Versalift VST-9000I-E100, Service And Installation Manual

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102-3 VERSALIFT VST-9000-I-E
THEOR
Y
OF OPERA
TION
The outrigger controls consist of two, four-way
control valves connected in series. A relief valve
is integral to these control valves. Hydraulic oil is
directed to either end of a double-acting hydraulic
cylinder, which extends or retracts the outriggers.
A lock valve or double pilot operated check valve
is mounted on each outrigger cylinder, blocking
undesired fl ow out of each end. When the four-way
control valve is actuated, pressure is applied to one
end of the cylinder and to a pilot piston that opens
the check valve allowing fl ow out of the other end.
Flow now extends or retracts the outrigger cylinder
as desired. A thermal relief valve is incorporated
into the lock valve that allows excessive pressure
created by thermal expansion to bypass the check
valve.
The optional tool circuit control includes a two-
position selector valve. Ground-level hydraulic
tools can be operated when the ground controls are
engaged and the tool selector is actuated.
When the ground controls are selected, oil will
circulate through the control valves and back to
the reservoir because they are open center valves.
Open-Center valves help warm-up the hydraulic oil
in cold weather.
ROTARY JOINT - A rotary joint is mounted between
the turret and pedestal, To provide hydraulic fl ow
to the lift and allows continuous rotation of the lift.
The rotary joint consists of a cylindrical case, which
houses a spool. The case is bolted to the pedestal
and the spool is fastened to the turret.
Oil from the pump enters port 2 of the spool, fl ows
up a drilled passage in the spool, and into a groove
which encircles the surface of the spool. Oil fl ows
along the groove until it comes to the outlet port 2
in the case, wherever it is at that particular time.
Because the case outlet moves along the groove
as the lift rotates, oil fl ows uninterrupted out of the
case port. Return oil fl ows through port 1 and 3 of
the case, along the groove in contact with respective
port and then out each respective port of the spool
on its way back to the oil reservoir. Since all of the
relative motion takes place between the spool and
the case, continuous rotation is possible.
LOWER CONTROLS - The lower controls are
located on the console at the deck. The platform
override control is the fi rst section of the control
valve. When this control is selected oil is diverted
either to the upper controls or allowed to fl ow to
the second, third, fourth, fi fth, sixth and seventh
sections which control the lower boom, upper
boom, rotation, winch, platform leveling, lower
arm elevator and upper arm elevator functions
respectively. Oil is available to these sections only
when the lower controls are selected.
UPPER CONTROLS - The single stick upper
control consists of a seven-section control valve,
selector valve, and a tool/accessory valve. A single
selector valve diverts oil from the control valve to
the reservoir. This valve is used as the emergency
stop valve.
The seven-section control valve is used to operate
unit functions. The fi rst spool of this valve is used
for platform leveling. The second spool is used for
platform rotation. The third spool is used for the
lower boom function. A simple lever starts these
three functions. The fi fth, sixth and seventh spools
operate the boom functions through a specially
developed single stick package.
The fourth spool diverts the fl ow of oil, to the fi fth,
sixth, and seventh boom function spools, or to the
tool circuit. With the safety trigger released, oil fl ows
to the tool/accessory valve. With the safety trigger
activated, oil fl ows to the boom functions spools.
The tool/accessory valve operates jib extend, jib
tilt, winch, and tools. When the tool power lever is
“ON” oil fl ows to the tool, otherwise the oil returns
to tank.
BOOM AND ARM CYLINDERS AND HOLDING
VALVES
- When the valve controlling the oil fl ow to
the cylinders is actuated, the oil leaves the control
valve assembly and fl ows to the holding valve.
Where it enters three passages. A piston, spring-
loaded against its seat blocks one passage. The
incoming oil is on the same side as the spring. This
causes the piston to be pressed even tighter against
the seat, effectively blocking the passage. The oil
then fl ows through the other passage, which has
a spring-loaded check valve in it. The oil pushes
the check valve off its seat, fl ows out of the holding
valve, and into the hydraulic cylinder.
The hydraulic cylinders are double acting, meaning
both ends of the cylinder can be pressurized. In
order for the incoming oil to move the cylinder piston,
oil on the other side of the cylinder piston must be
able to escape from the hydraulic cylinder. The oil
cannot escape because the other holding valve is
blocking it. The passages in this holding valve are
identical to the ones described above, however,
the oil is trying to fl ow through the passages in the
opposite direction. The oil meets the piston and
the check valve again, both identical to those in the
holding valve. However, the oil is on the backside