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Section D
35 - 4
Basic System Operation
Component Key:
A
Right hand joystick
B
Left hand joystick
D
Pilot supply valve
E
Supply valve solenoid
F
Oil filter
G
Accumulator
H
Right hand pilot control valve
J
Left hand pilot control valve
K
Seat mounted micro switch
L
Joystick mounted 'mode switch'
M
Loader valve block
N
Excavator valve block
P
Machine hydraulic tank
Q
Pressure relief valve
R
Fuse
S
Solenoid manual override control knob
S1a
Excavator Pilot port - Slew ram spool
S1b
Excavator Pilot port - Slew ram spool
S2a
Excavator Pilot port - Boom ram spool
S2b
Excavator Pilot port - Boom ram spool
S3a
Excavator Pilot port - Dipper ram spool
S3b
Excavator Pilot port - Dipper ram spool
S4a
Excavator Pilot port - Bucket ram spool
S4b
Excavator Pilot port - Bucket ram spool
T
Tank
Note that the diagram opposite shows the servo hoses
connected to give the SAE + (JCB +) control pattern. For
ISO + control pattern some servo hoses are connected
differently at the excavator valve, as shown at Z.
Electrical Operation
A solenoid actuated valve is incorporated in the pilot supply
valve block D. The solenoid is controlled either by micro
switch K or 'mode switch' L.
When the operator seat is revolved to face the rear of the
machine switch K is closed. This energises solenoid E and
oil at pilot pressure is diverted to the 2 pilot control valves H
and J, thus enabling the system. Solenoid E also
incorporates a manual override facility (S). This enables the
backhoe to be operated in an emergency situation, in the
event of solenoid or electrical failure for example.
In some circumstances the operator may require actuation
of the backhoe with the seat in the forward position (when
un-sticking from boggy ground for example). This is
achieved by means of joystick mounted mode switch L. The
switch energises solenoid E and the system is enabled.
The left hand joystick houses a horn switch. On some
machines the joysticks also incorporate switches for control
of a hydraulic quickhitch and changeover from auxilary
(typically jaw bucket) to extending dipper operation.
9803/3280
Precision Control (Servo)
Purchased from www.WorkshopManuals.co.uk
Controls
Hydraulic Operation
Oil at system pressure flows to the pilot supply valve D via a
hose connected at the loader valve M. An integral pressure
relief valve Q maintains the oil at 'pilot' pressure.
When the operator actuates the system by revolving the
seat to face the rear, or by operating the mode switch,
solenoid E is energised and moves the pilot supply valve
spool. Oil flows to the pilot control valves H and J.
Each pilot control valve contains four spool valve 'capsules',
numbered 1 to 4 on each valve. The valves are operated by
moving the associated joystick. With the joystick in the
neutral position all the valves vent oil from the excavator
valve pilot ports S1-S4 to tank.
Example Operation:
When the operator moves the right hand joystick forward
the mechanical linkage connected to pilot valve H pushes
spool 1 down. Oil at pilot pressure is diverted to port S3b.
in the excavator valve N. This causes the dipper spool to
move and operate the dipper ram. As the dipper spool
moves, oil is vented from port S3a via spool 3 and port T in
control valve H.
The valve 'capsules' feature proportional control. This
enables backhoe precision control. Each valve capsule
modulates oil pressure supplied to the associated excavator
valve pilot line in proportion to the joystick position. The
further the joystick is moved the greater the pilot pressure
and the further the associated excavator valve spool moves.
Accumulator G maintains hydraulic pressure for several
operations of the excavator spools with the engine stopped.
This allows venting of pressure from the backhoe hydraulic
rams, or lowering of a load in the event of engine failure.
Section D
35 - 4
Issue 1
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