How to Inspect and maintain Hydraulic System?

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How to Inspect and maintain Hydraulic System?

Hydraulic transmission is widely used in construction machinery because of its smooth and uniform motion transmission, small size, compact structure, sensitive response, simple operation, easy automation, automatic lubrication, high degree of standardization, and long life of components.

At the same time, there are also some shortcomings, such as high requirements for hydraulic oil, high price of hydraulic components, and difficulty in finding the cause of hydraulic equipment failure.

Therefore, once a failure occurs during use, it is difficult to accurately diagnose. Therefore, when the hydraulic system fails, the maintenance personnel are often at a loss, and often cause deformation and damage of the parts during the maintenance, and cause certain losses to the user.

1. Checking method of hydraulic system failure

  • Direct observation method

In diagnosing hydraulic system failures of construction machinery, the intuitive inspection method is the most convenient and easiest method, which is to check the parts by sniffing, hearing, touching, and seeing to make some simple fault judgments.

The visual inspection method is feasible when the machine is working and not working. Although the visual inspection method is relatively simple, it is a very feasible method. As long as accumulated experience for a long time, the inspection process will be more handy.

  • Operation adjustment inspection method

The operation adjustment inspection method refers to operations taken under load and no-load operation. By comparing with the previous work conditions, faults can be found faster and more accurately.

In the inspection process, it is first necessary to perform an operation under no-load conditions, and ensure the normal operation of all hydraulic systems, so that abnormal places are exposed. Then operate under load conditions.

The operation method must be fully combined with the adjustment method in the process of checking the fault. The adjustment process refers to adjusting the adjustable parts such as the stroke, flow and pressure of the hydraulic system and the fault-related components to find the cause of the fault.

  • Contrast replacement inspection method

If there is no test instrument when checking the hydraulic system failure, then the contrast replacement inspection method is a very effective method.

 However, when the comparative replacement inspection method is used to check the failure of the hydraulic system, the operation process is very complicated due to inconvenient dis-assembly, many components, and structural limitations.

Compared with the one-way valve, overflow valve, balance valve and other easy-to-disassemble, small-volume components, using this method is very convenient. In the process of using the contrast replacement inspection method, you must pay attention to the correct connection, and can not cause damage to other surrounding components, so as to ensure the correctness of the fault judgment.

  • Instrument measurement inspection method

When detecting the failure of the hydraulic system, the instrument measurement inspection method is the most accurate method. The fault judgment is made by measuring the oil temperature, flow, pressure, etc. Among them, measuring pressure is relatively common, and the flow rate can be roughly judged by the execution speed of the component.

Under normal circumstances, select several key points in the entire hydraulic system, measure the pressure of the hydraulic system, and then compare the data on the system diagram to judge the condition of the oil circuit before and after the measured point.

2. Maintenance of hydraulic system

Correct maintenance is the foundation of the reliable operation of the hydraulic system. According to work practice, the maintenance of the hydraulic system of construction machinery should do the following.

  • Hydraulic oil

The hydraulic oil plays the role of transmitting pressure, lubricating, cooling, and sealing. The hydraulic oil should be selected according to the brand specified in the “Instruction Manual”. Under special circumstances, the substitute oil should meet the same performance as the original brand, and hydraulic oils of different brands cannot be mixed. Inappropriate selection of hydraulic oil is the main reason for the early failure of the hydraulic system and the decline in durability.

  • Regular maintenance

At present, some hydraulic systems are equipped with smart devices, but their monitoring range and accuracy have certain limitations. Regular inspection and maintenance of the hydraulic system is still essential. Therefore, the inspection and maintenance of the hydraulic system requires the monitoring of the smart device combined with regular inspections.

  • Prevent the invasion of particulate impurities

Pure hydraulic oil is the life of the hydraulic system. If the hydraulic oil is mixed with solid impurities, it will cause strains on the precision parts, jams, blockage of the oil passage, etc., which may even endanger the safe operation of the hydraulic system.

To prevent the mixing of solid impurities, pay attention to the following points: When refueling, the hydraulic oil must be filtered, and the refueling tools should be clean and tidy. The filter at the filler port of the hydraulic oil tank cannot be removed in order to increase the fueling speed.

  • Prevent the intrusion of fluids such as water and gas。

Excessive water in hydraulic oil will rust the hydraulic components, emulsify the oil, reduce the strength of the lubricating oil film, and accelerate mechanical wear. Therefore, not only to prevent moisture intrusion during maintenance, but also to tighten the lid when the oil storage barrel is not in use, best to put it upside down.

3. Conclusion

For the pollution and leakage of the hydraulic system of construction machinery, analyze and explore the root causes of the failure, understand the factors that cause the failure, and recognize the hazards. Pay attention to use problems and preventive measures, correctly select hydraulic oil according to the basic requirements, and use and maintain it reasonably, which can effectively improve the working performance, efficiency, economy, reliability and service life of hydraulic equipment.

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How to analysis on the generation and elimination of vibration in fluid hydraulic system?

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How to analysis on the generation and elimination of vibration in fluid hydraulic system?

Vibration is a phenomenon that often occurs in the working of hydraulic systems. It mainly comes from two aspects: the vibration generated by the movement of the mechanical system and generated during the working process of the fluid.

Most of the vibrations are very harmful to the hydraulic system, of course except for the hydraulic equipment that uses the principle of vibration.

Vibration directly affects the performance of the main engine and the hydraulic system, causing damage to the hydraulic components, accessories and pipelines. Then thereby it will shorten the system service life.

1. Causes of fluid vibration

  • Vibration of hydraulic pump

The flow pulsation of a hydraulic pump is an inherent characteristic of the pump. During the process of sucking and pressing oil, the pressure and flow periodically change will form a pressure pulse.

