Load sensing control 2M4-12.pdf

Electric Drives
and Controls Hydraulics
Linear Motion and
Assembly Technologies Pneumatics Service
Project manual
Mobile hydraulics
Load sensing control 2M4-12
Trainer's manual
RE 09970/03.11
Replaces: 05.08

1
RE 09970/03.11 I Foreword Bosch Rexroth AG
Foreword
The present project manual for the area mobile hydraulics serves as accompanying and
work book for the knowledge transfer by means of project works. Projects are described
that are especially based on practical examples from the mobile control technology. The
trainees are expected to have basic hydraulic knowledge.
It must generally be noted that the project results documented in this manual may slightly
vary depending on the relevant circumstances.
Project / trainer information
For the projects with mobile hydraulics, the device set has been extended. For explana-
tions on the practice stand, please refer to the corresponding operating instructions.
Before the projects are carried out, the hydraulic basics should be discussed and intro-
ductory practice described must have been completed.
We recommend carrying out the projects in the specified order starting with project 01.
The description of a project practice comprises information for trainers as well as project/
trainer information for the completion of the relevant project.
This information is only contained in the trainer manual.

2 Foreword I RE 09970/03.11
Bosch Rexroth AG
Notes

3
RE 09970/03.11 I Introduction Bosch Rexroth AG
Introduction
History of mobile hydraulics
Since the 1960s, construction machines have increasingly been operated with hydraulics.
Before, mainly fully mechanical rope machines were used.
With these machines, the force was transmitted by means of gears and couplings.
The machine operator must operate the mechanical couplings with large levers.
Operation was a real feat of strength.
As compared to today's machines, the working speed were relatively slow.
The efficiency of excavator applications on construction sites was not perfect.
A rope excavator with gripper can hardly penetrate solid ground and often only scratches
at the surface.
Thanks to the hydraulics, the force transmission is more flexible and easier than with pure
mechanics.
The large, heavy gears and couplings as well as the rope drums could be omitted.
As then, the hydraulics often did not have today's tried and tested components, there
were many problems to lose for the piping and hose material for the high pressures had to
be developed and improved first. The same was true for pumps and control blocks.
The working movements of the first hydraulic excavators were much slower and more
jerky than with today's hydraulic excavators.
Fig. 0-1: Rope excavator 1928 in operation

4 Introduction I RE 09970/03.11
Bosch Rexroth AG
In the beginning, the hydraulic control blocks were arranged under the operator who oper-
ated the directional valve spools by means of mechanical levers.
The introduction of the hydraulic remote control was another step; it simplified the opera-
tion and made the arrangement of the control blocks in the machine more flexible. Now,
the control block could be mounted in places where it was e.g. most favorable for the
piping.
The machines became faster and faster and increasingly powerful.
Fig. 0-2: Hydraulic excavator today
Adjustment boom
Hydraulic
pumps
Diesel motor
Hydraulic control block
Slew drive
Arm
Bucket
Operating elements

5
With the increased working speeds, the jerky motion sequence had more and more nega-
tive effects. The advancement focused on the optimization of the controls regarding the
best and jerk-free controllability of the working movements possible
(load sensitivity).
The previously used throttle control was amended by load sensing systems in the 1980s.
Load sensing reduces the power loss and simplifies the operation as the control is load
pressure-independent. Apart from that, the multi-circuit systems with several pumps nec-
essary in the throttle control could be replaced by one-circuit systems with one pump.
Another development is the LUDV system, in which the flow is load pressure-independent
of all operated actuators (LUDV = abbreviation of the German term for load pressure
independent flow distribution).
The special advantage of this system is that no actuator stops when all operated actua-
tors require more oil than can be delivered by the pump. In this case, the LUDV system
reduces the actuator velocities proportionally according to the pump delivery volume.
In the future, also electronic systems will be used by means of which the actuator veloci-
ties and pumps will be controlled.
Fig. 0-3: Harvester in forestry operation

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Notes

7
Knowledge transfer by means of project works
By means of the mobile hydraulic project manuals, the necessary expert knowledge regarding
the hydraulic control technology can be transferred in practice-oriented applications.
Logically set-up project works are to help the trainee:
• To understand physical principles like pressure differential, opening cross-section and
flow,
To read specific switching symbols,
•
To identify the function of the throttle control,
•
To understand the connection between control and velocity,
•
To get to know the function of the throttle control in parallel operation,
•
To work out the function and application of the hydraulic pilot control,
•
To carry out measurements of specific values.
•
The project tasks and project works described in the mobile hydraulic project manuals
provide the trainers and trainees with information and instruments for satisfying the re-
quirements on the knowledge transfer regarding the hydraulic expert knowledge.
Due to the preparedness and ability to solve tasks and problems on the basis of technical
knowledge and skills in a target-oriented, appropriate, method-guided and independent
way and to evaluate the result, the trainees develop their technical competence.
Teaching
contents
Technical
competence

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As mentioned above, the trainee is to work off the project task and/or the project order in
6 steps.
1. Information
On the basis of the project definition, the trainee is to get a clear idea of the complete
solution including the necessary details. This is possible by the systematic analysis of the
project documents and queries, if necessary.
Possible auxiliary questions: a) What is to be done?
b) Have I understood the task completely?
c)
Which hydraulic component / system is to be
worked out?
2. Planning
Planning means theoretical preparation and anticipation of a concrete execution. In detail,
planning requires the competence for processing the project order and for organizing the
project processing steps.
Possible auxiliary questions: a) How to proceed?
b) Which knowledge is necessary?
c) Which aids are available?
d) Are there comparable applications in my company?
3. Decision-making
After the planning phase, the trainee makes the decision regarding the determination of
the aids, e.g. which data sheets are necessary for processing the project task. He also
makes the decision regarding the sequence and the dependencies of the individual proj-
ect steps. It must also be decided whether the project task can be completed more easily
in a team.
Possible auxiliary questions: a) Which hydraulic and electrical components are used?
b) How do you recognize the up-to-dateness of the
data sheets?
c) Have I used all possible sources of information?
d) Do I have the prescribed safety instructions?
Professional
competence
of action

9
4. Execution
The order will be executed according to the work instructions in Order execution chap-
ter complying with the safety instructions. After a careful preparation phase, the trainee
should execute the project order as independently as possible. After preparation of the
written solution, it should be verified and/or asked whether the correct solution has been
chosen.
Possible auxiliary question: a) Have I chosen the correct order?
5. Checks
The trainer checks the intermediate results already during the execution phase. Some-
times, the result can be compared to manufacturer documents. In measurement practice it
has to be checked whether the measurement results are realistic.
The documentation is also to be finally corrected, improved, finished and completed. This
includes the preparation of the final report. Upon completion, there is a final check by the
trainer.
Possible auxiliary questions: a) Has the control been mounted professionally?
b) Has the project target been achieved?
c) Which documentation is necessary?
d)
Is the result complete and documented in an or-
dered form?
6. Evaluation
In the final evaluation face, the comparison of project order documents, assembled control
and measurement and control results is to be used as basis for an external or own evalua-
tion.
Possible errors and error causes are to be analyzed and the possibilities for avoiding
future errors are to be discussed.
The trainees are to learn to assess their strengths and weaknesses and to develop objec-
tive quality standards for their actions which will finally lead to personal competence. The
evaluation can be completed by a technical discussion, also with a customer discussion, if
applicable.

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General instructions:
For didactic reasons, the present manual only talks of trainees and trainers. It is express-
ly stated that it also refers to all other parties involved in the training and further develop-
ment: The female trainees and trainers, the female and male teachers, project managers,
etc.
In this manual, we do not provide any information on procedural knowledge (explanatory
knowledge). It is the knowledge on which measures, procedures or processes are nec-
essary to achieve a certain result. In this case how the learning target can be achieved.
The present manual is to be understood as tool for transferring the required core and
technical qualifications that are to be transferred in the industrial metal professions in
an integrated form according to the regulation on the professional training considering
independent planning, executing and controlling.
As recurring individual symbols, the listed pictograms are to transfer information as simpli-
fied graphical presentation in a language-independent form and as fast as possible.
Procedural
knowledge
Pictogram
Notes

11
Safety aspects
So that the possible dangers of machines and systems are recognized, safety regulations,
product information and operating instructions must be observed.
The present mobile hydraulic project manual contains information referring to the risk of
personal injury or damage to property.
The measures described foravoiding dangers must be adhered to.
The signal words/symbols have the following meaning:
Warning sign (warning triangle)
• → Draws attention to the hazard
Signal word
• → Identifies the degree of hazard
Type of risk
• → Specifies the type or source of the hazard
Consequences
• → Describes the consequences of non-compliance
Precautions
• → Specifies how the hazard can be prevented
The following table summarizes the application of the most important pictograms and
signal words.
Important:
The electrohydraulic components and systems described in the project manual are tech-
nical equipment and not designed for private use.
The intended use also includes having read and understood the subsequently listed
safety regulations, product information and operating instructions.
Signal
word
Application
Danger
Indicates an imminently hazardous situation which will certainly result in
serious injuries or even death if not avoided.
Warning
Indicates a potentially hazardous situation which, if not avoided, could
result in death or serious injury.
Caution
Indicates a potentially dangerous situation which can could result in
moderate or minor injuries or damage to property if not avoided.
Non-compliance with this information may result in deterioration in the
operating procedure.

