11
THE POWER UNIT’S OPERATION – TM, TMS
The electric / hydraulic pallet tilter utilizes an electric motor directly coupled to a gear-type hydraulic pump to produce the
needed fluid pressure and flow to allow the cylinder(s) to perform the work of tilting a container.
A hydraulic manifold houses the hydraulic control components, and is bolted directly onto the gear pump.
The power unit’s hydraulic components are all rated for 3,000 psi working pressure.
•
Important parts of the power unit include:
-
The electric motor operates on 12 VDC deep-cycle battery supply.
-
The gear pump. Its shaft is coupled directly to the shaft of the electric motor.
-
The check valve. Its purpose is to prevent the backflow of fluid through the pump. In this way it allows the fork
carriage to be held at a given elevation indefinitely.
-
The pressure relief valve. Its job is to open a path for fluid to flow back to the reservoir in the event that the fluid
pressure built up by the pump exceeds 3,000 psi. Thus the system cannot see more than 3,000 psi.
-
The lowering solenoid valve. This is an electrically operated cartridge valve. It contains a screen to keep contami-
nants from entering the valve.
-
The pressure-compensated flow control spool. This rests under the lowering valve, and regulates the fluid flow back
to the reservoir when the valve opens. It allows the forks to always lower at the same rate regardless of whether
there is a load on the fork carriage or not.
-
The hydraulic tilt cylinder(s). These are displacement-style cylinders. They have a bleeder valve located at their top
end to allow air to be bled from the hydraulic system.
-
The safety velocity fuse. This is a device that is installed in the cylinder’s hose port. It closes quickly in the event of a
catastrophic hose failure to prevent the fork carriage from collapsing down. The forks remain stationary until pres-
sure is reapplied to the system.
-
The hydraulic fluid. The system uses HO150 hydraulic fluid. Any anti-wear hydraulic fluid with a viscosity grade of
150 SUS at 100°F (ISO 32 @ 40°C) such as AW-32 or Dexron transmission fluid are acceptable.
When the forks are to be tilted, press the “UP” push-button. The motor turns, and in turning it spins the hydraulic
gear pump. Oil is drawn from the reservoir through the suction filter and into the pump. The pump pushes the then-
pressurized oil through the check valve and out to the tilt cylinder(s).
When the fork carriage is to be lowered, press the “DOWN” push-button. The lowering valve opens, bypassing the
check valve and allowing the oil in the cylinder(s) to return back to the reservoir through the return hose. The rate at
which the fork carriage lowers is regulated by the internal pressure-compensated flow spool.
•
In the event that the fork carriage creeps down slowly after releasing the “DOWN” control, it will be necessary to
remove the lowering cartridge valve for inspection and cleaning, as follows:
-
Lower the forks until they are fully lowered.
-
Remove any load from the forks.
-
Remove the nut holding the solenoid coil on the valve stem, then remove the coil, and then unscrew the valve from
the manifold.
-
Inspect the valve for contaminants, and the valve’s o-rings and backup washers for cuts, tears, or other damage.
-
With the valve immersed in mineral spirits or kerosene, use a thin tool such as a small screwdriver or a small 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” from closed to open position. If it sticks in, the valve stem could be bent and will need to be replaced if it
doesn’t free up after cleaning. Blow the valve off with a compressed-air gun while again pushing the poppet in and
out.
-
Inspect the bottom of the manifold’s valve cavity for contaminants.
-
Again with the thin tool, press on the middle of the flow control spool located in the bottom of the cavity. It should
move down and back up freely.
-
Reinstall the valve into the manifold, tightening the valve with approximately 20 lb-ft of torque.
•
If the fork carriage lowers extremely slowly, or not at all, the cylinder’s velocity fuse could be closing. This can be
caused by air in the hydraulic cylinder(s). To bleed the air from the system:
-
Lower the fork carriage until it is fully lowered.
-
Remove any load from the forks.
-
Hold a rag over the cylinder’s bleeder valve (it looks like a grease zirk) and open the valve about 1/2 turn with a 1/4”
or 5/16” wrench. Oil and air will sputter from the valve – once no air is observed, close the valve.
E
N
G
L
I
S
H
