TM 9-2350-256-34
0003 00
Boom Safety Control Valve
The boom safety control valve (Figure 12) is a manually operated, two-position, single-flow path valve, and is spring-loaded
to the LIVE or open position. 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.
Power Control Valve
The power control valve (Figure 12) is a manually operated, two-position, directional flow valve. The valve is held in its selected
position by an internal mechanical detent. 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.
System Selector Control Valve
The system selector control valve (Figure 12) is a manually operated, three-position, directional, combination control and relief
valve. It is held in its selected position by an internal mechanical detent. 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. 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.
APU Emergency Winch Control Valve
The APU emergency winch control valve (Figure 13) is a manually operated, two-position (open and closed), single-flow
path, ball 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 the closed position.
Combination Control Valves
Four combination control valves (Figure 14) 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 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.
0003 00-15