FLASHING 8C2719 - Caterpillar

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Medium pressure manifold (1) Cab riser control valve (2) Medium pressure manifold (3) SolenoidsThe hydraulic cab riser system allows the cab to be raised and lowered with hydraulic cylinders. The cylinders for the cab riser are controlled by cab riser control valve (1). Oil from the pilot pump flows to medium pressure manifold (2). Solenoids (3) mounted on control valve (1) control the spool inside the control valve. The spool controls the flow of medium pressure oil to the hydraulic cylinders. Electronic switches that are located on the joystick are used to control the solenoids (3) .Note: A step safety switch that is located inside the left rear access door disables the cab riser if the access door is open.Operation of Hydraulic Cab Riser
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Hydraulic cab riser schematic (1) Cab riser control valve (2) Medium pressure manifold (3) Solenoids (4) Cab riser cylinders (5) Manual lowering valves (6) Pilot pumpCAB RAISE Function
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Hydraulic cab riser partial schematic (CAB RAISE) (1) Cab riser control valve (3) Solenoid (4) Cab riser cylinders (6) Pilot pump (7) Valve (8) Line When the operator moves the switch to raise the cab, electrical current energizes solenoid (3). The spool in control valve (1) shifts. Pilot oil flows to valves (7) and then flows to the rod end of cab riser cylinders (4) .When pilot oil flows into the rod end of cab riser cylinders (4), the oil flow causes the cylinder rod to retract. Return oil from the head end of cylinders (4) flows through line (8) to the hydraulic tank. The cab raises.
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Acceleration and deceleration of the cab riser are electronically controlled in order to provide a smooth start and stop. In addition, a position sensor provides a signal for an electronic speed reduction in the extreme upper position of the cab and the extreme lower position of the cab. During any of these conditions, the cross section of the directional control valve is reduced by changing the current to the solenoids.CAB LOWER Function
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Hydraulic cab riser partial schematic (CAB RAISE) (1) Cab riser control valve (3) Solenoid (4) Cab riser cylinders (6) Pilot pump (7) Valve (8) Line When the operator moves the switch to lower the cab, electrical current energizes solenoid (3). The spool in control valve (1) shifts. Pilot oil flows to valves (7). Pilot pressure shifts the spools inside valves (7). The pilot oil also flows into the head end of cylinders (4). The oil in the rod end of cylinders (4) flows to the return system.Pressure oil from the head end of cylinders (4) flows through line (8) to the hydraulic tank. Oil flows from the rod end of cylinders (4) to the return system. The oil flow causes the cylinder rod to extend. The cab lowers.Note: The mass of the cab is used to extend cylinders (4). Pressure oil is not needed to lower the cab. The oil from the rod end of cylinders (4) is restricted in flowing to the return system.