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Assembly, commissioning and operation, disassembly, service and maintenance require
basic mechanical and electrohydraulic knowledge as well as knowledge of the appropri-
ate technical terms. In order to guarantee operational safety, these activities may only be
carried out by a corresponding expert or an instructed person under the direction and
supervision of an expert.
Experts are those who can recognize potential hazards and apply the appropriate safety
measures due to their professional training, knowledge and experience, as well as their
understanding of the relevant conditions pertaining to the work to be undertaken. An
expert must observe the relevant specific professional rules.
This means that the trainer must finally inform the trainee about possible dangers and the
related prevention of dangers.
In case of improper works at hydraulic components and systems, there is a risk
of injury as well as a safety risk when operating the system, including danger
to life!
In case of damage resulting from the improper use and from unauthorized interventions
not intended in the mobile hydraulics project manual, any liability for defects and any liabil-
ity claim vis-à-vis Bosch Rexroth AG will be forfeited.
If the projects 01 to 11 described in the mobile hydraulics project manual are carried out
at practice stands and with electrohydraulic components not supplied by Bosch Rexroth,
i.e. competitor makes, any liability for defects and any liability claim vis-à-vis Bosch
Rexroth AG will be forfeited in this case, as well.
When using competitive products, the safety instructions prescribed by the
manufacturer apply, whereas it has to be ensured that the components and sys-
tems comply with the currently valid and relevant EU directives.
The commissioning is therefore prohibited until it was confirmed that the hy-
draulic components and systems that are to be used comply with the provisions
of all relevant EU directives.
Important:
The necessary safety provisions, product information* and operating instructions must be
handed over to and/or be accessible to the trainee in the latest version.
In the mobile hydraulics project manual, no explicit reference is made in the project prac-
tice 01 to 11 to the correct handling of hydraulic fluids. For corresponding information,
please refer to the safety data sheet.
*
Bosch Rexroth product information only applies to hydraulic products that are oper-
ated with hydraulic fluid on mineral oil basis unless other hydraulic fluids are explicitly
admitted in the operating instructions.
Qualification
of personnel
Warning
Liability
Warning

1
RE 09970/03.11 I Basics of mobile hydraulics Bosch Rexroth AG
Basics of mobile hydraulics
Mobile hydraulics are used in mobile machines.
In most cases, these are earth-moving machines like e.g. excavators, wheel loaders and
caterpillars.
Another field of application is agricultural and forestry machinery like e.g. tractors and
wood harvester machinery.
Cranes and forklifts are part of the conveyance field of application.
In mobile machines, the force is transmitted from the diesel motor to the working equip-
ment by means of hydraulic fluid. The processes are controlled by hydraulic control tech-
nology.
In mobile hydraulics, the two basic principles of hydraulic are used:
The principle of the closed circuit with hydraulic pump and hydraulic motor is mainly
1)
used for traction drives, winches and slew drives.
In the closed circuit, the return oil from the actuator is directly fed back into the pump.
The velocity is checked by adjusting the pump and the motor.
Parallel operation of several actuators and single-rod cylinders is not possible.
Abtriebsdrehzahl
n = variabel
Volumenstrom
q = variabel
Hilfspumpe zum
Leckageausgleich
Auxiliary pump for leak-
age compensation
Flow
q = variable
Output speed
n = variable
Cooler
Fig. 0-4: Closed hydraulic circuit

2 Basics of mobile hydraulics I RE 09970/03.11
Bosch Rexroth AG
2. The open circuit with hydraulic pump, cylinders and hydraulic motors is used for appli-
cations with working equipment and several simultaneously operated actuators.
In the open circuit, the return oil from the actuators is led into the tank and is then
sucked in again by the pump.
For controlling the actuators, valves are necessary.
With the circuit diagram shown, there is high power loss in the unoperated condition
of the directional valves as the entire pump delivery volume is delivered to the tank at
maximum pressure.
Volumenstrom
q = konstant
Flow
q = constant
Fig. 0-5: Open hydraulic circuit

3
The machines are controlled by a machine operator. This operator controls the move-
ments having the working equipment or the load in view. Automatic operation as in indus-
trial systems is normally not possible.
A control that can easily be controlled and easily be operated is important.
With mobile machines, low component weight and good efficiency are important.
Bad efficiency means high losses and makes itself felt in high fuel consumption rates.
In 11 projects, this manual deals with the control technology in the open circuit with the
load sensing control.
Fig. 0-6: Crawler excavator

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Load sensing (LS), load pressure signal
Load sensing systems (LS systems) have been developed in order to eliminate the de-
pendency of the throttle control on the load pressure and to reduce the high power loss.
This resulted in more efficient systems that can be operated more easily. The efficiency
could be achieved by means of pumps controlled by the load pressure, which are always
adjusted to the relevant load conditions.
Due to the load pressure compensation, the machine operation could be simplified.
There are numerous applications for load sensing systems like e.g. construction machinery,
forestry machinery, drilling equipment, cranes, stackers and stationary applications.
Load sensing is the recording (measurement) of the load by the load pressure. This load
pressure signal is used for controlling the pump and pressure compensators.
The load pressure signal is generally also referred to as LS signal.
For the correction functioning, it is important to always record and forward the highest
load pressure signal.
For that purpose, the pressure is recorded by the relevant working port by means of bores
in the directional valve spools and forwarded to the pump controller via shuttle valves.
The shuttle valves guarantee that in parallel operation, always the highest load pressure is
forwarded to the pump controller.
Fig. 0-7: Displacement-controlled pump with load pressure signal (LS) for individual actuator operation (load 100 bar)
pP 110 bar
pL2 100 bar
pL1 10 bar
pLS = pL2
100 bar
Control spring = 10 bar
ΔpLS = pP – pLS
= 100 bar
Shuttle valve
pP = 110 bar
Load pressure
signal

5
The pump controller is a so-called displacement controller and controls the pressure differ-
ential ΔpLS.
The pump controller has been designed so that the pump pressure pP always exceeds the
load sensing signal p LS by a certain value (e.g. 10 bar).
Here, you also talk of ΔpLS = pP – pLS.
With the pressure differential ΔpLS, the oil is delivered through the resistances of lines and
control block.
The pump controller always keeps the pressure differential ΔpLS constant, i.e. changes in
the load pressure also result in changes in the pump pressure.
This is to be clarified by an example:
The load pressure of a cylinder = pLS = 100 bar, the pressure differential ΔpLS = 10 bar.
The pump pressure pP = pLS + ΔpLS = 100 + 10 = 110 bar.
This means in practice that if possible, the pump pressure should only be 10 bar higher
than the highest load pressure in the system.
The force of the control spring in the pump controller determines the pressure differential
ΔpLS. The spring force can be set by means of a set screw. The amount of the pressure
differential ΔpLS depends on the resistances in the lines and control blocks and may range
between 10 and 22 bar.
Energy balance
In order to show the energy differences, 3 systems are compared:
Fixed displacement pump with throttle (constant delivery system)
A
Pressure-controlled pump with throttle (constant pressure system)
B
Displacement-controlled pump with throttle (load sensing system)
C
A Fixed displacement pump with throttle (constant delivery system)
A fixed displacement pump always delivers the same flow into the system. The pressure is
determined by the loads and resistances. The maximum system pressure is determined by
the pressure relief valve. The delivery rate is 100 l/min, the max. system pressure is limited
to 200 bar. The cylinder is loaded with 50 bar and the throttle is set so that 25 l/min flow.
The delivery volume not flowing to the cylinder is discharged to the tank via the pressure
relief valve.
The power calculation results in:
Drive power: PDrive = 200 bar • 100 l/min / 600 = 33 kW
Effective power: PEffective = 50 bar • 25 l/min / 600 = 2 kW
Power loss DB: PLoss 1 = 200 bar • 75 l/min / 600 = 25 kW
Power loss throttle: PLoss 2 = (200 bar – 50 bar) • 25 l/min / 600 = 6 kW
Of 33 kW drive power, only 2 kW are utilized for the working movement and 31 kW are
converted into heat. The pump efficiencies have not been considered.

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B Pressure-controlled pump with throttle (constant pressure system)
A pressure-controlled pump only delivers the flow into the system that is necessary in
order to maintain the set pressure.
The pressure is determined by the loads and resistances. The maximum system pressure
is determined by the pressure controller. The delivery rate can be 0 - 100 l/min, the max.
system pressure is set to 200 bar. The cylinder is loaded with 50 bar and the throttle is
set so that 25 l/min flow.
The pump delivery volume is limited to a rate which also flows to the cylinder.
The calculation of the power for the specified conditions results in:
Drive power: PDrive = 200 bar • 25 l/min / 600 = 8 kW
Effective power: PEffective = 50 bar • 25 l/min / 600 = 2 kW
Power loss throttle: PLoss 2 = (200 bar – 50 bar) • 25 l/min / 600 = 6 kW
Of 8 kW drive power, 2 kW are utilized for the working movement and only 6 kW are
converted into heat. The pump efficiencies have not been considered.
A considerable improvement as compared to the fixed displacement pump.
C Displacement-controlled pump with throttle (load sensing system)
A displacement-controlled pump only delivers the flow into the system that is necessary in
order to maintain the set pressure differential (ΔpLS).
The pressure differential is determined by the control spring.
The system pressure is always 10 bar higher than the load pressure.
The maximum system pressure is limited by a pressure relief valve or an additional pres-
sure controller.
The delivery rate can be 0 - 100 l/min, the pressure differential is set to 10 bar. The cylin-
der is loaded with 50 bar and the throttle is set so that 25 l/min flow.
The pump delivery volume is limited to a rate which also flows to the cylinder.
The calculation of the power for the specified conditions results in:
Drive power: PDrive = (50 bar + 10 bar) • 25 l/min / 600 = 2.5 kW
Effective power: PEffective = 50 bar • 25 l/min / 600 = 2.1 kW
Power loss throttle: PLoss 2 = (60 bar – 50 bar) • 25 l/min / 600 = 0.4 kW
Of 2.5 kW drive power, 2.1 kW are utilized for the working movement and only 0.4 kW
are converted into heat. The pump efficiencies have not been considered.
Another considerable improvement as compared to the constant pressure system.

