LIFT HYDRAULICS
Fig.
C.0/3
illustrates
the hydraulic working
diagram
of
the
lift
unit.
The
oil
pump (Item
P)
feeds
directly
on transmis-
sion
oil through a screen type
filter
(Item 59), in-
ternally provided
with
a magnetic element which
catches and retains
circulating
metallic
particles
(if any) and delivers
it
to
the
hydraulic
lift
control
valve (Item
D).
The oil
quantity
which is not utiliz-
ed by the
lift
cylinder
drains
into
the hydraulic
lift
body from which
it
flows
back into the transmis-
sion
housing through a suitable
duct
(Item 93).
A
plastic
tube
(Item
33)
connects
the
upper
compartment
of
the transmission housing with
the hydraulic
lift
and serves to equalize the
pressure. The transmission housing, which also
serves as reservoir for the hydraulic lift, contains
17 quarts
(16 litres)
of
oil, 10.6 quarts (10 litres)
of
which can be utilized,
with
tractor standing on
level ground, for hydraulic
lift
operation and for
that
of
auxiliary external ram applications,
if
any
(see page
152) (Fig. C.0/4), illustrates the three
working phases of the hydraulic
lift
and the
operation is described in the legend. The valves
contained in the hydraulic
lift
block and
their
ma-
jor
features are
as
follows:
1.
The double section
pilot
valve (Item
2)
tunc·
tions
as a hydraulic cock. If bottomed on
its
seat
it
prevents the
oil
from draining
out
(lif-
ting phase), and
if
lifted
off
allows
oil
drain-
ing (neutral and lowering phases).
2.
The one-way
cylinder
inlet
valve (Item
5).
Dur-
ing the
lifting
phase the valve opens to let the
delivery
oil
out. In the other phases the valve
is held closed by the pressure
of
the
oil
trap-
ped inside
the
cylinder.
3.
The drain valve (Item
4)
which, when bottom-
ed on
its
seat, keeps the
oil
inside the
cylinder
(neutral or
lifting
phase) and dumps
it
when
lifted
off
its
seat (lowering phase).
4.
The pressure relief valve (Item
1),
set at
2062-2204
PSI
(14217·15203 kPa),
protects
the
hydraulic pump and
oil
lines.
5.
The
cylinder
safety valve (Item
3),
set at
2845·2987
PSI
(19616·20595 kPa)
limits
the
dynamic
stresses
acting
upon
the
mechanical
components
(stresses which
may
occur
when hauling
implements
on
bumpy
roads or ground.)
The
most
important
function
of
the hydraulic cir·
cuit
is, however,
that
performed by the direc·
tiona!
control
valve spool (Item
6)
or
rotating
valve,
which
indirectly
controls
the
closing
of
the
pilot
valve
(SchematicS)
and, directly,
the
open·
ing
of
the drain valve (Schematic
A).
The distribu-
tion
of
the
oil
to
the
cylinder
is the same
for
both
position
and
draft
control
operations. That which
changes is the leverage
quantity
controlling
the
valve spool rotation, the operation
of
which is il-
lustrated in Fig.
C.0/5
and described in the
two
following
paragraphs.
MECHANICS
OF
THE HYDRAULIC LIFT POSI·
TION CONTROL OPERATION
The diagram
(X)
of
Fig. C.0/5 illustrates the inter-
nal and external leverage subassemblies which
is
involved in
position
control operation.
The downward
shifting
of
the selection lever
(Item
B))
for
position
control
operation deter-
mines
the release
of
roller (Item 64) from the ex-
ternal levers (Items
62 and 63) and the upward
rotation
of
the cam (Item 65) which comes in con-
tact
with
the lever (Item 63). The external levers,
active in draft
control
(see diagram
Y)
are
therefore excluded.
When the lever (Item
A)
is moved up in the con·
trol sector, the movements
of
the leverage are
those
indicated by the black arrows in scheme X
and make
the
spool (Item
6)
turn to the
position
of
delivery. As soon as the
piston
moves, the
lever (Item
39), connected
to
the inside arm, acts
upon the rocker arm (Item
66)
in the direction in-
dicated by
the
arrows drawn in
light
lines and
tends
to
bring
the
spool back to neutral.
This
condition,
however,
occurs
only when the
lift
arms reach
the
position
set by the lever (Item
A)
within
the
sector
range.
During the lowering phase the leverage moves in
the
opposite
direction.
In floating,
the
spool
is
permanently kept in
spill
position
and the travel
of
the lever (Item 39), in
this
case, is
not
suffi·
cient
to
bring
it
back
to
neutral.
MECHANICS
OF
THE
DRAFT
CONTROL
OPERATION
In qraft
control,
the
forces applied to the imple·
ment
and
transmitted
through the
top
link
(Item
30, Fig. C.0/5, Diagram
Y)
deform the control spr·
ing
(Item 94).
As these
deformations
are
strictly
dependent
upon
the
position
of
the lever (Item
A)
in the con-
trol
sector,
the
control
valve
will
go
neutral (thus
preventing downward
motions
of
the
implement)
only
when, for a given lever setting, the force
(Item
F)
transmitted
from the
top
link
to
the spr-
ing
is
such
to
impart
to
the latter a correspon-
ding
deformation.
Any further
spring
deformation caused by load
variation
transmitted
through
the top
link, moves
the
valve spool
off
neutral. The valve is thus
automatically
controlled
by the load imparted by
the
implement
to
the
spring through the top
link
so that:
Hydraulics • 153
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