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Model 6210 Maintenance Manual Lift/Lower System
The lift/lower system consists of an electrically operated hydraulic pump assembly and related components.
The hydraulic pump assembly consists of a positive displacement rotary gear pump with reservoir mounted to an adapter. A DC electric motor is mounted to the opposite side of the pump adapter. An adjustable relief valve, check valve, proportional lo wering valve, and a load-hold valve are installed within the adapter.
With the forks elevated, the load-hold valve primarily prevents any fl uid from returning to the reservoir.
Lift
When the battery is connected, the truck is ON, and the lift button pressed:
•A lift request is detected via a hall effect potentiometer, converted into a lift instruction, and transmitted via the CAN to the traction amplifier.
•Lift pump contactor (LPC) closes, applying B+ to the lift pump motor (MP) causing the lift pump to operate.
•Hydraulic fluid is drawn through the 100 micron screen in the reservoir into the lift pump.
•As the pump rotates, oil is forced out the pressure port in the adapter, through the lift hose, and to the lift cylinder. Oil can not return to the reservoir because of the closed pressure relief valve and closed proportional lowering valve.
•Hydraulic pressure in the lift cylinder raises the forks.
•The relief valve opens if the hydraulic pressure exceeds the preset limit while lifting.
Lower
Section 8.Theory of Operation
Lift/Lower System
When the battery is connected, the truck is ON, and the lower button is pressed:
•Lower signal is detected via a hall effect potentiometer, converted into the lower instruction and transmitted via the CAN to the traction amplifier.
•Proportional lowering valve (SOL2) and load-hold valve (SOL1) opens.
•Hydraulic fluid in the lift cylinder returns to the hydraulic reservoir through the proportional lowering valve and the load-hold valve. The lowering speed is regulated by the proportional lowering valve.
•The forks lower.
Publication: 1146947, Revised: 12 Jan 2017 8-7
