Operation; Lifting A Load - Yale 524150797 Maintenance Manual

Special Precautions
Figure 1. Discharging Controller

LIFTING A LOAD

To raise a load, the lift button must be depressed. De-
pressing this switch will activate the pump motor. This
torque is transferred to the pump from the motor
through the motor shaft and shaft coupling.
Hydraulic oil is pumped through the system as the
pump begins to operate. A vacuum created inside of
the pump draws oil out of the reservoir through the
suction line. Air which is drawn into the reservoir
through the breather displaces the pumped oil, allow-
ing it to be sent through the system. See Figure 2 and
Figure 3. If the breather is clogged or blocked the abil-
ity of the system to lift a load will be greatly reduced.
2
1. CONTROLLER
2. POSITIVE CONNECTION
3. INSULATED JUMPER WIRES
4. 200-OHM, 2-WATT RESISTOR
5. NEGATIVE CONNECTION

Operation

As oil is pushed out of the pump, it passes through a
one-way check valve to the lift cylinder. The check
valve prevents oil from flowing back to the pump
when lifting ceases, holding the lift cylinder in the
raised position until lowered.
The piston will begin to lift the load when fluid pres-
sure acting against it is high enough to overcome the
weight of the load at rest on the forks/platform.
When the piston is fully extended to the end of its
stroke or if the load is too heavy, pressure will con-
tinue to build until the rated pressure needed to oper-
ate the relief valve is reached. When this occurs, the
relief valve, which is normally closed, is forced back
against its spring, creating a path for the fluid to flow
back to the reservoir.
1900 YRM 1506
Legend for Figure 1