Properties of hydraulic system in diagnostic area – mini review

. Hydraulic systems can be found everywhere, transmitting very large forces very quickly. Like all systems, they wear out and suffer damage. It is therefore important to be able to diagnose the systems to know whether their behaviour is correct or not. This requires different tools, such as digital simulation and the implementation of procedures. Thanks to these, it is possible to know the theoretical behaviour of the system. Our brief study focuses on the implementation of procedures in order to be able to set up a whole battery of diagnostics.


Introduction
Hydraulic systems are used in many fields, including industry, the automotive and construction and public works, to name but a few of the best-Known.First of all, what is a hydraulic system?It's a system for transmitting movement using an incompressible fluid.It is a closed system consisting of a reservoir, a filter, a pump to create pressure within the system, a relief valve to protect the system against pressure variations, one or more distributors and receivers such as cylinders and motors.Below is a simple diagram of a hydraulic system with a cylinder.
What makes hydraulic systems so attractive?It's the fact that they can develop enormous force and power while remaining compact.Hoses make it much easier to transmit and transport this energy.The most obvious example is the evolution of excavators, the first of which were cable-operated, but after the Second World War the hydraulic excavator made its appearance.It was cheaper to manufacture, its power could be used in all movements, and the interchangeability of tools were all factors that made the hydraulic shovel much better.
However, hydraulic systems have several disadvantages.Firstly, these systems tend to leak.This is dangerous because when in contact with electrical elements, heat or sparks, the oil can ignite and cause a great deal of damage to the system.Oil can also be highly corrosive and very messy, so it is vital to protect yourself properly when handling it.Another negative aspect is that oil is very sensitive to changes in temperature and humidity, so it is essential to ensure that the system is watertight and temperature-controlled so that system performance is not affected.Temperature and humidity are the two biggest factors in premature wear of a hydraulic system.Humidity generates corrosion, which will then detach and circulate throughout the system, despite the presence of filters.The corrosion will then damage the hoses, but also the mechanical parts such as the pumps and the directional spool valve, damaging the joints and scratching the metal parts.As far as temperature is concerned, if it is too low, performance will be limited and the system will have to be overexploited to perform as well as a system at normal temperature.This will tend to cause premature wear, although this is not the worst problem.A high temperature will change the properties of the oil and degrade it, causing a snowball effect and deteriorating the rest of the system, particularly the hoses and rubbers.But how can you tell if the system is damaged?Apart from leaks, there is no way of knowing whether the system is in good condition or not.As the system is closed, it is impossible to know whether it is behaving correctly or not.Someone who is used to working with the equipment may have become accustomed to this drop in performance without noticing anything.That's why diagnostics are important.In fact, thanks to their documentation, manufacturers can tell us whether the system is behaving correctly.
How do they do this?First they create simulations using software such as AMESIM, then they test them under real conditions to corroborate the results obtained.If no documentation exists, simulation remains the only tool for obtaining reliable data on the theoretical behaviour of the system.However, these are very expensive, which is why only manufacturers use them.On the other hand, it is essential to follow the maintenance instructions, and even to carry them out at tighter intervals.During this maintenance, an indepth inspection of the system will reveal any damage, but will also allow tests to be carried out to ensure that the system is behaving correctly.These tests are an integral part of the diagnostics, just like the visual inspection during maintenance.Without them, the life of hydraulic systems is reduced and breakdowns become very frequent.A system that breaks down too often is a bad system, and will be detrimental to the company that developed it.All these different factors make diagnostics and the development of diagnostics necessary for hydraulic systems.

Study of Hydraulic system damage
Hydraulic systems, while efficient and powerful, are susceptible to various forms of damage.These systems rely on pressurized fluid to transmit power, and as a result, they can be affected by factors such as Corrosion, Cavitation, leaks, Scoring or Scratching, and overheating.Understanding these potential issues is crucial in maintaining the efficiency and longevity of hydraulic systems.Here are some common types of damage effects on the Hydraulic system [14,15,16]: • Scoring or Scratching: Cause: Foreign particles or contaminants in the hydraulic fluid can lead to scoring or scratching on the piston surface.Effect: Reduced sealing efficiency, increased friction, and potential leakage.• Cavitation: Cause: Cavitation occurs when there are rapid changes in fluid pressure, leading to the formation and collapse of vapor bubbles on the piston surface.
Effect: Pitting and erosion on the piston, reduced efficiency, and potential damage to other system components.• Erosion: Cause: High-velocity fluid flow can cause erosion of the piston surface over time.Effect: Material loss, decreased piston diameter, and compromised sealing.• Misalignment: Cause: Incorrect installation or manufacturing defects can result in misalignment of the piston within the cylinder.Effect: Uneven wear, increased friction, and potential damage to the cylinder and seals.• Overheating: Cause: Operating the hydraulic system at temperatures beyond the recommended range can lead to thermal damage.Effect: Reduced material strength, increased wear, and potential distortion of the piston.
• Overloading: Cause: Excessive pressure or force applied to the piston beyond its designed capacity.Effect: Piston rod deformation, cracking, or complete failure.