7
Principle of the load sensing system
In order to understand the hydraulic control technology, a certain basic knowledge is nec-
essary.
The flow through a directional valve and thus the actuator velocity depend on two factors.
The opening cross-section and the pressure differential across this cross-section.
The larger the cross-section (A) and the higher the pressure differential (Δp), the higher is
the flow (q). This is expressed by the equation qV = aD • A• √2/r • √Δp.
The factor f is a flow and viscosity coefficient by means of which the properties of oil are
taken into consideration.
A clear example is to clarify the connection between cross-section, pressure differential
and flow.
A Constant pressure system
Fig. 0-8: Pressure differential and flow in the constant pressure system
Pressure
controller
Control spring = 100 bar
Load 2 = 30 bar
Load 1 = 30 bar
Load 0 = 10 bar
d = 5 mm
psys pL
psys – pL = Δp → q
Load 0 100 – 10 = 90 bar
127 l/min
Load 1 100 – 40 = 60 bar
103 l/min
Load 2 100 – 70 = 30 bar 73 l/min
The valve opening corresponds to a bore d = 5 mm, the system pressure is 100 bar, the
load on the cylinder changes with the charging and thus the load pressure.
Using the formula qV = aD • A• √2/r • √Δp, the flow in l/min can be calculated
(A = d2 • π/4). The exact calculation depends on more factors and conditions which are
not to be addressed here in more detail. With hydraulic valves, the flow values are mea-
sured as calculations are difficult due to the flow conditions and the geometry in the hous-
ing.
It can be seen that with increasing load, the pressure differential Δp and thus also the flow
increasingly decrease. This means in practice that with identical valve opening, the cylin-
der moves faster without load than with load.

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B Load sensing system
Using the load sensing system, the pressure differential Δp at the throttling point is kept
constant, at e.g. 10 bar. For that purpose, the load pressure is recorded and forwarded to
the pump's displacement controller.
Together with the control spring, the load pressure acts on the actuating piston, the pump
pressure on the same actuating cylinder surface. Together with the control spring, the
load pressure results in an increase in the delivery volume (→ qmax.).
If the pump pressure pP exceeds the load pressure together with the control spring, this
results in a decrease in the delivery volume (→ qmin.). The pressure in front of the throttle
is therefore always 10 bar higher than the load pressure. The spring force of the control
spring determines the pressure differential Δp at the throttling point.
Fig. 0-9: Pressure differential and flow in the load sensing system
d = 5 mm
psys – pL = Δp → q
Load 0 20 – 10 = 10 bar 42 l/min
Load 1 50 – 40 = 10 bar 42 l/min
Load 2 80 – 70 = 10 bar 42 l/min
Load 2 = 30 bar
Load 1 = 30 bar
Load 0 = 10 bar
LS signal
(load pressure)
Displacement
controller
pp pL
The valve opening corresponds to a bore d = 5 mm, the displacement controller is set to
a pressure differential = 10 bar, the load on the cylinder changes with the charging and
thus the load pressure.
Using the formula qV = aD • A• √2/r • √Δp, the flow in l/min can be calculated
(A = d2 • π/4).
With increasing load, the pressure differential Δp remains constant at 10 bar and thus,
the flow is constant, as well. This means in practice that with identical valve opening, the
cylinder moves as fast without load as with load. This behavior is also referred to as load
pressure compensation.

9
Pressure compensators
In mobile hydraulic applications, you often carry out two movements simultaneously.
The loads of the relevant actuators are mostly different, i.e. the load pressures are differ-
ent, as well.
The pressure pP always exceeds the load pressure of the actuator with the highest load by
the pressure differential ΔpLS.
In this case, the pressure differential Δp1 of the actuator with the lower load pressure is
higher.
Fig. 0-11: Table
Fig. 0-10: Pressure differential and flow in the load sensing system with 2 actuators (without pressure compensators)
pL1 = 20 bar
Z1 = 20 bar
Z2 = 20 → 100 bar
Shuttle valve
d = 5 mm A1 = A2 = 19.64 mm2
Δp2 = ΔpLS = pP – pL2
Δp1 = pP – pL1
Δp2 = ΔpL2
pLS = pL2
20 → 100 bar
Load pressure
signal line
(LS signal)
pP2
30 → 110 bar
pL2
20 → 100 bar
pp pL1 pL2 Δp1 Δp2 q1 q2
30 20 20 10 10 42 42
60 20 50 40 10 84 42
85 20 75 65 10 103 42
110 20 100 90 10 127 42

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The valve openings correspond to a bore d = 5 mm, the displacement controller is set to
a pressure differential Δp = 10 bar, the load pressure of cylinder 2 is changed with the
charging from 20 to 100 bar. The loading of cylinder 1 remains constant with 20 bar.
It must be noted that the flow qV1 strongly increases if the load pressure p2 increases, while
the flow qV2 remains constant due to the load pressure compensation.
In the operation of the machine, this behavior is very annoying.
For a perfect behavior, it is therefore necessary to individually compensate the load pres-
sures for every actuator.
The following graphic shows a system with individual pressure compensators.
The individual load pressure compensation is effected by means of pressure compensa-
tors for every actuator.
By means of pressure compensators, the pressure differential ΔpV at the relevant valve
openings is kept constant.
The pressure compensator comprises a symmetric spool (1) that loaded on the area AK
(2) with the pressure in front of the valve opening and on the other area AK (3) with the
load pressure pL and a control spring (4).
The pressure compensator is opened by the load pressure pL and a control spring (4).
The pressure in front of the valve opening pV closes the pressure compensator.
The control spring (4) corresponds e.g. to 10 bar and the load pressure pL = 20 bar; thus,
the pressure compensator is opened with 30 bar.
The pressure pP = 100 bar is available up to the directional valve due to the opened pres-
sure compensator.
Fig. 0-12: Pressure compensator
pL
AK (2)
Spool (1)
pL
pV
pP
pV
pP
Control spring (4)
AK (3)
pP

11
The pressure in front of the valve opening, however, acts on the spool area (2) and closes the
pressure compensator if 30 bar have been reached. The opening grooves (5) of the pressure
compensator (DW) throttle the oil flow and now, a pressure differential ΔpDW results.
With a pressure differential ΔpDW = 70 bar, 100 bar – 70 bar = 30 are available in front of the
valve opening and the pressure compensator will stop closing as the forces at the spool (1) bal-
anced. If the pressure differential ΔpDW is increased to above bar, the pressure compensator will
be re-opened as in front of the valve opening, 30 bar are no longer achieved.
The pressure compensator is in a control position.
The pressure in front of the valve opening is controlled to 30 bar.
As the load pressure pL amounts to 20 bar, the pressure differential ΔpV at the valve opening is
10 bar.
When the load pressure changes, the pressure compensator will also change the control posi-
tion until a pressure differential ΔpV = 10 bar is reached.
If the pressure pP changes, the pressure compensator will change the control position in this
case, as well, until a pressure differential ΔpV = 10 bar is reached.
That means that the pressure compensator compensates all pressure changes.
By means of the control spring, the pressure differential ΔpV at the metering orifice A1 is
kept constant.
In systems with pressure compensators, the pump controller setting must exceed the setting of
systems without pressure compensators by the control pressure differential. The pressure com-
pensator of actuator 1 with the lower load pressure generates a pressure differential ΔpDW of
90 bar and keeps the pressure differential ΔpV = pV1 – pL1 = 30 – 20 = 10 bar constant.
With the pressure compensator, the annoying behavior with different load pressures no longer
exists as the pressure differential ΔpV1 = ΔpV2 = 10 bar remains constant.
The pressure compensator of actuator 2 with the high load pressure generates a pressure dif-
ferential ΔpDW = 10 bar.
Fig. 0-13: Individual pressure compensators in the load sensing system
= 100 bar
ΔpDW = 10 bar
ΔpV2 = 10 bar
pV2 = 110 bar
pL2 = 100 bar
= 20 bar
pL1 = 20 bar
ΔpV1 = 10 bar
pV1 = 30 bar
ΔpDW = 90 bar
Control spring
= 10 bar
pP = 120 bar
pP = 120 bar

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Actuator flow and stroke limitation
For simplification, we have until now always assumed a constant valve opening d = 5 mm.
In the control block, the valve opening A with the control spool stroke and the control
grooves can be selected by the operator using the operating levers.
As the pressure differential Δp at the control grooves is kept constant by the pressure
compensator, the position of the operating lever always corresponds to the same velocity,
regardless whether with or without load, in individual and parallel operation (in the satu-
rated condition).
With stroke limitations, the maximum flow rates of the individual actuators can be set, e.g.
the max. actuator flow shall only be 60 l/min instead of the possible 100 l/min. Using the
set screw, the control spool stop is adjusted so that only 60 % of the stroke are possible.
In this regard, it has to be considered that 40 % of the possible control stroke can no
longer be utilized.
If now, only 25 l/min shall flow, only 25 % of the control stroke are available. This resolu-
tion is quite bad and may often be reflected in bad controllability.
For good controllability, the actuator velocity is to be resolved to the largest control spool
stroke possible.
That is way control spools with graduated flow rates are available.
A spool E25/25 has, with a stroke of 100 %, a flow in A and B of 25 l/min each. In the
same way, the resolution deteriorates if spools for 100 l/min are used with a pump deliv-
ery volume of 50 l/min. In this case, there will be no more velocity increase from 50 % of
the stroke, i.e. 50 % of the control stroke are not utilized.
The control pressure differential Δp is not achieved. The pressure compensator opens
from 50 % of the control stroke.
Notes

13
50 % 100 %
100 %
50 %
0 %
Fig. 0-14: Control range
Spool stroke
qActuator
Control range
Stroke limitation 60 %
q pump 50 %
q = f (A)
Δp1 = Δp2

