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Removing the Cover
To access the internal components of the power unit, the plastic cover must be removed. First, remove the locking
pins to disconnect the dashboard from the metal frame. Open the dashboard by lifting the front lip and rotating it up to
a vertical position. Grasp the rear edges of the cover and pull them away from each other. The cover will disengage
the frame. Reinstall the cover by reversing these steps.
Cleaning the Lowering Solenoid Valve:
If the piston slowly retracts without pressing the DOWN/LOWER button, then the lowering solenoid valve might not
be closing properly. The valve should be removed and cleaned.
Unload the work surface of your unit (e.g. forks, tabletop, chute, or platform).
Completely retract the piston.
Lock out electrical power. Tag the unit "Out of Service". Turn the selector switch to the OFF position and unplug
the electrical cord from the wall socket.
Remove the cover
to access the internal components. Then, remove the nut that fastens the solenoid coil to the
valve stem.
Remove the coil and unscrew the valve from the manifold.
Inspect the valve for blockage.
Inspect O-rings and back-up washers for damage such as cuts and tears.
Submerge the valve in mineral spirits or kerosene.
Use a thin tool, such as a small screwdriver or a hex wrench, to push the poppet in and out several times from the
bottom end of the valve. The valve should move freely, about 1/16" between the closed and open positions. If the
poppet sticks, examine the valve stem to determine if it is bent. Replace the valve if the poppet doesn't move freely
after cleaning.
Remove mineral oil/kerosene from the valve with compressed air.
Confirm that the poppet freely moves in and out.
Inspect the bottom of the valve cavity in the manifold for foreign matter.
With the thin tool, press the middle of the flow control spool, which is located in the bottom of the cavity. It should
move up-and-down smoothly.
Reinstall the valve in the manifold. Tighten it with a torque wrench to 20 lb∙ft.
Bleeding Air from Hydraulic System
If the piston retracts very slowly or does not retract at all when the DOWN/LOWER button is pressed, air might be
caught in the cylinder. Air can cause the velocity fuse to close. When the velocity fuse is closed, the piston will not
retract. To correct this issue, bleed air from the system. A bleeder screw is located at the top of each cylinder. Study
the appropriate "Exploded view" in the owner's manual for your product to locate the bleeder screw. The bleeder
screw includes a hose fitting for a small diameter hose. By attaching a hose to the screw, any oil that escapes during
the bleeding process can be directed into a container for proper disposal.
Unload your unit.
If your product includes a maintenance stop, move it into maintenance position. Push the DOWN/LOWER button
until the work surface is entirely supported by the stop.
Locate the bleeder valve located at the top of the cylinder (it looks like a grease zerk; see the corresponding
"Exploded View" in the owner's manual for your product). Hold a rag over the valve. Open it about a half turn with a
wrench (turn the hex until air begins to escape). Oil and air will sputter from the valve.
Jog the motor a few times by briefly pressing and releasing the UP/RAISE button. If air continues to escape from
the bleeder valve, jog the motor several more times. Wait at least a few seconds between jogs.
Close the valve once air no longer is heard or seen bubbling out of the valve. Just a clear stream of oil should be
seen flowing from the bleeder valve.
Remove the cover
from the modular power unit. Check the oil level in the reservoir. If the surface of the oil is lower
than 1 to 1½ in. below the fill port, then add oil. Use anti-wear hydraulic fluid with a viscosity grade of 150 SUS at
100°F (ISO 32 @ 40°C) like AW-32 or Dexron transmission fluid.
Written Record:
Before putting your product into regular service, make a written record that describes the appearance and function
of the modular power unit.
writing. Record the oil level in the reservoir by marking it in a few places with a permanent marker. Describe the
electrical connections. Replace the cover and turn on the power unit. Use the hand control to extend and retract the
piston (raise and lower the tabletop/forks). Describe the sound of the power unit as the piston extends and retracts.
Indicate whether the piston extends/retracts smoothly.
Table of Contents
Rev. 11/27/2018
[Refer to
MPU Assembly
:
Remove the cover
and photograph the internal components. Describe their appearance in
Copyright 2018 Vestil Manufacturing Co.
diagram at the top of p. 18]
[Detail View
E, item 7; manifold port RV]
MPU-AC GEN2, MANUAL
Page 19 of 23
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