AMESim in Hydraulic Systems
Hydraulic systems are intricate networks of interconnected components that rely on a specialized fluid to transmit energy and power across a wide range of applications.While numerous software programs can effectively simulate the operation of hydraulic systems, AMESIM stands out as a powerful tool for designing and analysing these complex systems.AMESIM is a software for Multiphysics simulation that is useful for analysing hydraulic system performance.Numerous aspects of the program allow for the analysis of fluid flow, forces, and heat in hydraulic systems.
AMESIM Hydraulic System Features AMESIM has numerous capabilities that are useful for analysing hydraulic system performance, such as: • Tools for 3D design: Pumps, valves, and motors are examples of hydraulic components that can be modelled in three dimensions using these techniques.• The software can be used to analyse the performance of a new hydraulic pump.Engineers can use the software to model the pump in three dimensions and then simulate its real-world operation.These tests can improve the pump's performance as well as its safety.• The software can be used to analyse the performance of a new hydraulic system.
Engineers can use the software to model a system in three dimensions and then simulate how it would function in the real world.These tests can improve the safety and performance of the system.• The software can be used to investigate the hydraulic system failure.Along with the software, engineers can model the system in three dimensions and then simulate a real-world failure of the system.These tests can assist in determining the root causes of failure and helping to prevent it from occurring again.

Presentation of The System
The hydraulic system with two actuators is activated by using manually operated slider hydraulic distributors (lever, knob) and an electrically controlled slider hydraulic distributor.Before starting the machine, properly connect the power supply to the socket so that the ground is on the left side (the plug is marked with the "L" symbol).The device is controlled by a controller, shown in Fig. 9.

Hydraulic System Controller
The controller is equipped with a main switch that turns on the device.In the upper left corner is a safety switch, which is also the machine's switch.To turn off the device, turn off the hydraulic drive and press the safety switch.After a while, the machine will turn off.
Below the power system, there is a hydraulic pump speed management panel (frequency converter).It consists of a display that displays the set frequency in kHz, a knob for setting the speed, and two buttons: green "Run" and red "Stop/Rst".After starting the device, the pressure in the system is established.The working machine can only be operated when the direct flow valve is in the vertical position -liquid is supplied to the manifolds.Otherwise, the liquid will be pumped directly back into the tank.The stand is also equipped with a nitrogen hydraulic accumulator.All you need to do is set the fluid flow levers appropriately in such a way as to cut off the oil flow from the distributors and simultaneously regulate the flow through the accumulator.The liquid tank is equipped with a thermometer controlling the temperature of the working liquid of the hydraulic system and a liquid level indicator.To turn on your device: 1. Pull out the fuse (safety switch).2. Press the main switch button.3. Set the speed.4. Set the motor switch (L/R). 5. Press the green "Run" button of the frequency converter.6. Pressure accumulation in the system begins.

To turn off your device:
1. Press the red button of the frequency converter "Stop/Rst".2. Set the engine switch to position "0".3. Dissipate the accumulated pressure energy (preferably using an electric distributor set the distributor switch to position "1").4. Once the pressure has dissipated, return the electric distributor switch to w position "0". 5. Press the main (safety) switch.6.After turning off the controller, disconnect the plug from the socket.

