TM 9-2350-256-34
INTERMEDIATE MAINTENANCE
RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
AUXILIARY HYDRAULIC SYSTEM MAINTENANCE
INITIAL SETUP:
References
TM 9-2350-256-10
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 APU. 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 boom, spade, main winch, and hoist winch is controlled by the same control valves
as used in the main hydraulic system. The operation of the refuel-defuel system is controlled by a manually operated four-way
selector valve and an adjustable flow regulator. Description of operation of the basic circuits in the auxiliary hydraulic system
will be found below. Schematic diagrams of the auxiliary hydraulic system idling, the main winch inhaul and payout, the hoist
winch raise and lower, the hoisting boom raise and lower, the spade raise and lower, the refuel-defuel pump, and the impact
NOTE
Refer to TM 9-2350-256-10 for operating instructions for the boom, winches, spade, refuel-defuel, and
impact wrench system.
With the APU operating, the system selector valve in the MAIN position, and the APU emergency winch control valve in the
CLOSED position, oil is drawn from the hydraulic reservoir (port no. 243) into the pump (port no. 63), and the pump discharges
low pressure oil (port no. 64) to the system selector valve (port no. 48) and returns to the reservoir (port no. 236). The above
valve lever positions are used when the APU generator is being used to charge the batteries.
With the system selector valve in the AUXILIARY position, and the APU emergency winch control valve in the OPEN position,
hydraulic pressure is directed to the main winch combination control valve (port nos. 12 and 13), and returns to the reservoir
(port no. 237). 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 valve, is directed to 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) which controls the movement of the cable level winder.
With the system selector valve in the AUXILIARY position, and the APU emergency winch control valve in the OPEN position,
hydraulic pressure is directed to the main winch combination control valve (port nos. 12 and 13) and returns to the reservoir
(port no. 237). With the main winch control valve placed in the PAYOUT position, the pilot pressure (port nos. 15 and 16) tends
to equal pump discharge pressure and is directed to both ends of the pilot-operated directional control valve (port nos. 8 and
10) in the main winch combination control valve. The ends of the directional control valve differ in size, the larger end at port
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