TM 9-2350-256-34-2
discharge pressure (port no. 52) is also directed to the level winder valve (port no. 50) which controls the direction of
movement of the cable level winder.
d. Main Winch-Inhaul (fig. FO-3). With the main winch control valve placed in the INHAUL position, the hydraulic
pressure at the large area end of the pilot-operated directional control valve in the main winch combination control valve,
is directed to the tank return (port no. 10). The pilot pressure is directed to one end (port no. 8) of the pilot-operated
directional control valve, positioning the valve to direct pump pressure to one side of the main winch motor (port no. 17)
and causing the motor to drive the main winch in the INHAUL direction. The hydraulic pressure in the brake cylinder is
ported to tank return, causing the brake cylinder springs to engage the brake; and the brake ratchet and pawls are
available for instant braking. Pump pressure is also being directed to the level winder valve (port no. 50).
e. Hoist Winch-Lower (fig. FO-4). With the hoist winch control valve placed in the LOWER position, pilot pressure is
directed to both ends of the pilot-operated directional control valve (port nos. 19 and 24) in the hoist winch combination
control valve. The differential across the directional control valve, due to the difference in size, positions the valve
directing the pump pressure (port No. 57) to one side of the hoist winch motor (port no. 17). The hoist winch motor then
drives the hoist winch in the LOWER direction. Pilot pressure is directed to the hoist winch brake cylinder, overcoming
the spring force, causing the brake band to expand, and allowing the brake drum to rotate.
f. Hoist Winch-Raise (fig. FO-5). With the hoist winch control valve placed in the RAISE position, the hydraulic
pressure at the large end (port no. 19) of the pilot-operated directional control valve in the hoist winch combination
control valve is directed to tank return. The pilot pressure is directed to one end of the pilot-operated directional control
valve (port no. 24), positioning the valve to direct pump pressure to one side of the hoist winch motor (port no. 18) and
causing the motor to drive the hoist winch in the RAISE position. The brake cylinder pressure is directed to tank return,
allowing the brake cylinder springs to compress the brake band around the winch brake drum, and providing instant
braking through the brake drum ratchet and pawls.
g. Hoisting Boom-Forward (fig. FO-6). With the manually operated directional control valve, in the boom combination
control valve, placed in the FORWARD position and at the same time placing the boom safety valve in the STOW
position, pilot pressure is blocked at both valves. (port nos. 31 and 39). Pump discharge pressure (port no. 34) is
directed to the boom cylinders, extending the piston rod and raising the boom. The stayline cylinder pistons are retracted
mechanically into the stayline cylinders by the crankarms and the fluid behind the piston is forced out to tank return (port
No. 62).
h. Hoisting Boom-Retract/Stow (fig. FO-7). With the manually operated directional control valve, in the boom
combination control valve, placed in the RETRACT/STOW position, and at the same time placing the boom safety valve
in the STOW position, pilot pressure is blocked at both valves (port nos. 31 and 39). Pump discharge pressure is
directed to one end of the boom (port no. 61) and stayline cylinders (port no. 62), the opposite cylinder ends are ported to
tank return (port nos. 61 and 62), causing the boom cylinders to retract and the stayline cylinders to extend.
i. Spade--Raise (fig. FO-8). With the manually operated directional control valve, in the spade combination control
valve, placed in the RAISE position, pilot pressure is blocked at the valve (port no. 30). Pump discharge pressure is
directed to one end of the spade cylinders (port no. 59), and the opposite end (port no. 60) is ported to the tank return,
causing the cylinder rod to retract and raising the spade.
j. Spade-Lower (fig. FO-9). With the manually operated directional control valve, in the LOWER position, pilot
pressure is blocked at the valve (port no. 30). Pump discharge pressure is directed to one end of the cylinders (port no.
60) and the opposite end (port no. 59) is ported to the tank return, extending the cylinder rod causing the spade to lower.
2-11. Maintenance and Operation of Auxiliary Hydraulic System
a. General. The auxiliary hydraulic system powers and controls the hoisting boom, spade, main winch and hoist winch
when the main engine is inoperative. The auxiliary hydraulic system also powers and controls the refuel-defuel pump
and the hydraulic impact wrench. The auxiliary system power is supplied by a fixed-displacement, gear-type hydraulic
pump which draws fluid from the hydraulic oil tank and is driven by the auxiliary power unit. The auxiliary hydraulic
pump output is determined by the governed speed of the power unit engine. Any internal leakage through the hydraulic
cylinders or valves is returned to the hydraulic oil tank by the tank return circuit. The operation of the hoisting
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