Bosch Rexroth AG
Load sensing pressure limitation (LS)
In individual cases in which certain actuators must not work with the maximum system
pressure, the actuator pressure must be limited.
You can do so using the secondary pressure relief valves. When the actuator pressure
is reached, the entire actuator flow will then, however, be discharged to the tank (high
power loss).
By means of limitation of the LS pressure, the pressure in the spring chamber of the pres-
sure compensator is limited. If the actuator pressure has been reached, the pressure in
the spring chamber will stop increasing and the pressure compensator closes.
There is only a relatively small pilot oil flow of approx. 2.5 l/min.
q actuator greater than q pump
The operating limit of a load sensing system has been exceeded if the entire actuator
volume requested by the directional valves is greater than the maximum displacement of
the pump possible. In this case, the pump is in the maximum stop. The required system
pressure for the actuator with the highest load pressure can no longer be maintained as
the oil preferably flows to the actuator with the lower load pressure.
For the actuator with the highest load pressure this means that it is only supplied with the
residual oil quantity or it also stops completely, if applicable.
Both actuator valve openings are opened for 100 l/min.
The maximum pump delivery volume is only 100 l/min, the system is under-supplied. Cyl-
inder 1 has a load pressure of 20 bar and cylinder 2 has a load pressure of 100 bar. Both
pressure compensators are completely open as the pressure for closing the pressure
compensators is not achieved.
The resistance of valve opening 1 is not sufficient for generating a pressure differential Δp
= 10 bar. The pressure compensator cannot be closed with 28 bar. This is only possible
from 30 bar. The pressure loss of a completely opened pressure compensator is only
minor and thus, the system pressure is now also on the lower level of 28 bar.
For the actuator 2 with a load pressure of 100 bar, this means standstill. If actuator 1 is
only open for 75 l/min, 25 l/min remain for actuator 2.
In this case, there resistance of valve opening 1 is sufficient for generating a pressure dif-
ferential Δp = 10 bar and closing.
Now, the system pressure can rise to values above 100 bar and move cylinder 2.
When operating a machine, this behavior may be annoying; therefore, the delivery volume
of the pump in the load sensing system must always be sufficient for all simultaneously
operated actuators.
Example

15
Load pressure-independent flow distribution (LUDV)
Full supply in the LUDV system
With the Load pressure-independent flow distribution (LUDV) system, the velocity of all
actuators is reduced in the same ratio in case of undersupply.
In the example specified above, every cylinder would be operated with 50 l/min.
In the LUDV system, the pressure compensators are located downstream the metering
orifice and they are all provided with the highest load pressure.
The pressure compensators are symmetrical spools without spring.
The load pressure acts in the closing direction. The pressure after the valve opening acts
in the opening direction.
If the pressure in front of the pressure compensator (after the valve opening) is larger than
the load pressure, the pressure compensator starts to open. In this way, this pressure
always corresponds to the highest load pressure.
The displacement controller of the pump controls the pump pressure pP to a value 10 bar
higher than the load pressure.
Fig. 0-15: Undersupply in the load sensing system
Z1 = 20 bar Z2 = 100 bar

↑qP =
100 l/min
= 10 bar 10 bar =
↑qV1 =
100 l/min
qV2 =
0 l/min ↑
qP qV1 + qV2 (controlled)
= 0 bar
100 bar
28 bar
28 bar
20 bar
8 bar
= 100 l/min
= 100 l/min
28 bar

Bosch Rexroth AG
Undersupply in the LUDV system
If there is an undersupply, the pump is maximally deflected. Due to the reduced pressure
differential Δp at all valve openings, a reduced flow results. The closing of both pressure
compensators prevents the standstill of both actuators.
As the reduced pressure differential Δpred. is the same again at all valve openings, the flow
rates are in the same ratio again, as well.
Important:
If the LUDV system returns into the full supply from the undersupply (command value
cancellation), the actuators are accelerated. This unwanted acceleration is not admis-
sible with mobile machines (e.g. crane) (see EN 13000).
Calculation reduced flow qred.:
Σ Σ
Σ
q q
q
1 2
100 50
+ +
= = 150 l/min = 100 %
=
100
1,
red.
5
5
50
1,5
= 100 l/min
= 66,7 = 100 l/mi
+
+
Σqred.
,
33 3 n
n = 100 %
Fig. 0-16: Full supply in the LUDV system
20 bar
= 20 bar = 100 bar
100 bar
= 80 bar = 0 bar
100 bar
100 bar
Δp1 = 10 bar
pP = 110 bar
qV1 =
↑
50 l/min
qP = 100 l/min
Δp1 = Δp2
Δp2 = 10 bar
qV2 = 50 l/min
10 bar
= 50 l/min 50 l/min =

17
Delivery volume of the pump qmax. = 100 l/min.
If only actuator 1 is operated, the pressure differential Δp at the valve opening is 10 bar
and the flow is 100 l/min.
If only actuator 2 is operated, the pressure differential Δp at the valve opening is 10 bar
and the flow is 50 l/min.
If the actuators 1 + 2 are operated, the system is undersupplied as the pump delivery
volume with 100 l/min is not sufficient for both actuators = 150 l/min.
The actuator flows are reduced in the ratio of the undersupply 1 : 1.5.
The reduced actuator flows are 100 / 1.5 = 66.7 l/min and 50 / 1.5 = 33.3 l/min.
The calculation results in Δpred. = 4.4 bar.
In practice, the reduction of the actuator flow rates takes effect correspondingly faster in
case of fast actuation of the second actuator and may lead to an abrupt deceleration of
the first actuator.
Disadvantage: If the command values are canceled, the actuators are accelerated.
Example
Fig. 0-17: Undersupply in the LUDV system
20 bar
= 20 bar = 100 bar
100 bar
= 80 bar = 0 bar
100 bar
100 bar
Δp1 = 4.4 bar
= 100 l/min
qV1 =
↑
66.7 l/min
Δp1 = Δp2 = Δpred.
Δp2 = 4.4 bar
qV2 = 33.3 l/min
10 bar
pP = 104.4 bar
qP = 100 l/min
50 l/min =

Bosch Rexroth AG
Primary and secondary pressure valve
The primary pressure valve is located at the input element. This pressure relief valve is
used to set the maximum system pressure in channel P.
The secondary valve is installed in the actuator ports. This pressure relief valve is used
to limit the max. actuator pressure. The secondary valves are used as protection against
pressure peaks and external forces; they take effect when the control spool is not oper-
ated.
Secondary valves are designed as pure pressure valves or as valves with pressure and
feed function. The feed function is a check valve that opens when the pressure in the
actuator is lower than the pressure in channel T.
This function is important in order to prevent vacuum and cavitation in the actuators.
Vacuum in cylinders results in air separations from the oil leading to seal damage and
unwanted delays in the working behavior of the machine.
Vacuum in hydraulic motors leads to cavitation destroying the motor and the machine may
completely get out of control.
This is very dangerous with winches and carriages; for safety reasons, there is therefore
additional safety equipment like lowering brake valves in order to prevent this.
Hydraulic pilot control
The operation with mechanical handle-operated levers requires the operator to be directly
at the control block.
With many construction machines, the control block is in a central position and the con-
struction machine operator sits in a cabin having good view of the working area.
An operation using rods is too inflexible and complex.
With most construction machines, the operating elements e.g. hydraulic pilot control units
are integrated in the driver's seat armrest and in this way allow for comfortable operation
of the machine.
The signal is transmitted by means of hydraulic pressure from the hydraulic pilot control
unit to the control spool.
In the hydraulic pilot control unit, a pressure reducing valve is used to set a pressure con-
tinuously, depending on the characteristic curve, from 6 to 24 bar. This pilot pressure acts
on the pilot spool that is clamped by the centering springs.
The spring force increases with an increasing stroke.
Proportionately to the lever deflection of the pilot control unit, a pilot pressure is gener-
ated that again adjusts the directional valve main spool until the forces at the directional
valve spool are balanced.

19
1 Housing
2 Main spool
3 Pressure compensator
4 LS pressure limitation valve
5.1 Secondary shock/feed valve
5.2 Plug screw
6.1 A side stroke limitation
6.2 A side stroke limitation
6.3 B side stroke limitation
7 LS shuttle valve
8 Spring chamber
9.1 Pressure reducing valves
(Pilot control valve a)
9.2 Pressure reducing valves
(Pilot control valve b)
10 Handle-operated lever
Function LS control block M4-12
The sectional drawing shows a directional valve element with mechanical and
electrohydraulic actuation.
Mechanical operation (see figure 0-18)
Using the handle-operated lever (10), the main spool (2) can be operated in
both directions.
The stroke limitations (6.1, 6.2, 6.3) can be used to set the maximum flow rate.
Two set screws (6.1 or 6.2) influence the flow of P → A, one set screw (6.3) the
flow P → B.
Fig. 0-18: Sectional drawing control block M4-12
Cover B
Cover A

Bosch Rexroth AG
Hydraulic and electrohydraulic operation (see figure 0-18)
The hydraulic pilot pressure can either be controlled using the hydraulic pilot control unit
4TH6 or using the electrical pressure reducing valves (9.1, 9.2).
The hydraulic control connections are always located in the cover A. Through a bore in
the housing, the pilot pressure reaches the cover B.
The pilot oil supply X comes from the input element into which a pilot oil supply has been
installed.
The pilot oil drain Y must be led to the tank at zero pressure.
Using the main spool (2), the flow direction is controlled and using the stroke the
flow rate.
Apart from that, the load pressure is recorded by means of bores in the main spool (2).
Grooves are milled into the main spool (2), the opening cross-section of which determines
the flow rate in the supply and also the flow rate to the T channel.
Pressure compensators (see figure 0-18)
The pressure compensator consists of a spool (3) with milled-in grooves and a bore for
recording the pressure in front of the main spool (2). The spool (3) is loaded with a spring
determining the pressure differential Δp at the main spool.
By means of shims, the spring force and consequently the pressure differential Δp and
thus the maximum flow with identical opening cross-section of the valve can be changed.
The pressure compensator shown has moreover a load holding function. This prevents the
lowering of the load if the pressure in P is less than the load pressure.
LS signal (see figure 0-18)
The LS signal is recorded by bores in the main spool and led into the pressure compensa-
tor spring chamber. In this area, the LS signal can be limited by means of the LS pressure
relief valve for every actuator port. At the measuring points MA and MB, the LS pressure
can be measured or also influenced by means of external valves.
The LS signal is forwarded to the pump controller via the shuttle valve (7).
Pressure limitation (see figure 0-18)
The actuator ports A and B can be protected from excessive pressure by means of sec-
ondary pressure valves (5.1). The secondary valve shown is not adjustable.
It simultaneously offers a feed function by acting as check valve of T → A.
The plug screw (5.2) is necessary if neither the pressure limitation nor the feed-in is nec-
essary.