Methodology of assessment impact diagnostic area in hydraulic system properties
To establish a baseline for evaluating the performance of hydraulic systems, it is crucial to understand their behaviour under normal operating conditions.While the procedure employed is not without its limitations, it provides a valuable reference point for assessing the performance of similar systems.The aim of our procedure here is to find out how our system behaves in normal use.This study will serve as a reference, enabling similar systems to be compared to see whether their behavior is correct or not.Please note, however, that our procedure is not perfect: the system leaked and we had to put the oil back in the tank after a few minutes.This does not allow for optimal conditions and repeatability.The temperature also fluctuated slightly but always remained between 18°C and 22°C.Nevertheless, this method is sufficiently accurate to give an idea of the system's normal behavior.Our procedure consisted of three different tests.
The first was to put as much weight on the left as on the right of the machine.Unfortunately, we didn't have the same distribution on each side.We had 25.9 kg on the left and 24.9kg on the right.We then timed the time it took for the piston to make a return trip, increasing the speed of rotation of the electric motor each time while taking the pressures indicated by the pressure gauge.
The second and third tests followed the same procedure.The difference was that all the weights were placed on the right and left sides respectively representing 60,6 kg.In addition, the maximum rotation speed was reduced to minimize the risk of the weights falling off.When the speed became too high, the weights descended so quickly that they tended to fall.

Result from the First Test (25,9kg left 24,9kg right):
On this graph we can see that the return stroke of the piston becomes faster as the engine speed increases.However, this gain becomes less significant when the speed is very high.
Here we can see that static pressure increases with motor speed.As the pump rotates faster, the flow rate and pressure also increase.
Finally, the last graph shows that as the static pressure in the system increases, the return stroke of the piston becomes faster and faster.

Result from the second test (60,6kg right):
Result from the third test (60,6kg left): We can see in all three cases that the return stroke time of the piston seems to behave like an inverse square root function and that the static pressure in all three cases is broadly similar.This is normal insofar as we are not changing the internal characteristics of the mechanism.The areas where the change is most obvious are in the return stroke times.When there is little rotation speed, test 1 will be faster than the others.At 10 rotations per second, test 2 will be faster, while test 3 and test 1 will be similar.We tried to study with dynamic pressure.However, it was very imprecise and we didn't have the time to read it and find out whether it was stable or not.The system didn't have time to balance itself during the return stroke time.Furthermore, having only 4 points for cases 2 and 3 is not extremely precise, but they do corroborate the analyses of the first test.
Using this data, we can compare the times of simple piston models as a function of their load.What's more, if by varying the speed on a similar model you obtain radically different results and trends, you can conclude that your mechanism is malfunctioning.This procedure serves as a starting point for a more complete diagnosis.

Conclusion
In this Mini-review we have seen that hydraulic systems are not immune to wear and tear and that it is extremely important to take care of them.Many factors can damage systems, such as humidity and temperature.To design a hydraulic system, companies use simulation and design software.This software gives theoretical values for the correct operation of the system.However, nothing can replace real-life conditions.This is why a battery of tests and procedures is put in place to test the mechanism and compare the digital model with reality.
In our case, we only carried out the tests and procedures in order to study the behaviour of our mechanism, which was considered to be new.We were able to draw up data and trends for comparison with other systems of this type.Admittedly, our study is only a first step in the implementation of diagnostics, but it is nonetheless essential and helps to create this connection between hydraulic systems and the implementation of diagnostics.

Fig. 4 .
Fig. 4. Example of Erosion [11].•Corrosion:Cause: Exposure to corrosive fluids or environmental conditions can lead to corrosion on the piston surface.Effect: Weakening of the piston material, reduced efficiency, and potential fluid contamination.

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Dynamic simulation tools: These tools are useful for researching hydraulic system fluid flow.• Tools for thermal simulation: These tools are useful for researching how heat affects hydraulic systems.• Structural simulation tools: These tools are useful for researching how forces affect hydraulic parts.AMESIM Application in Hydraulic Systems.It can be used to research many different hydraulic system topics, such as: • Pump performance: The hydraulic pumps efficiency, pressure, and flow rate may all be studied using the program.• Hydraulic valve performance: The software can be used to examine the effectiveness and reaction time of hydraulic valves.• Motor performance: The software can be used to research the torque and speed of hydraulic motors.• System efficiency: By analysing the quantity of energy lost in the system, hydraulic systems, efficiency may be studied using the program.System stability, vibration, and system failure probability can be studied using the software for hydraulic systems.Examples of AMESIM-Used Hydraulic Systems.Here are a few examples of how AMESIM is used in hydraulic systems:

Fig. 13 .
Fig. 13.Tank with liquid level and temperature indicators [1].The working fluid temperature is controlled using the working fluid heating regulator installed at the top of the station.It indicates the current temperature in the hydraulic pump.