HYDRAULIC CIRCUIT
"LOAD SENSING - SEMI-COMPENSATED"
DISASSEMBLY OF COMPONENTS
MAHYDLS.01
INDEX
INTRODUCTION ......................................................................................................................... 1
HYDRAULIC SYSTEM DIAGRAM............................................................................................... 2
SYSTEM COMPONENTS AND CONNECTIONS........................................................................ 3
DISMANTLING AND SERVICE OF THE COMPONENTS .......................................................... 4
1 - INTRODUCTION
This manual provides the information necessary for a correct and safe way to carry out maintenance works not included in the
INSTRUCTION HANDBOOK FOR OPERATING AND MAINTENANCE; it is addressed to qualified fitters, who know enough about
mechanical components and the functioning of hydraulic and electrical systems for the machine on which it is operating.
The action necessary to implement and enforce the policies related to the Environment and Health and Safety procedures are
left to the responsability of the workshop manager.
This is the symbol used to identify the size of the spanner used for operations described in this handbook. The spanner
type will be advised only if it is different from the standard.
HYDROSTATIC OIL
ESSO HVI 46
Viscosity (ISO 3448) = 46.
Classification to DIN 51524,2 = HLP 46.
If a different brand of oil is used, ensure that is has the caracteristics equal to the specified ESSO products. Should you wish to
change the product brand, the system must be flushed clean of the original oil.
The use of oils with characteristics different to the above ESSO product will bring to the automatic withdrawal of the warranty on all
components of the hydrostatic system.
Check oil level daily.
Replace oil and cartridge filter (86) at the intervals shown in the INSTRUCTION HANDBOOK.
CHECK INSTRUMENTS
It is advisable to use the following pressure gauges (glycerine immersed) and instruments:
- 2 pressure gauges, scale end 600 bar (one of them is already assembled in the vehicle cab)
- 1 pressure gauge, scale end 40 bar.
- 1 R.P.M. counter, scale end 5000 RPM.
- 1 thermometer, scale end 100° C.
- 1 tester : current I = 1,5 A (scale end) / voltage V = 30 V (scale end).
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2 - HYDRAULIC SYSTEM DIAGRAM
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2 - HYDRAULIC SYSTEM DIAGRAM
1 Suction line filter
2 Return line filter
3 Pump
4 Diesel engine
12 Volume recovery valve
17 Power steering
18 Steering directional control valve
19 Steering rams
22 Pressure gauge
23 Main directional control valve
24 Telescoping ram lock valve
25 Lifting ram
27 Telescoping ram
30 Compensation valve
31 Compensation ram
32 Carriage ram lock valve
33 Carriage ram
36 Front snap couplings Ø 1/2"
42 Snap coupling Ø 1/2"
66 Movements locking solenoid valve
67 Tac-lock ram
68 Lifting ram lock valve
90 Pressure check plug
94 Accumulator
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3 - SYSTEM COMPONENTS AND CONNECTIONS
INDEX
MAIN COMPONENTS ................................................................................................................................................................ 2
POWER SUPPLY OF AN HYDRAULIC SYSTEM DIAGRAM ............................................................................................................ 3
LS PUMP (Load Sensing) and "DFR" (3)..................................................................................................................................... 4
THE DISTRIBUTOR (23)............................................................................................................................................................ 6
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3 - SYSTEM COMPONENTS AND CONNECTIONS
MAIN COMPONENTS
WARNING!!! This is only an example of a hydraulic system. It is intended purely as an illustration and for didactic
purposes. When carrying out a maintenance operation, ALWAYS refer to the hydraulic system diagram present in the
machine's "Operator's Manual".
(3) THE LS PUMP (Load Sensing) and the "DFR
(23) THE DISTRIBUTOR
3-2
3 - SYSTEM COMPONENTS AND CONNECTIONS
POWER SUPPLY OF AN HYDRAULIC SYSTEM DIAGRAM
WARNING!!! This is just an extract from a generic
hydraulic system diagram. It is intended purely as an
illustration and for didactic purposes. When carrying out
maintenance operations ALWAYS refer to the hydraulic
system diagram present in the machine's "Operator's
manual".