21
Input element (see figure 0-18)
The input element accommodates the primary pressure valve and the pilot oil supply.
P line, T line, LS line and pilot oil line (X, Y) are connected at the input element.
There are input elements in different designs (see data sheet RE 64276).
End elements
In the end elements, the LS pressure is discharged. Alternatively to the discharge, there
may be an external LS port for more LS actuators.
Discharge of the LS pressure to the tank in the non-operated condition of the directional
valves is important for the failure-free functioning of the system. In this connection, the
pump's displacement controller is notified a low pressure level (standby pressure).
This must also be ensured with an external LS connection (see data sheet RE 64276).
Fig. 0-19: Circuit diagram M4-12
1 Housing
2 Directional valve main spool
4 LS pressure relief valve
5
Secondary pressure relief valve (with
cavitation protection) and plug screw
6 Stroke limitation
7 Shuttle valve
8 Handle-operated lever
9 Proportional pressure reducing valve
1
8
6

Bosch Rexroth AG
Function LUDV control block SX-12
The sectional drawing shows a directional valve element with mechanical actuation.
Mechanical operation (see figure 0-20)
The main spool (2) can be operated in both directions.
Stroke limitations are not provided.
Hydraulic operation (not shown)
The hydraulic pilot pressure can be set using the hydraulic pilot control unit 4TH6. With
hydraulic actuation, stroke limitations are possible.
The hydraulic control connections are located in the covers.
Main spool (see figure 0-20)
Using the main spool (2), the flow direction is controlled and using the stroke the
flow rate.
Grooves are milled into the main spool (2), the opening cross-sections of which determine
both, the flow rate in the supply and the flow rate to the T channel.
Fig. 0-20: Sectional drawing control block SX-12
1 Housing
2 Main spool
3 Check valve
5 Secondary valve
6 Plug screw

23
Pressure compensators (see figure 0-20)
The pressure compensator consists of a spool (4) with milled-in grooves and a bore for
recording the pressure after the main spool (2).
The spool (4) is symmetrical and not loaded with a spring.
The pressure differential Δp at the main spool is determined by the pump controller and in
case of undersupply results due to reduced flows. (See basics)
The check valves (3) have the load holding function. This prevents the lowering of the load
if the pressure in P is less than the load pressure.
LS signal (see figure 0-20)
The load pressure is recorded by means of a bore in the spool of the pressure compensa-
tors (4).
The pressure compensator of the actuator with the highest load is always complete-
ly open.
Only in this case is the bore open.
That means that only the load pressure of the actuator with the highest load is recorded
and forwarded to the pump and the other pressure compensators.
The pressure compensators of the actuators with lower load pressure are in a control
position in which the bore is overlapped.
Shuttle valves are therefore not required.
Pressure limitation (see figure 0-20)
The actuator ports A, B can be protected from excessive pressure by means of secondary
pressure valves (5). It simultaneously offers a feed function by acting as check valve of T
→ B.
The plug screw (6) is screwed in if neither the pressure limitation nor the feed-in is neces-
sary.
Input element (see figure 0-20)
The input element accommodates the primary pressure limitation and the LS unloading.
The primary pressure limitation is effected by limiting the LS signal.
As option, the input element can be equipped with a flushing valve, opening a connection
P → T.
The P line, T line, LS line and pilot oil X, Y are connected at the input element.
There are input elements in different designs (see data sheet RE 64128).
End elements
As end element, there may be an end plate or a plate with additional port P3 (see data
sheet RE 64128).

Bosch Rexroth AG
Notes

25
RE 09970/03.11 I Safety instructions Bosch Rexroth AG
General safety instructions
So that the possible dangers of machines and systems are recognized, safety regulations,
product information and operating instructions must be observed.
Trainer must make the necessary documentation available to the trainee. When us-
ing competitive products, the safety instructions prescribed by the manufacturer apply,
whereas it has to be ensured that the components and systems comply with the currently
valid and relevant EU directives.
The commissioning is therefore prohibited until it was confirmed that the elec-
trohydraulic components and systems that are to be used comply with the pro-
visions of all relevant EU directives.
General, basic safety instructions
Then following is to be observed:
• Danger warnings and safety instructions at the machine,
Operating instructions
• regulating the behavior during operation in order to avoid
accidents and damage to health, which are to be prepared by the operator / employer
e.g. on the basis of accident prevention regulations
Operating instructions
• ensuring the proper, intended use of the hydraulic system.
The operating instructions are to provide information and avoid dangers when
installing the hydraulic components into the system – in this case the installa-
tion of the electrohydraulic components into the practice stand - and it provides
information and notes for transport, storage and maintenance (inspection, ser-
vice, repair) of the hydraulic system.
Only in case of strict compliance with the operating instructions can accidents
and damage to property be avoided and failure-free operation of the hydraulic
system be guaranteed.
Apart from that, compliance with the operating instructions results in:
Reduced down times and repair costs
•
Increased service life of the hydraulic system.
•
Warning
Warning

26 Safety instructions I RE 09970/03.11
Bosch Rexroth AG
Hydraulic oil on mineral oil basis is water-endangering and inflammable. It may only
be used if the corresponding safety data sheet is available and all measures prescribed
therein have been realized.
The hydraulic system may only be operated in a technically unobjectionable condition.
The intended use, performance data and operating conditions must not be changed.
You must not decommission protective devices / components, e.g. by bridging end
switches, valves and other control components.
If for maintenance works, protective devices have to be bridged, safety measures have
to be taken in advance which guarantee that no dangerous situation can result. The supe-
rior machine operating instructions have to be observed.
The operation of adjustment equipment at components and/or changes at program-
mable control systems may only be carried out by authorized personnel within the scope
of the intended use of the hydraulic system.
In an emergency, in case of error or other irregularities:
Hydraulic systems are to be switched off and the main switch is to be secured against
•
re-activation,
The danger zone is to be secured so that nobody can access the danger zone in an
•
uncontrolled form and without this being known,
Responsible specialists must be informed immediately.
•
Uncontrolled access of company-external persons to the direct operating‑area of the
hydraulic system (also if the hydraulic system stands still) is forbidden.
Important:
Those are general safety provisions that have to be observed in detail in every proj-
ect task.
Air may be available in hydraulic oils in the following forms: As dissolved air (invisible), as
surface foam (visible) and as undissolved, dispersed air (visible). While dissolved air and
a little bit of surface foam have hardly any disadvantageous effects, dispersed air can lead
to major problems. As the oil contains very small air bubbles in a very finely dispersed
form that can only rise to the surface very slowly, the following faults may occur:
Unequal or jerky movements of the hydraulic pistons, vibration in the system due to an
•
increase in the compressibility, changed actuating times of servo valves
Noise in the pump
•
Cavitation damage at pumps, lines and seals
•
Accelerated aging of the oil
•
Microdiesel effect, one form of thermal cracking due to high temperatures in com-
•
pressed small air bubbles
Effects of air
in the oil

27
RE 09970/03.11 I Safety instructions Bosch Rexroth AG
In order to avoid undissolved air in the oil, the following has to be observed: Leak-tight-
ness of the system on the suction side, perfect size of the storage tank, installation of
baffles in the oil storage tank, favorable design of the suction system without throttling
points, sufficient oil level, low oil circulation speeds, submersible pumps instead of high
suction heads.
Hydraulic systems are closed systems. I.e. in case of intended use, the hydraulic oil is not
released in the environment. Leak-tightness of the units and timely maintenance / repair
have to be ensured. Particularly hydraulic hoses and hose connections are to be closely
monitored and checked. The oil change has to be completed appropriately and profession-
ally; the used oil has to be disposed of complying with all legal provisions.
Hydraulic fluids on mineral oil basis are water-endangering and inflammable.
Hydraulic fluids may only be used if the corresponding safety data sheet of the
manufacturer is available and all measures prescribed therein have been real-
ized.
If leakage at the hydraulic product can lead to water and soil contamination, the
hydraulic product must be put into a suitable drain tray.
One of the basic prerequisites for the failure-free operation of a hydraulic system is the
unobjectionable condition of the hydraulic fluid as pollution still is one of the main reasons
for failure of hydraulic components. The following sketch shows different types of pollution
that may lead to pollution of the hydraulic fluid.
Environmental
aspects
Safety aspects
Danger
Filtration
Notes

28 Safety instructions I RE 09970/03.11
Bosch Rexroth AG
Fig. 0-22: Sources of pollution
1 External pollution
2 Assembly + Repair
3 New oil
4 Wear debris in pump
5 Wear debris of seals
The technical data sheets of the component manufacturers include information on the
evaluation of the solid share in the hydraulic fluid by means of classification ‑ systems
(standardized cleanliness classes).
Today, the standards NAS 1638 (National American Standard) and ISO DIS 4406 are
most widely used.
Today, specification of the filtration rating in μm is no longer common; it is, however, still
frequently used in the preparation of circuit diagrams.
Important:
The detailed topic Filtration and maintenance is not dealt with in the mobile hydraulic
project manuals.
The sources of information mentioned in this project manual like data sheets, operating
instructions and reference books contain information on the Filtration topic.
Classification

