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

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102-4 VERSALIFT VST-9000-I-E
THEOR
Y
OF OPERA
TION
TRUCK IGNITION SWITCH - The current used
when operating the start/stop control comes from
the truck ignition system. The key must be in the
ignition and turned to the “Run” position before
current is available to operate the electrical system.
TOGGLE SWITCH - The single-pole, two-position
toggle switch is mounted on the truck dash board.
RED DASH LIGHT - The red 12 volt dash light
indicates when the master control system is
activated.
OPERATION THEORY OF THE MASTER
CONTROL
The master control provides a toggle switch on the
truck dash to energize and de-energize the start/
stop system.
With the master control toggle switch activated and
the ignition switch in the “Run” position, current
fl ows from the ignition switch through a 20 amp
fuse to terminal 2 on the toggle switch. Through
the toggle switch current fl ows from terminal 2 to
terminal 3; from there current fl ows to terminal 7
on the terminal block, located in the ELECTRICAL
BOX ASSEMBLY. In addition, current fl ows from
terminal 3 on the toggle switch to the dash light.
The dash light will illuminate as current fl ows
through it to a ground.
With the master control toggle switch deactivated,
there is no electrical current fl ow to the dash light or
terminal 7, on the terminal block. The truck ignition
system will function normally.
START/STOP CONTROL COMPONENTS
Dash Push-button Control - This is a spring-
loaded, push-button control that can be used by
ground personnel to start or stop the truck engine
when the master control system is activated.
Start Relay - The 12 volt, single-pole, start relay
is mounted in the electrical box and is normally
in the open position. When activated, the start
relay connects the truck battery to the truck starter
solenoid.
Stop Relay - The single-pole stop relay is mounted
in the truck engine compartment and is normally in
the closed position. When the stop relay is activated
the ignition circuit and the start relay control circuit
are broken and the engine stops.
of them now. It is on the same side of the check
valve as it’s spring.
The combination of the oil and the spring holds
the check valve fi rmly on its seat, blocking this
passage. The oil also pushes against the backside
of the piston, the side opposite the spring. The oil
tries to push the piston off its seat by compressing
the spring. Normally, the load-induced pressure
of the trapped oil is not suffi cient to overpower the
spring and push the piston off its seat. Thus, the
oil remains trapped. This is what produces the
holding action, which prevents the booms from
creeping down or free falling should hydraulic lines
be damaged.
To release this trapped oil, hydraulic oil pressure
must be applied to the pilot piston to push it off
its seat. This pilot pressure is obtained from the
third passage for incoming oil. The combination
of the pilot pressure and the trapped oil pressure
overpowers the spring, pushes the piston off its
seat, and allows a controlled fl ow of oil out of the
cylinder returning to the control valve and back into
the reservoir.
As mentioned before, normal load induced
pressures are not adequate to overpower the spring
that acts on the piston. However, excessively
high pressures such as those generated from the
thermal expansion of the oil will open the piston
suffi ciently to relieve this pressure.
The retract pressure of the upper and lower boom
cylinder is limited to 1000 psi, by an integral relief
valve, to minimize forces if the booms are over-
stowed.
HYDRAULIC PLATFORM LEVELING - The
hydraulic platform leveling system consists of a
master/slave cylinder combination with connecting
hoses. As the outer/inner boom is raised or
lowered hydraulic oil is forced from the master
cylinder through the hydraulic lines to actuate the
slave cylinder. Counterbalance valves on the slave
cylinder prevent platform movement in the event of
hydraulic leveling hose failure. Leveling controls
are included at the upper and lower controls for
leveling adjustment.
ELECTRICAL SYSTEM
The electrical schematics will aid in understanding
the electrical system. Refer to the specifi c option
schematics. Descriptions of the major components
in the electrical system are given below.