3
Hydraulic Circuit & Component Operation
To raise the deck of the table, press the
"RAISE"
button of the hand controller. This opens the air motor
supply valve and flowing air turns the hydraulic pump. Oil from the reservoir moves through the suction filter
and into the pump. From the pump, pressurized oil flows through the check valve and then enters the
cylinders.
The function of the check valve is to
restrict
oil flow
to
one direction, i.e. towards the cylinders. It
prevents oil
from flowing
back into the pump circuit when the pump stops running. This
trap
s oil in the
cylinders and maintains the desired elevation
of the deck
.
If the
weight of a
load
on the table
exce
eds the capacity of your table
,
then
a
lthough
the
"RAISE"
button
might be
pressed
the deck cannot ascend. Instead,
pressure
build
s
in the circuit between the pump
and the cylinders. This
pressure
caus
es the "ball"
(
or "poppet"
)
in the relief valve to unseat
and directs
the
pump output
to
the reservoir through the return pipe
rather than to the cylinders.
T
o lower the
deck
, press the
"LOWER"
control
button. This opens a hydraulic
dump
valve. The
poppet in the solenoid valve unseat
s
and oil
flow
s from the cylinders through the flow control valve, return
filter, solenoid valve,
and the
oil return pipe
to
the reservoir.
The flow control valve controls the lowering speed of the table. It is preset and cannot be changed.
Releasing the
"LOWER"
control
button
deenergize
s
the solenoid
and
clos
es
the valve poppet. This
prevents oil from returning to the reservoir and
consequently
the cylinders stop retracting. The
deck
will
maintain
its
elevation.
Cartridge Valves
The lowering valve, as discussed above, is of cartridge construction and is virtually maintenance free.
If a malfunction occurs, refer to the trouble shooting section.
To clean the cartridge valve:
1.)
Use a thin tool to push the poppet in from the bottom to open the valve.
2.)
Repeat several times while valve is immersed in kerosene or mineral spirits. Blow the valve
dry.
3.)
4.)
Inspect O-rings and the polytetrafluoroethylene (PTFE) extrusion washer.
Reinstall the valve. Tighten the valve in its seat to approximately 30 ft-lb.
Velocity Fuse
There is a brass velocity fuse with a stainless steel spring in the base of each cylinder. The fuse is a
safety feature that activates if a pump failure occurs.
If the pump were to fail,
the
deck
would
lower
much
more rapidly
.
However, a
s soon as the descent speed exceeds
a
preset
threshold
speed, the velocity fuse
closes and
prevents
oil
from
flow
ing.
When the fuse shuts, t
he platform
stop
s
lowering and maintain
s
position
until
hydrualic
pressure is re
e
stablish
ed. This safety feature reduces the
likelihood
of personal
injury or
property
damage
as a result of
pump failure
. To reset the velocity fuse
,
briefly activate
the
pump by
pressing the
"RAISE"
button.