29
RE 09970/03.11 I Operation LS unit Bosch Rexroth AG
Operation load sensing (LS) unit
• Displacement-controlled vane pumps (2.1)
Pressure relief valves 70 bar (2.32, 2.52); type-tested
•
Return line filter (3.0)
•
Connection blocks with plug-in couplings for P1-3, T1-2, LS
•
3-way ball valves (7.1, 7.2)
•
LS pressure relief valves (2.0)
•
Measuring ports MP1, MX
•
The 3-way ball valves (7.1, 7.2) are in position P → L (lever downwards).
In this position, the line from the pump is blocked and the connection block to the leakage
oil is unloaded and depressurized.
After switch-on of the electric motor, the pumps are controlled to a pressure of 15 bar. By
operation of the 3-way ball valve by 90°, the connection block P is connected with P1 of
the pump (operating position).
Without pressure in port LS, the pressure P remains at 15 bar, according to the spring
value at the displacement controller X.
In order to get a higher pressure in P, a pressure signal must be available at the port LS.
Together with the spring, this LS pressure acts on the displacement controller X.
The pressure P is therefore always 15 bar higher than the LS pressure.
If the LS pressure is taken from port P1, the pump behaves like a pressure-
controlled pump.
The controlled pump pressure is set using the LS pressure relief valve (2.0).
In order to prevent overloading of the LS pressure relief valve (2.0) with excessive flow, a
limitation nozzle 0.8 (3.0) has been installed upstream.
The LS pressure relief valve (2.0) has a 50 bar compression spring.
With max. load, a controlled pressure P of 65 bar can be set.
In practices with constant pressure (industrial hydraulics), the LS pressure must be taken
from P1.
The controlled pressure P is set to 50 bar using the LS pressure relief valve (2.0).
In practices with load sensing (mobile hydraulics), the LS pressure must be taken from the
LS port of the control blocks used.
The control pressure is set to 60 bar using the LS pressure relief valve (2.0).
In the rest position (lever vertically downwards), the connection block to the leakage oil is
unloaded and the P line is blocked.
In the operating position (lever horizontal), the 3-way ball valve is used to connect the con-
nection block P with P1 or P2 pump.
The pressure P only amounts to 15 bar and increases very slowly after the 3-way ball
•
valve has been brought into operating position.
Cause: No LS pressure at controller X (measuring point MX)
•
→ In this case, the LS pressure will only rise above the controller spool leakage.
Constant pressure: No connection established from P1 to LS
•
Load sensing: LS connection not established
•
Nozzle 0.8 (3.0) blocked
• → Remove the LS coupling connector and check and clean
the nozzle, if necessary.
Set-up
Function
Operation in
training mode
Error possibilities

30 Operation LS unit I RE 09970/03.11
Bosch Rexroth AG
Setting instruction for external control block pressure relief valve
(primary pressure relief valve)
For setting the maximum working pressure, an external pressure relief valve DD1.N-W
(item 02) is used for didactic reasons.
Valve setting procedure:
Connect port P1 with the LS port at the connection block.
1.
Establish the measuring points MP and MP1.
2.
Connect the pressure relief valve at port P2 and port T via the distributor with port T2
3.
at the connection block.
Switch on the training system.
4.
Bring the 3-way ball valve (item 7.1, 7.2: from the rest position into the operating
5.
position (lever horizontal).
Set the control block pressure relief valve to 40 or 50 bar (value varies depending on
6.
the practice).
Important:
The primary valves that are usually installed in the SM12 control block are set at the test
stand with a flow qV = 5 l/min and 55 °C oil temperature.
Setting instruction for pre-filling pressure of the hydraulic accumulator
The diaphragm-type hydraulic accumulator must be filled before every commissioning or
practice with nitrogen (not included in scope of delivery) to the necessary, gas-side pre-
filling pressure (p0 = 15 to 18 bar) or unloaded accordingly. For this purpose, the filling
and test equipment for hydraulic accumulators is necessary (Mat. no. R900001439; not
included in the standard scope of delivery).
Important:
The hydraulic accumulator used in the training system may be operated with the follow-
ing pressure ratio:
Operating pressure p / pre-filling pressure p
• 0 → 8 : 1
(e.g. max. operating pressure x jcyl. = 60 bar x 1.69 = 101.4 bar → p0 = 13 bar
Attention: In case of improper use, the hydraulic accumulator may be destroyed!

31
RE
09970/03.11
I
Practice
Bosch
Rexroth
AG
Circuit
diagram
load
sensing
unit

32 Practice I RE 09970/03.11
Bosch Rexroth AG
In this practice, the behavior of a constant pressure system with throttle valve and change-
able load is to be worked out.
The practice is important to identify the function of displacement-controlled pumps in the
constant pressure system.
Fig. 0-23
Size 4
Unit limit
70 bar
Practice with constant pressure system

33
RE 09970/03.11 I Practice Bosch Rexroth AG
• The pump is a displacement-controlled vane pump V7 (1).
Using the throttle valve (2), the delivery volume is set to 5 l/min.
•
The load is changed using the pressure relief valve (3).
•
Using the pilot pressure relief valve (4), the maximum pump pressure is set.
•
In the supply of the pilot pressure relief valve (4), a nozzle 0.8 mm has been installed.
•
The actuator volume is measured by means of a flow meter (5).
•
The pump has two control spools max. and min. and one controller (7).
The max. spool has a larger diameter and is moreover spring-loaded so that the pump can
deliver upon start-up.
The min. spool has a smaller diameter and is connected with P.
The controller (7) is kept in the position P → max. by a spring. In this position, the max.
spool is loaded with pressure from P. The stroke ring is moved in the displacement direc-
tion until the pressure P is greater than the pressure X + spring value. If the pressure P is
greater, the controller spool (7) is moved and the max. spool is unloaded. The stroke ring
is now moved from min. spool in the zero stroke direction. If the pressure P falls below the
pressure X + spring value, the controller spool (7) is pushed back by the spring and the
stroke ring moves back in the displacement direction. The control spool (7) controls the
stroke ring position.
The control pressure LS is recorded in front of the throttle (2) and corresponds to the
pressure P.
The pilot pressure valve (4) limits the pressure after the supply nozzle 0.8 and forwards it
to the controller (7).
As the pressure in P corresponds to the pressure in X, the stroke ring is maintained at max.
displacement until the pilot pressure relief valve (4) opens and limits the pressure X. The
nozzle 0.8 is necessary for the pilot oil limitation and the pressure drop in X.
Pressure X corresponds to pressure P minus the spring value.
Using the pilot pressure relief valve (4), the pressure P can be remotely adjusted.
The pilot pressure relief valve (4) is absolutely necessary as otherwise, the stroke ring is
not moved to zero stroke. In this case, the pump pressure would increase until the safety
pressure relief valves (6) open. If the entire delivery volume is discharged to the tank via
the safety pressure relief valves (6), the oil heats up considerably.
Set-up according to circuit diagram.
The flow meter must be installed after the load pressure relief valve in order to record the
actuator volume.
It is important to measure the pilot pressure in front of the throttle.
Unload the pressure relief valves (3, 4).
1.
Open the throttle valve (2) completely.
2.
Switch on the pump, bring the 3-way ball valve into operating position.
3.
Close the throttle valve (2).
4.
Use the pilot pressure relief valve (4) to set a pressure P = 50 bar.
5.
Use the throttle valve to set the flow rate to 5 l/min, with unloaded load pressure valve
6.
(3).
Use the load pressure valve (3) to increase the load pressure in 5 bar steps.
7.
Enter the pressures
8. p, pL, pX and the flow values qV into the table.
Calculation of the pressure differential
9. Δp at the throttle and the power loss with
Pv = qV • ΔpDr / 600.
Components
Function
Practice
implementation

34 Practice I RE 09970/03.11
Bosch Rexroth AG
Using the pilot pressure relief valve (4), the pressure p can be adjusted.
The pressure in the line P and the pressure pX are always almost constant.
Using the throttle valve (2), the flow 5 l/min can be set.
If the load pressure is increased, the flow continuously decreases as the pressure differ-
ential Δp at the throttle decreases.
With low load pressure, the power loss is highest.
Important:
With real machine for example, the pressure in line P is 250 bar and the delivery vol-
ume is 100 l/min.
Here, the power loss with low load pressures is much higher.
250 bar • 5 l/min / 600 = 2 kW or 250 bar • 100 l/min / 600 = 41.7 kW
Result
Fig. 0-25
Device
arrangement
pL
(in bar)
p
(in bar)
pX
(in bar)
qV
(in l/min)
ΔpR
(in bar)
ΔpDr
(in bar)
PV
(in kW)
5 48.8 35.1 5 13.7 43.8 0.365
10 49 35.1 4.7 13.9 39 0.31
15 49.1 35.1 4.4 14 34.1 0.25
20 49.2 35.1 4.0 14.1 29.2 0.19
25 49.4 35.2 3.6 14.2 24.4 0.15
30 49.5 35.2 3.1 14.3 19.5 0.10
35 49.6 35.1 2.6 14.5 14.6 0.06
40 49.8 35.1 2.1 14.7 9.8 0.03
45 50 35.2 1.4 14.8 5 0.01
Fig. 0-24: Table 1 (DR)

35
Practice with load sensing system
In this practice, the behavior of a load sensing system with throttle valve under the influ-
ence of changeable load is to be worked out.
The practice is important to identify the function of displacement-controlled pumps in the
load sensing system.
Fig. 0-26
Size 4
Unit limit
70 bar

36 Practice I RE 09970/03.11
Bosch Rexroth AG
• The pump is a displacement-controlled vane pump V7 (item 1.0).
Using the throttle valve (item 2.0), the delivery volume is set to 5 l/min.
•
The load is changed using the pressure relief valve (item 3.0).
•
Using the pilot pressure relief valve (
• item 4.0), the maximum pump pressure is set.
In the supply of the pilot pressure relief valve (item 4.0), a nozzle with a diameter of
•
0.8 mm is installed.
The actuator volume is measured by means of a flow meter (item 5.0).
•
The V7 pump has a controller (item 7.0) and two control spools with different diameter.
The spool with the smaller diameter is connected with port P. The spool with the larger
diameter is spring-loaded in order to bring the stroke ring in idle run into an eccentric
position. Consequently, pump delivery upon start-up is possible.
A spring keeps the controller (item 7.0) in the position p → max. In this position, the larger
spool is loaded with pressure from line P. The stroke ring is moved in the displacement di-
rection until the pressure p is greater than the pressure pX + spring value. If the pressure
p is greater, the controller spool is moved and the larger spool is unloaded. The stroke
ring is now moved from the smaller spool in the zero stroke direction. If the pressure p
falls below the pressure pX + spring value, the controller spool is pushed back by the
spring and the stroke ring moves back in the displacement direction. The control spool
controls the stroke ring position.
The pilot pressure X is measured after the throttle (item 2.0) and corresponds to the pres-
sure pL.
The pressure pL = pX with an unloaded load pressure valve corresponds to approx. 0 bar.
The pressure p moves the control spool against the control spring on position P → L and
the larger spool is unloaded, the pressure p moves the stroke ring on zero stroke. The
spring value corresponds to the zero stroke pressure.
The pressure p therefore always exceeds the pressure pLS, namely by the spring value.
The pressures pX and pLS always fall below the pressure p, namely by the spring value.
In this way, the pressure differential Δp at the throttle is kept constant.
Using the pilot pressure relief valve (item 4.0), the pressure after the supply nozzle is
limited. Opening this valve limits the pressure pX. The nozzle (0.8) is necessary for limiting
the pilot oil and for the pressure drop at port X.
Using the pilot pressure relief valve, the maximum pressure at port P can be set.
The pilot pressure relief valve (item 4.0) is absolutely necessary as otherwise, the stroke
ring is not moved to zero stroke. In this case, the pump pressure would increase until the
safety pressure relief valves (item 6.0) open. If the entire delivery volume is discharged to
the tank via the safety pressure relief valves, the oil heats up considerably.
Set-up according to circuit diagram.
Components
Function
Practice
implementation