1 Suction line filter
2 Return line filter
3 Pump
4 Diesel engine
23) Main directional control valve
3-3
3 - SYSTEM COMPONENTS AND CONNECTIONS
LS PUMP (Load Sensing) and "DFR" (3)
Pump diagram
S) Suction from tank L1) Pump stopper
L) Casing drainage to tank DFR) DFR apparatus
X) Piloting signal of circuit VLS) Stand-by pressure register
B) Supply to circuit VP) Pump maximum pressure register
L) Tank drainage 90) Pressure testing point
Functioning of the pump
The LS pump is a variable piston pump, so, has variable delivery.
Variable delivery is obtained using a system of axle pistons which, turning in a drum, slide on a plate (flat) that can be inclined at
various angles.
Modifying the angle of the plate changes the course of the pistons, producing a different delivery.
The main characteristic of this pump is that it has a variable delivery that depends on the demands of the system, always following the
formula:
P = pxQ
where:
P = Power
p = Pressure
Q = Flow
In other words, the pump works at constant power, reducing the delivery when the circuit demands a higher pressure.
When there is no demand for oil, the pump positions itself at its minimum delivery and, the circuit pressure, remains on stand-by with
a value that, in this application, is about 22-24 bar (stand-by pressure).
When the operator acts on the machine's hydraulic controls, a pressure signal reaches the pump from the distributors via the piloting
line and the pump increases its delivery.
The piloting line gives a signal of retro-action to the pump and, the pump regulates its delivery depending on the pressure demands at
that moment.
The regulating apparatus of the pump is the DFR.
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3 - SYSTEM COMPONENTS AND CONNECTIONS
On the DFR apparatus there are two regulators:
Stand-by pressure regulator (VLS)
The stand-by pressure is the pressure that permanently pressurises the circuit, when hydraulic manoeuvres are not being carried
out. The stand-by pressure retroactively returns to the pump non appena as soon as the operator decides to carry out a hydraulic
manoeuvre.
Pump maximum pressure regulator (VP)
When the circuit pressure reaches the input value, this mechanism causes the pump plate to turn towards its minimum angle,
progressively reducing the capacity.
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3 - SYSTEM COMPONENTS AND CONNECTIONS
THE DISTRIBUTOR (23)
Main components
S1) Mechanically controlled sections.
S2) Logic element.
S3) Servo controlled sections.
A) Mechanically controlled cursor.
B) Compensated flow limiting valve.
C) Compensator.
D) Maximum pressure valve.
E) Electro-valve for manoeuvres release.
F) Hydrostat.
G) Servo controls pressure reducer valve.
H) Compensator.
I) Electro-hydraulically controlled cursor.
L) Calibrated hole (1 mm).
M) Non return valve.
N) Fall preventing valve.
O) Non return valve on the "Load sensing" circuit
(two spheres inside each sensor).
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3 - SYSTEM COMPONENTS AND CONNECTIONS
3-7
4 - DISMANTLING AND SERVICE OF THE COMPONENTS
LOAD SENSING PUMP SERVICE
NB!!! Service of the pump is considerably difficult and must be carried out by competent technicians. Therefore it will
not be dealt with in this manual.
"DFR" REGULATOR SERVICE
WARNING!!! When carrying out the following operations on the machine, a certain amount of hydraulic oil could leak
from the system. Prepare a suitable collection system to avoid polluting the earth and unnecessary waste.
NB!!! These operations can be carried out without removing the DFR from the pump and without altering the settings.
Service of regulation system for stand-by pressure
(1) Slider (4) Washer
(2) Spring guiding pin (5) Regulation group
(3) Spring
- Unscrew the stand-by pressure regulation group (5).
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
- Remove the stand-by pressure regulation group (5); with the aid of a magnet extract in order, the spring guide (2) and the
internal slider (1).
