Vestil LDLT series User Manual
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THE POWER UNIT'S OPERATION - HT, LDLT
The electric/hydraulic table 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 the table load.
A hydraulic manifold houses the hydraulic control components, and is bolted directly onto the gear pump.
The power unit's hydraulic components are all treated for 3,000 psi working pressure.
Important parts of the power unit include:
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The electric motor operates on 12 VDC.
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The gear pump. Its shaft is coupled directly to the shaft of the electric motor.
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The check valve. Its purpose is to prevent the backflow of fluid through the pump. In this way it allows the table
to be held at a given elevation indefinitely.
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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 pump cannot generate more than 3,000 psi.
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The lowering solenoid valve. This is an electrically-operated cartridge valve. It contains a screen to keep
contaminants from entering the valve.
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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 table to always lower at the same rate regardless of whether there
is a load on the table or not.
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The hydraulic lift cylinder. On units with a motor or two-speed foot pump, the cylinder has a bleeder valve located
at their top end to allow air to be bled from the hydraulic system.
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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 table from collapsing down. The table remains stationary until pressure
is reapplied to the system.
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The hydraulic fluid. The system uses HO150 hydraulic fluid. Any anti-wear hydraulic oil with a viscosity grade of
150 SUS at 100°F (ISO 32 @ 40°C) such as AW 32 or non-synthetic transmission fluid is acceptable.
When the table is to be raised, press the "UP" push-button or foot switch. 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 lift cylinders.
When the table is to be lowered, press the "DOWN" push-button or foot switch. 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 table lowers is regulated by the internal pressure-compensated flow spool.
In the event that the table creeps down slowly after releasing the "DOWN" control, it will be necessary to remove the lowering
cartridge valve for inspection and cleaning, as follows:
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Lower the table entirely.
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Remove any load from the table.
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Remove the nut holding the solenoid coil on the valve stem, remove the coil, and then unscrew the valve from
the manifold.
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Inspect the valve for contaminants, and the valve's o-rings and backup washers for cuts, tears, or other damage.
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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 form the bottom end of the valve. The valve should move
freely, and 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.
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Inspect the bottom of the manifold's valve cavity for contaminants.
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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.
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Reinstall the valve into the manifold, tightening the valve with approximately 20 lb-ft of torque.
If the table lowers extremely slowly, or not at all, the cylinder's velocity fuse could be closing. This can be caused by air
in the hydraulic cylinders. To bleed the air from the system:
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Lower the table entirely.
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Remove any load from the table.
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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.