37
pL
(in bar)
p
(in bar)
pX
(in bar)
qV
(in l/min)
ΔpR
(in bar)
ΔpDr
(in bar)
PV
(in kW)
5 19.4 5.7 5 13.7 14.4 0.12
10 24.5 10.8 5 13.7 14.5 0.12
15 29.4 15.7 5 13.7 14.4 0.12
20 34.4 20.7 5 13.7 14.4 0.12
25 39.4 25.7 5 13.7 14.4 0.12
30 44.4 30.7 5 13.7 14.4 0.12
35 47.8 34 4.3 13.8 12.8 0.09
40 49 34.7 3 14.3 9 0.05
45 49.6 35 1.4 14.6 4.6 0.01
Fig. 0-27: Table 1 (LS)
Device
arrangement
Fig. 0-28
The flow meter must be installed after the load pressure relief valve in order to record the
actuator volume.
It is important to measure the pilot pressure after the throttle.
Unload the pressure relief valves (3,4).
1.
Open the throttle valve (2) completely
2.
Switch on the pump, 3-way ball valve in operating position
3.
Screw in the load pressure relief valve (3) to stop (max. pressure)
4.
Using the pilot pressure relief valve (4), set
5. p = 50 bar
Unload the load pressure relief valve (3) completely again (min. pressure)
6.
Using the throttle valve (2), set 5 l/min, with unloaded load pressure valve (3)
7.
Use the load pressure valve (3) to increase the load pressure in 5 bar steps.
8.
Enter the pressures
9. p, pL, pX and the flow values qV into the table
10. ΔpR = p – pX at the pump controller, the pressure dif-
ferential ΔpDr = p – pl at the throttle, the power loss at the throttle with Pv = qV • ΔpDr/600.

38 Practice I RE 09970/03.11
Bosch Rexroth AG
Using the pilot pressure relief valve (4), the maximum pressure p can be limited.
The pressure differential ∆p at the throttle valve is constant until the maximum pump pres-
sure is achieved.
Using the throttle valve (2), the flow 5 l/min can be set.
If the load pressure is increased, the flow remains almost constant as long as the pres-
sure differential ∆p at the throttle remains constant.
If the maximum pump pressure is reached, the pilot pressure pX is limited and the pres-
sure differential ∆p at the throttle and the flow decrease.
A load sensing system only functions if the pressure differential ∆p at the throttle can be
kept constant.
If the maximum pump pressure set is achieved and the load pressure continues to in-
crease, the pressure differential decreases and the flow delivered to the actuator decreas-
es.
Important:
With real machines, the pressure p is e.g. 250 bar and the delivery volume is 100 l/min.
Here, the constantly low power loss for energy saving has very positive effects.
20 bar • 5 l/min / 600 = 0.17 kW or 20 bar • 100 l/min / 600 = 3.3 kW
•
Using the spring pretensioning at the displacement controller (item 7.0), the pressure
differential ∆pR can be changed.
Result
Notes

1
RE 09970/03.11 I Project 01: Primary pressure limitation Bosch Rexroth AG
01
Project 01: Primary pressure limitation
Project definition
A large rotary drill is operated with a load sensing control for the top drive and the cylinder
feed.
Settings are to be made in the commissioning.
The maximum system pressure is to be limited so that the device cannot be overloaded.
The maximum safety pressure is set using the primary pressure valve.
The maximum operating pressure is set using the load sensing pressure limitation (LS-
DB) at the connection block.
Project tasks
The differences between the pressure limitations are to be worked out.
•
Determination of the correct order when setting the pressures.
•
Find the location of the set screws.
•
Measuring and setting the pressures.
•
Determine the system behavior of the different pressure limitations with primary pres-
•
sure valve and LS-DB.
Fig. 01-1: Drill in operation

2 Project 01: Primary pressure limitation I RE 09970/03.11
Bosch Rexroth AG
01
Project steps
• Information: What is the current condition of the machine?
What exactly is to be done?
• Planning: Selecting and inspection documents for information.
Component selection.
Where are the components, set screws and measuring
points located?
Preparation of the hydraulic circuit diagram.
• Decision-making: How must the components be connected with each other in
order to realize the requirements?
• Execution: Setup of the hydraulic control.
Setting the required values and their documentation.
• Checks: Are the required values achieved?
• Evaluation: How is the system behavior?
Notes

3
01
Circuit diagram hydraulic power unit
Fig. 01-2: Hydraulic circuit diagram
Unit limit
70 bar
Size 4

Bosch Rexroth AG
01
Circuit diagram hydraulic set-up
Measuring glass
Size 4

5
01
Component select with parts list
item Quantity Device designation Type designation
01 1 Load sensing mobile control block 2M4-12
02 1 Pressure relief valve DD1.1
03 1 Distributor DZ4
04 1 Flow meter + Multi-handy DZ30
09 1
Pressure gauge with measuring hose
(or digital pressure sensor)
DZ1.4
5 Hose line 90° 1000 mm DKO/DKO90x1000
1 Hose line 90° 2000 mm VSL3.1
1 Hose line 630 mm VSK1
Fig. 01-4: Parts list for hydraulic circuit diagram Fig. 01-3

Bosch Rexroth AG
01
Device arrangement
Fig. 01-5: Device arrangement for parts list Fig. 01-4 and hydraulic circuit diagram Fig. 01-2
Notes

7
01
Safety instructions
The operating instructions and accident prevention regulations must be observed.
Danger due do flying component parts.
Do not disassemble components under pressure.
Risk from pressurized oil.
Risk of injury from leaking oil and oil jet.
Connect the return line T properly.
Only assemble/disassemble circuits at zero pressure.
Pressure release:
Lower the load
1)
3-way ball valve in rest position (vertical)
2)
Switch the directional valve several times
3)
Unload accumulator
4)
Control by means of pressure gauge: 0 bar in P, A, B
5)
If the tank port is closed, the control block may burst.
The tank channel is only approved for 30 bar.
If the tank port at the control block is closed, 60 bar and - with the pressure
intensification of the cylinder - 100 bar may result in the T channel!
The correct connection of the return lines T is particularly important!
Control block T must be connected at the connection block T1 or T2.
The pilot oil return line Y is to be connected at zero pressure, e.g. at the measur-
ing glass. Accumulator T must be connected at the connection block T1 or T2.
After termination of the practice:
Lower the load
1.
Switch the 3-way ball valve in rest position
2.
Switch the directional valve spool through several times in both directions
3.
in order to discharge residual pressures.
Empty the pilot oil accumulator by opening the unloading valve.
4.
Control by means of pressure gauge
5.
Switch off the pump
6.
Warning
Caution
Caution

Bosch Rexroth AG
01
Order execution
Requirements on the control:
The hydraulic circuit is set up so that first of all, no actuator is connected.
The primary pressure is limited by means of a pressure relief valve in the P line and the LS
pressure limitation in the connection block.
For evaluating the system behavior, the flow rate in the P line from the connection block to
the distributor is measured.
Note for trainers:
Using the data sheet RE 64276, the correct connection of the M4-12 control block can
be worked out. Ports T, P, LS and Y must be used.
The pilot pressure ports a, b must be short-circuited. Otherwise, the control spools is
blocked by leakage oil.
With the data sheet, it is also possible to determine the position of the components and
the measuring points.
In the control block, there is no primary pressure valve. This function is performed by an
external pressure relief valve DD1 at the distributor.
The LS-DB is located in the connection block (see operating instructions).
The sealed pressure valves at the unit must not be adjusted.
Set up the circuit. In this connection, proceed according to the following points:
1. Hydraulic control
Work out the circuit diagram and the parts list in order to satisfy the requirements.
Hang in the hydraulic components according to the circuit diagram and establish the hose
connections.
For connecting pressure gauges with DZ1.4 measuring line, pressure hoses DZ 25.1 are
used.
Manually tighten the pressure gauge measuring lines at the relevant measuring port of the
pressure hose.
Check the correct tight connection of the components with the pressure hoses by turning
the hoses.
2. Setting the pressures and measuring the flow rate qP
Before switch-on of the pump, the LS-DB and the primary pressure valve are unloaded.
After pump switch-on and operating position of the 3-way ball valve, only a low pressure
will build up.
First of all, the safety pressure is to be set using the primary pressure valve.
As this pressure is the higher one, the LS-DB must first of all be set to max. by rotating
the set screw to the right stop.
The 1A directional valve is operated. There is no actuator flow as the system is operated
against the closed couplings.
Using the primary pressure valve, the safety pressure is set to p = 65 bar (measuring
point MP).
Note down the flow rate qP with operated directional valve.
Operate the 1A directional valve and unload the LS-DB until an operating pressure p =
40 bar is reached.
Here, note the flow rate qP with operated directional valve, as well.

