Main winch and hoist winch control valves

Figure 1-16. Hydraulic subplate assembly right front view

Figure 1-17. Combination control valves-installed view

TM-9-2350-256-34-2 Recovery Vehicle Full Tracked; Medium M88A1 (NSN 2350-00-122-6826) Manual
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TM 9-2350-256-34-2 passages to inlet or outlet ports of the subplate and the attached control valves. 1. Main winch and hoist winch control valves. When the valve is in the spring-centered HOLD position, pilot pressure is directed through the valve to the tank return. Also, pressure is bled from the winch combination control valve to the same tank return. Manually placing the valve in the PAYOUT or LOWER position directs the pilot pressure to the winch combination control valve and the brake cylinder and closes the port opening to the tank return. Moving the valve to the INHAUL or RAISE position blocks the pilot pressure to the control valve and bleeds the pilot pressure from the winch combination control valve and brake cylinder, through the control valve, to the tank return. 2. Boom combination control valve. When this control valve is in the spring-centered HOLD position, main pump pressure is blocked and pilot pressure is directed to the tank return. Manually placing the valve in the FORWARD position cuts off pressure and directs main pump pressure through a one-way check valve and a flow restriction to the boom-actuating cylinders. Pressure from the opposite side of the cylinders is directed by the valve to the tank return. If maximum pressure is exceeded, the relief valve opens and bleed: off pressure to the tank return. Placing the valve in the RETRACT/STOW position cuts off pilot pressure and directs main pump pressure through a one-way check valve and a flow restriction to the boom-actuating cylinders and the stayline cylinders. Pressure from the opposite end of cylinders is ported through the valve to the tank return. The maximum pressure relict valve opens if preset pressure is exceeded. 3. Boom safety control Valve. When the valve is in its spring-loaded LIVE position, pilot pressure is directed to the boom limit valves. Manually placing the valve in the STOW position cuts off pilot pressure to the boom limit valves. 4. Power control valve. Manually placing the valve in the ON position allows pump pressure to pass through the valve to the transmission clutch cylinder. Moving the valve to the OFF position. blocks the pump pressure and bleeds the oil pressure from the clutch cylinder, through the valve, back to the transmission crankcase return line. 5. System selector control valve. When the manual selector control valve is in the center or MAIN position, main hydraulic pump pressure is directed to the spade combination control valve and the boom combination control valve. Pump pressure to the refuel pump motor control valve impact wrench is blocked and any residual pressure from the auxiliary pump is bled to the tank return. Moving the valve to the AUXILIARY position, directs auxiliary pump pressure to the spade combination control valve and the boom combination control valve. The port opening from the main pump is closed. and residual pressure from the refuel pump motor control valve and impact wrench line is allowed to flow past the valve to the tank return. Placing the valve in the REFUEL position permits the use of main pump pressure and auxiliary pump pressure simultaneously for different operations or the use of just auxiliary pump pressure for refueling or use of the impact wrench. Main pump pressure is directed to the spade and boom combination control valves and auxiliary pump pressure is directed to the refuel pump motor control valve and the impact wrench. 6. Auxiliary power unit (APU) emergency winch control valve. When this valve is in the OPEN position, the auxiliary hydraulic pump directs pressure oil to the hoist winch combination control valve and the main winch combination control valve. (For emergency No Load operation of the winch cables). Hydraulic pump pressure is blocked when this valve is in CLOSED position. (4) Combination control valves (fig. 1-17). Four combination control valves are utilized in the main hydraulic system. Two of these valves are manually operated to combine control, check, and adjustable relief for boom and spade operation. The boom combination control valve is subplate mounted to the control panel, and the spade combination control valve is subplate mounted to the cab front wall. The other combination control valves are pilot operated and combine pressure and directional control with adjustable relief for the winches. Change 1 1-19

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