Service of the pump maximum pressure regulation system
(1) Slider (4) Spring
(2) Spring guide (5) Washer
(3) Spring (6) Regulation group
- Unscrew the regulation group (6).
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
- Remove the regulation group (6); with the aid of a magnet extract in order, the spring guide (2) and the internal slider (1).
Removal of the DFR from the pump
- Disconnect the pilot hose (A) from the DFR, and the four
securing screws (B) of the pump.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
DISTRIBUTOR SERVICE
SEPARATION OF SECTIONS FROM THE LOGIC ELEMENT SECTIONS (S2)
1) On the side of mechanically controlled sections, uncrew the four fastening nuts of the head, then separate the latter from the
sections.
2) With the help of a screwdriver, extract completely from the supports the mechanically controlled sections, thus separating them
from the logic element.
3) Unscrew the four fastening nuts on the servo-controls side of the head; with the help of a screwdriver, extract this completely.
4-4
4 - DISMANTLING AND SERVICE OF THE COMPONENTS
4) Finally, separate the two servo controlled sections from the logic element.
SERVO CONTROLLED SECTION SERVICE
5) Unscrew the four screws fastening the servo control to the corresponding section; remove the components.
6) Remove the entire servo controlled component; extract the bush/valve group.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
7) Extract the valve (2) from the bush (1).
8) With the help of a screwdriver, extract the two valves of the servo control.
9) Check the state of the o-ring seals.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
10) Unscrew the two screws fastening the block to the main section.
11) Extract the block, unscrew the two screws fastening the cursor manual control to the main section.
12) Extract the cursor manual control.
4-7
4 - DISMANTLING AND SERVICE OF THE COMPONENTS
13) Remove the indicated gasket (1).
14) On the centering spring side, extract completely the bar (3) and the gasket (2).
15) If you wish to disassemble the components on the bar, it
is recommended to measure the calibration with a gauge
while the grindstone is in compression (as indicated in
the picture) before starting the operation.
4-8
4 - DISMANTLING AND SERVICE OF THE COMPONENTS
16) Remove the fall preventing valve valve, check the state of the o-rings, the spring and the cursor seating.
MECHANICALLY CONTROLLED SECTION SERVICE
1) Extract the rubber protection.
2) Unscrew the levers of the cursor mechanic control.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
3) Rotate to one side (see picture) the section and procede to the removal of the indicated screws.
4) On the opposite side, unscrew the fastening screws of the centering spring cap; remove the cap.
5) Extract the cursor from its seating. The two sections are now separated.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
6) If you wish to disassemble and replace the spring on the cursor, make sure to measure the compression height of the screw (as
indicated in the picture) before proceeding.
LOGIC ELEMENT SERVICE
1) Unscrew the 8 screws fastening the aluminium block and extract this from its seating on the main block.
2) Extract the two compensators from their seatings by pulling them to the outside.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
3) If you wish to disassemble the components on the bar, before starting this operation it is recommended to measure with a gauge
the calibration of the cursor end stop and the compression height of the spring (picture b).
4) Check the o-rings.
5) Unscrew the fastening nut and extract the solenoid.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
6) Unscrew and remove the electro-valve.
7) Using a scredriver, remove the compensated flow limiting valve.
a) Valve body c) Bar
b) Spring d) Seeger
4 - 13
4 - DISMANTLING AND SERVICE OF THE COMPONENTS
8) Remove the pressure reducing valve for the servo controls; check the o-rings.
9) Remove the hydrostat with its spring.
10) With the help of a wrench, extract the bar.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
a) Hydrostat b) Spring
c) Bar
11) Remove the top and then the setscrew.
12) Check that the 1 mm hole on the setscrew is free from
any debris.
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4 - DISMANTLING AND SERVICE OF THE COMPONENTS
13) Unscrew and remove from its seating the maximum pressure valve.
14) Also remove the basket left inside the hole. (a) electro-valve body - (b) gasket.
15) Remove the top and then, with the help of a screwdriver, uncrew the non return valve.
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