9
01
3. Determining the power loss
With P (kW) = p (bar) • qP (l/min) / 600, the power loss can be calculated.
Power loss at safety pressure = 0.63 kW (~ 6.5 l/min • 65 / 600)
Power loss at operating pressure = 0.07 kW (~ 1.0 l/min • 40 / 600)
Note for trainers:
The order of the pressure settings is: First the higher safety pressure, then the lower
operating pressure.
At the safety pressure, the entire pump delivery volume flows off via the primary pressure
valve with max. pressure.
A considerable amount of heat is generated.
At the operating pressure, the pressure signal to the pump controller is limited by the LS-
DB and the pump is regulated. In this case, not much heat is generated as there is no
pump delivery.
In practice, this means a reduction in the heat loss and thus a reduction in the fuel con-
sumption if actuators are moved to stop.
In practice, the difference between primary pressure valve and LS-DB is to be at least
20 bar.
Assessment of the work results
a) In which order do you have to set the maximum pressures?
First of all, the higher safety pressure and then the lower operating pressure is set.
Which pressure limitation results in the higher power loss?
b)
The safety pressure limitation results in the higher power loss as the
entire delivery volume flows off with high pressure via the primary pressure valve.
Project/trainer information
In the present project 01, knowledge of the correct pressure setting is developed in a
practical set-up.
In the practical set-up, the following knowledge is to be gained:
Knowledge of the measuring points
•
Order of the pressure setting of safety and operating pressure
•
Determination of the power losses with the different pressure limitations
•

Bosch Rexroth AG
01
Notes

1
RE 09970/03.11 I Project 02: Actuator flow with stroke limitations Bosch Rexroth AG
02
Project 02: Actuator flow with stroke limitations
Project definition
A large rotary drill is operated with a load sensing control for the rotary disk and the cylin-
der feed.
Settings are to be made in the commissioning.
The maximum speed of the rotary disk is to be limited so that the drill works perfectly and
is not overloaded. The max. actuator flows shall be A1 = 4 l/min and B1 = 5 l/min.
Fig. 02-1: Caterpillar crane
Project tasks
The function of the directional valve element with pressure compensator is to be
•
worked out.
Find the location of the set screws.
•
Measuring and setting the actuator flows.
•

2 Project 02: Actuator flow with stroke limitations I RE 09970/03.11
Bosch Rexroth AG
02
Project steps
points located?
• Checks: Are the required values achieved?
Notes

3
02
Circuit diagram hydraulic set-up
Size 4
Measuring glass
Measuring glass

Bosch Rexroth AG
02
05 1 Motor DM8
12 2
DZ1.4
1
Hose line 90° 1000 mm with measur-
ing port
DKO/DKO90x1000 M
2 Hose line 630 mm with measuring port DZ25.3
1 Optical speed sensor (optional) E19

5
02
Device arrangement
Notes

Bosch Rexroth AG
02
Safety instructions
Pressure release:
Lower the load
1)
2)
3)
Unload accumulator
4)
5)
Lower the load
1.
2.
3.
in order to discharge residual pressures
Empty the pilot oil accumulator by opening the unloading valve
4.
5.
Switch off the pump
6.
Order execution
The hydraulic circuit is set up so that the rotary motor is connected to A1, B1.
The primary pressure is limited by means of a pressure relief valve in the P line and the LS
pressure limitation in the connection block.
The flow rate is measured in the P line from the connection block to the control block.
Warning
Caution
Caution

7
02
Note for trainers:
Using the data sheet RE 64276, the correct connection of the M4-12 control block can
be worked out. Ports T, P, LS, Y, A1 and B1 must be used.
The pilot pressure ports a and b must be short-circuited.
With the data sheet, it is also possible to determine the position of the components and
the measuring points.
In the control block, there is no primary pressure valve. This function is performed by an
external pressure relief valve DD1 at the connection block.
The LS-DB is located in the connection block (see operating instructions).
The sealed pressure valves at the unit must not be adjusted.
Using the pressure compensators available in the directional valve element, the pressure
difference is maintained constant using the control spool.
Thus, the flow volume is only controlled by means of the opening cross-section.
The stroke limitations can be used to set the maximum opening cross-section.
It can be worked out by means of the sectional drawing which set screw is to be ad-
justed for the relevant actuator.
connections. For connecting pressure gauges with DZ1.4 measuring line, pressure hoses
DZ 25.1 are used.
Manually tighten the pressure gauge measuring lines at the relevant measuring port of the
pressure hose.
2. Setting the actuator flows and measurement of the flow rate qP
The pressure settings from project 01 are taken over.
After switch-on of the pump, only a pressure = 15 bar will build up measuring point MP1).
This pressure is the so-called standby pressure that is available with de-energized actua-
tors.
The A1 directional valve is operated. There is an actuator flow according to the directional
valve opening. With max. operation, the actuator volume is set to 4 l/min.
Operate the B1 directional valve and set the actuator volume to 5 l/min.
Note for trainers:
By explaining the pressure differential Δp and the pressure compensator, the function of
the directional valve elements and stroke limitations can be made clear.
It is important to see that with the stroke limitations, the maximum actuator flows and
thus the maximum velocities can be set individually.
Assessment of the work results

Bosch Rexroth AG
02
Notes
a) Which actuating elements are used to set the max. actuator flow volume?
Stroke limitations are used to set the max. actuator flow volume.
Why can the max. actuator flow volume be set with the stroke limitations?
b)
The max. actuator flow rate can - because of the constant pressure differential Δp at
the directional valve spools - be set with the stroke limitations.
Which component is used to keep the pressure differential
c) Δp at the directional valve
spools constant?
Pressure compensators keep the pressure differential Δp at the directional valve
spools constant.
Project/trainer information
In the present project 02, knowledge of the setting of maximum flow rates is developed in
a practical set-up.
In the practical set-up, the following knowledge is to be gained:
Knowledge of the measuring points
•
Setting possibilities for the max. actuator flow volume
•

1
RE 09970/03.11 I Project 03: Load pressure compensation Bosch Rexroth AG
03
Project 03: Load pressure compensation
Project definition
A large rotary drill is operated with a load sensing control for the rotary disk and the cylin-
der feed.
Now, the speed of the rotary disk is to be check with different loads.
In case of loading by solid ground, the speed of the rotary disk is to remain constant, if
possible, so that the drilling power is not reduced.
The max. actuator flow for drilling is A1 = 4 l/min.
Fig. 03-1: Mobile excavator
Project tasks
The function of the directional valve element with pressure compensator is to be
•
worked out.
Working out and using the pressure compensator function.
•
Measuring the input pressure and the LS pressure.
•
• ΔpLS.

2 Project 03: Load pressure compensation I RE 09970/03.11
Bosch Rexroth AG
03
Project steps
points located?
• Checks: Is the requested constant speed achieved and complied with?
Notes

3
03
Hydraulic circuit diagram
Size 4
Measuring
glass
Measuring glass
Measuring glass

Bosch Rexroth AG
03
05 1 Motor DM8
06 1 Pressure sequence valve DD3
13 3
DZ1.4
1 Hose line 90° 1000 mm with measur-
ing port
DKO/DKO90x1000 M
2 Hose line 630 mm with measuring port DZ25.3
1 Optical speed sensor (optional) E19

5
03
Device arrangement
Notes

Bosch Rexroth AG
03
Safety instructions
Pressure release:
Lower the load
1)
2)
3)
Unload accumulator
4)
5)
Lower the load
1.
2.
3.
in order to discharge residual pressures
Empty the pilot oil accumulator by opening the unloading valve
4.
5.
Switch off the pump
6.
Order execution
The hydraulic circuit is set up so that the rotary motor is connected to A1, B1.
The primary pressure limitation 65 bar is realized using a pressure relief valve in the P line
and the LS pressure limitation 50 bar in the connection block.
For simulating the load, a pressure sequence valve is installed in the A1 line in front of the
motor.
Warning
Caution
Caution

7
03
Fig. 03-5: Table
Load pressure
MpL
(in bar)
Pressure Mp
(in bar)
Pressure MpLS
(in bar)
Pressure differen-
tial DpLS
(in bar)
Motor speed n
(in min–1)
Motor 1 Motor 2 Motor 1 Motor 2 Motor 1 Motor 2
17 31.2 28.8 17.5 16 14.3 480 466
20 34.5 32.0 20.8 18 14.1 480 466
25 39.4 37.3 25.7 25 14 480 466
30 44.6 42.2 30.9 30 13.9 480 466
35 48 46.0 34.7 35 12 450 430
40 48.9 47.2 35.6 38 8.4 310 330
45 49.5 47.8 36.3 40 4.1 170 143
50 50 0
Note for trainers:
The DD3 pressure sequence valve is installed for load simulation in the A1 line in front
of the motor.
That is why the DD3 pressure sequence valve only opens above the set pressure and
keeps the pressure in the A1 line at the set value. The idle run resistance of the motor is
not influenced.
For the control block function, the pressure in the actuator port A1 is decisive.
The leakage oil connection T of the DD3 pressure sequence valve must be connected at
zero pressure.
connections.
For connecting pressure gauges with DZ1.4 measuring line, pressure hoses DZ 25.1 are
used.
Tighten the pressure gauge measuring lines at the relevant measuring port of the pressure
hose manually.
2. Setting different load pressures, measurement of speed and pressures Mp,
MpLS, MpL
After switch-on of the pump, only a pressure = 15 bar will build up.
This pressure is the so-called standby pressure that is available with de-energized actuators.
The DD3 pressure sequence valve is completely unloaded.
The A1 directional valve is fully operated (pull the lever).
The motor rotates with pressures according to the load.
The load pressure is increased in 5 bar steps up to 50 bar.
Enter the pressures Mp, MpLS, the pressure differential ΔpLS and the motor speed n into
the table.
Measure the load pressure in front of the pressure sequence valve and MpL at A of the motor.
Smallest load pressure: 17 bar

Load sensing control 2M4-12.pdf

Load sensing control 2M4-12.pdf

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