filter (1A) to the integral charge pump. The charge
pump provides make-up oil to the circuit as required through the check valves to the low pressure side of the circuit. It
also supplies a flow to the pressure regulating joystick (5), which operates the disc brake (23) and controls the stroke of
the piston pump. The excess flow from the charge pump above that required for these two functions passes through the
relief valve to the pump case for cooling and lubrication.
The pump case drain then runs through the thermal bypass valve (9A). At low oil temperatures this valve directs
flow around the oil cooler (9B) and back to the reservoir. This allows for a quicker warm-up of the system. As the
system warms, the bypass valve begins to open to pass some of the case drain flow through the cooler, and as the
temperature rises further all of the flow is directed through the cooler for maximum cooling. The thermal bypass valve
also incorporates a relief valve to protect the cooler from excessive pressure.
The joystick (5) is a pressure regulator which takes flow from the charge pump and sends pressure signals to the
disc brake (23) and the stroke control (4B) on the piston pump. These signals are operator-controlled through the handle
positions on the joystick. The exhaust flow from the joystick is returned to the reservoir.