TM 5-3810-306-20
The selector valve, is located at the center of the carrier frame just forward of the rear axle. At crane start-up in travel
mode, with boom-overfront, the valve solenoids are energized, allowing rear axle oscillation, by an electrical circuit
controlled by a cam actuated roller switch mounted on the swivel. As the superstructure is rotated more than five degrees
either direction from boom-over-front-position, the switch roller rides off a cam, opening the circuit, de-energizing the
solenoids, and allowing cartridge springs to close the valve, blocking through flow and locking out rear axle oscillation.
The system is designed so that with the loss of power rear axle oscillation lockout is automatic.
Steering Relief Valve
A pressure relief valve is provided on the discharge of the steering pump to relief the pressure in the power steering
system when the pressure reaches 2500 psi (17,238/172.3). The relief valve is mounted on the front face of the frame
cross-member to rear of centerline of rotation. When the pressure in the power steering system exceeds the setpoint, the
relief valve opens to relieve hydraulic oil to the hydraulic return system.
The relief valve protects the system if pressure exceeds the designated setting. The relief valve can be pressure adjusted.
The poppet assembly is constructed with the spool area being larger than the poppet area. When pressure against the
spool reaches the pre-determined setting, the poppet assembly shifts against the springs. This opens the relief port to the
reservoir, and oil flows to the reservoir. When pressure decreases, the spring forces the poppet assembly to the neutral
position. This closes the relief port to the reservoir. A passage in the relief valve prevents a vacuum buildup within the
relief valve.
Bypass Valve Assembly
The bypass valve assembly consists of a single selector valve, air cylinder, and a three way air solenoid valve. This
assembly, controlled by a temperature switch mounted in the return manifold, allows hydraulic oil to bypass the
superstructure oil cooler fan motor when the hydraulic oil temperature is less than 111 degrees F (44 degrees C).
When the oil temperature is 120 degrees F (49 degrees C) the bypass valve is closed and the oil flows through the oil
cooler fan motor. When the temperature drops to 111 degrees F (44 degrees C), sensed by the temperature switch, the
3-way air solenoid valve is energized to move the valve spool to allow air pressure on the cylinder moves it’s piston rod
against the single selector valve to open the valve, bypassing the oil cooler fan motor.
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