CARGO HANDLING SYSTEM
THEORY OF OPERATION
The hoist system can be operated from the cockpit
or from any of three locations in the cabin. System
operation is identical regardless of which location is
used. Operation described here is from the cockpit
overhead panel, with the winch shifting lever at
RESCUE. The control locations in the cabin can be
used when the HOIST MASTER switch on the cockpit
overhead panel is at REMOTE.
Placing the HOIST MASTER switch to PILOT
connects 28-volt dc from the bus to the
spring-loaded center-off HOIST rotary switch.
The rotary switch has a set of contacts that close
whenever the switch is off center. When off
center, these contacts energize the winch brake
control valve solenoid. When energized, this
solenoid directs pressurized hydraulic fluid to
release the winch brake and to the P (pressure)
port of the winch control valve.
Rotating the HOIST switch to OUT energizes
the winch control shutoff valve solenoid. At the
same time, current flows from the rotary switch
to energize the winch control valve OUT solenoid
thru the out-limit switch on the winch. Hydraulic
fluid from the C1 port of the winch control
valve flows thru the pressure reducing valve.
This reduces the pressure to 750 psi before it
reaches the OUT port of the winch motor. This
pressurized fluid operates the hydraulic motor to
reel out the cable. The fluid returns to the system
through the IN port of the winch motor to the
winch control valve. A relief valve between the
hoist in line and system return protects the winch
motor case shaft seal from high pressure.
When the HOIST switch is released to OFF, the
winch control shutoff valve and the winch control
valve circuits open. The winch control valve and
shutoff valve return to the deenergized position.
This stops fluid flow to the winch motor, to the
brake release line, and the winch control valve.
The winch control shutoff valve then directs fluid
from the brake release line to the utility hydraulic
system return line and the spring-loaded brake is
Rotating the HOIST switch to IN closes the
contacts that complete the winch control shutoff
valve solenoid circuit. It also moves the wiper of
the rotary switch into contact with the IN portion
of the switch. Current flows through the wiper
arm to the IN solenoid of the winch control valve,
through the overload limit and in-limit switches
on the winch, and the cable cutter plug. The
IN solenoid positions the winch control valve to
direct fluid through the C2 port of the valve, to the
IN port of the winch motor. The pressurized fluid
operates the hydraulic motor to reel in the cable.
The fluid returns to the system through the OUT
port of the winch motor, the pressure reducer,
and the return port of the winch control valve.
When the CABLE CUTTER switch on either the
hoist control panel or the operators grip is ON,
power from the 28-volt dc bus is connected
to the cable cutter cartridge. In this condition,
operation of the cable cutter from either the
cockpit or cabin is independent of the HOIST
Limit switches prevent winch overloading, stop
winch OUT operation when the cable is extended
150 feet, and stop winch IN operation when
the cable is extended 28-1/2 feet in the rescue
mode or extended 3 feet in the cargo mode.
An overload limit switch opens the circuit when
the load on the cable exceeds 3,100 to 3,200
pounds when the winch is operated in the reel-in