Vestil CBS Series - Manual (Page 10)

06/08 21-126-122
V ESTIL M FG . C O . 10
T HE P OWER U NIT ’ S O PERATION – CBS
The electric / hydraulic counterbalanced stacker utilizes an electric motor directly coupled to a gear-type
hydraulic pump to produce the needed fluid pressure and flow to allow the cylinder to perform the work of lifting a
palleted load or a rigid 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, which operates on a 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.
• 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 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 cylinders. These are displacement-style cylinders.
• 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
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.
When the forks are to be raised, press the “UP” pushbutton. 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 cylinder.
When the forks are to be lowered, press the “DOWN” pushbutton. The lowering valve opens, bypassing the check
valve and allowing the oil in the cylinder to return back to the reservoir through the return hose. The rate at which
the forks lower 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 the forks 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 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 to approximately 20 lb-ft of torque.
¬
If the fork carriage lowers extremely slowly or not at all (due to a cylinder’s velocity fuse closing), or if the unit is
“jerky” while raising or lowering, there is likely air in the hydraulic cylinders. To bleed the air from the system:
♦ Lower the forks until they are fully lowered.
♦ Remove any load from the forks.
♦ Job the UP pushbutton to raise the forks just a couple of inches above the floor.
♦ Hold a rag over the hose fitting at the cylinder and with a wrench loosen the hose fitting by about 1/2 turn. Oil
and air will sputter from the valve – once no air is observed, tighten the fitting.