Vestil HBD series - Manual (Page 5)

5
POWER UNIT'S OPERATION - continued
IN THE EVENT THAT THE CHUTE 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 chute until it is fully lowered.
• Remove any load from the chute.
• Remove the nut holding 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 PLATFORM 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:
• Lower the chute until it is fully lowered.
• Remove any load from the chute.
• Hold a rag over the cylinder's bleeder valve (it looks like a grease zerk) 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.
AIR BLEED INSTRUCTIONS FOR DISPLACEMENT-STYLE HYDRAULIC CYLINDERS
When air enters the hydraulic cylinders of the lift, it can often cause undesirable effects.
Some symptoms of air in the cylinders include:
• jerkiness or bounciness when operating the unit;
• a delay before movement begins when the "UP" control (push-button or pedal) is pressed, and;
• locking of the safety velocity fuse(s) in the lift cylinder(s) when the "DOWN" control (push-button or pedal) is pressed,
which prevents the unit from lowering.
To bleed the displacement-style cylinders:
If the cylinders are inaccessible with the unit lowered, as with our scissor lift tables, raise the platform and then lower the
legs so that they rest on the unit's maintenance props. Otherwise, if the cylinders are accessible with the unit fully lowered,
begin with the unit in the lowered position.
Locate the bleeder valve on the top end of the cylinder(s). It will look something like a grease zerk. Use a 5/16" or 3/8" wrench
to open the bleeder valve about 1/2 turn and then place a rag over it to contain the oil that will come out with the air when
it is bled. Jog the motor by pressing the "UP" control for just a second. If there is air in the cylinder, oil and air should spit
and sputter out of the bleeder valve.
Jog the motor several times (wait at least five seconds in-between) until the sputtering stops and only clear oil streams from
the bleeder valve. When you're certain all the air has escaped, close the valve(s).
Check the level of the hydraulic fluid in the reservoir. If the oil is not within 1-1/2" of the fill hole, add oil until it reaches that
level. The operate the unit and verify that it raises and lowers smoothly.