Vestil ZLTT series - Manual (Page 12)

08/04
V ESTIL M FG . C O ./T&S E QPT . C O . 12 of 16
T HE POWER UNIT ’ S OPERATION -- M ODEL ZLTT
The electric / hydraulic zero-clearance lift-and-tilt utilizes an electric motor directly coupled to a gear-type hydraulic
pump to produce the needed fluid pressure and flow to allow the cylinders to perform the work of lifting and tilting the
platform.
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.
o Important parts of the power unit include:
• The electric motor. Motors are available for operation on single- or three-phase AC supplies (all are dual-voltage
capable).
• The gear pump. Its shaft is coupled directly to the shaft of the electric motor. Several displacements are available,
depending on the motor horsepower used.
• The check valve. Its purpose is to prevent the backflow of fluid through the pump. In this way it allows the platform 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 develop more than 3,000 psi.
• The lowering solenoid valve. This is an electrically-operated cartridge valve. It contains a screen to keep contaminants
from entering the valve.
• The pressure-compensated flow control spool. This regulates the fluid flow back to the reservoir when the valve opens.
It allows the platform to always lower at the same rate regardless of whether there is a load on the platform or not.
Several sizes are available.
• The hydraulic lifting and tilting cylinders. 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 platform from collapsing down. The platform will remain stationary until
pressure 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.
o When the platform is to be lifted or tilted, press one of the “RAISE” pushbuttons. 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 pressurized oil through the check valve and out to the lift or tilt cylinders.
Releasing the pushbutton at any point will stop the lift or tilt motion, and the platform will hold at that height and angle
indefinitely.
An upper travel limit switch turns off the motor when the platform is at its full lift height or tilt angle.
o When the platform is to be lowered, press one of the “LOWER” pushbuttons.
♦ The lowering valve opens, bypassing the check valve and allowing the oil in the cylinders to return back to the reservoir
through the return hose. The rate at which the platform lowers is regulated by the internal pressure-compensated flow
spool.
Releasing the pushbutton at any point will stop the lowering motion, and the platform will hold at that height and angle
indefinitely.
o In the event that the platform creeps down slowly after releasing a “LOWER” control, it will be necessary to remove the
lowering cartridge valve (whichever is applicable) for inspection and cleaning, as follows:
♦ Lower the platform until it is fully lowered.
♦ Remove any load from the platform.
♦ 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 back-up 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.
o If the platform lowers extremely slowly, or not at all, a cylinder’s velocity fuse could be closing. This can be caused by
air in the hydraulic cylinder. To bleed the air from the system:
♦ Remove any load from the platform.
♦ Position the platform so that it is tilted several degrees and approximately two inches off the floor.
♦ Hold a rag over each 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.