This pulsation will inevitably cause pressure pulsation in the outlet pipe of the hydraulic pump and spread to the entire system, produce fluid vibration. In addition, the pressure shock in the trapped area of the hydraulic pump, the back flow of the plunger pump, and the inability of the variable pump to reduce the oil delivery in time when the oil pressure rises, all will cause hydraulic vibration.

  • Vibration caused by bubbles

The oil is generally mixed with about 2% to 5% of air, and the mixed air is suspended in the hydraulic oil in the form of bubbles with a diameter of 0.05 to 0.5 mm.

When the partial pressure of the oil mixed with air drops to the air separation pressure, the dissolved air in the oil will separate and precipitate, forming a large number of bubbles (this phenomenon is called cavitation).

When the oil with a large number of bubbles flows again to a higher pressure at high places, the bubbles are instantly crushed to form local high pressures, causing large pressure fluctuations and causing the system to vibrate.

  • Vibration caused by hydraulic valve switching

In the hydraulic system, when the load inertia is large, if the directional control valve is suddenly closed or opened, the flow rate of the liquid flowing in the pipeline will change suddenly. At this moment, the conversion of the kinetic energy of the liquid will cause pressure shock and cause vibration.

  • Forward rush phenomenon and vibration caused by impact load

When the load change causes the hydraulic actuator to suddenly change from the working state to the unloaded state, due to the inertia of the system, a forward thrust will occur, causing hydraulic shock and vibration.  When the hydraulic actuator is suddenly loaded from the no-load state, due to the shock load causes the liquid pressure to rise suddenly, causing pressure shock and vibration.

2. Measures to eliminate fluid vibration

  1. Reduce the influence of air bubbles
  • Reasonable selection of hydraulic components will help reduce the influence of air bubbles on the system

When selecting an oil suction filter, you can choose an out-of-box self-sealing oil suction filter with a signaling device, such as the TF series out-of-box self-sealing oil suction filter. When the filter element is blocked by contaminants, the vacuum degree of the oil outlet is 0.018, then the transmitter will send out an alarm signal to remind the operator to replace the filter element in time to avoid clogging of the filter element. Or it will result in poor oil suction of the oil pump and partial vacuum at the oil inlet and air suction.

  • Reasonably design the structure of hydraulic components to help reduce the influence of air bubbles in the system

Set up pressure measuring joints with exhaust devices at each high point of the hydraulic pipeline, and regularly discharge the gas mixed into the pipeline through the exhaust device of the pressure measuring joints.

When designing the oil tank, set the oil filter and the oil suction filter respectively arranged at both ends of the oil tank to increase the stroke of the oil flowing in the oil tank, so that the oil has as much time as possible to precipitate bubbles during the bypass process.

The pipeline connection is well sealed , Choose a combined sealing gasket with better sealing performance at the junction of the pipe joint and the integrated block to avoid air infiltration.

2. Reduce the impact of hydraulic valves

The reversing valve and the overflow valve in the hydraulic valve are easy to cause fluid impact, and then cause vibration. So this point should be considered when selecting the model.

Selecting the directional valve, when the pressure is high and the flow is large, choose the elector-hydraulic directional valve with better commutation stability. When selecting the directional valve’s neutral function, if the load inertia is large, you can choose Y type Function to ensure that there is still a certain buffer effect after the valve is closed. If the hydraulic motor of the large inertia system is not allowed to continue to rotate after the reversing valve being closed, you can choose the O-type or M-type function.

And before the reversing valve is closed, it is best to first unload the hydraulic pump and close the reversing valve after a certain delay. If select the overflow valve, when the pressure is high and the flow is large, use the pilot-operated overflow valve.

3. Appropriate dynamic compensation

If an overload supplement valve and a back pressure valve are installed in the system, the dynamic performance of the system will be greatly improved and hydraulic shock will be reduced.

In addition, setting a back pressure valve can also increase the minimum working pressure of the system, avoid the generation of bubbles. And at the same time it will slow down the front-shooting phenomenon caused by changes in working conditions, thereby reducing system vibration.

4. Other measures

In order to reduce pipeline vibration, when designing hydraulic pipelines, pipe clamps can be installed according to the design specifications and sharp turns of the pipeline should be avoided as much as possible.

Accumulators should be installed at the inlet and outlet of hydraulic actuators to relieve hydraulic shock.

3. Conclusion

Vibration is an inseparable physical phenomenon of the hydraulic system. Correctly analyzing the causes of vibration and taking reasonable and effective control measures are important to improve the efficiency of the system and extend the life of the system.

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Is test point adaptor necessary for hydraulic system?

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Is test point adaptor necessary for hydraulic system?

The hydraulic system is very complicated.

During the flow of hydraulic oil, the erratic flow direction and flow rate of the liquid are difficult to predict, especially for the long distance.

For such a complex hydraulic system, the system is difficult to debug and maintenance is inconvenient.

Therefore, this feature should be fully considered in the design process, and various possible means should be used as much as possible to improve and enhance the performance of the system.

The application of pressure test point in the hydraulic system is helpful to the debugging of the system. And it can improve the working performance of the system.

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1. The application of pressure test point is helpful for system fault diagnosis

The hydraulic system inevitably has various faults during the working process, and the reasons for the faults are often very complicated. The abnormal working of the hydraulic motor is one of these complicated faults.

The reason for the abnormal working operation of the hydraulic motor is complicated. It can be caused by the blockage of the hydraulic or hydraulic pipeline, or it may be caused by the failure of the load or the hydraulic motor itself.

Once a failure occurs, quickly identifying the cause of the failure is the key to troubleshooting.

Install a pressure test point at the oil inlet of the hydraulic motor, it will help judge the possible cause by testing the pressure of the oil inlet of the hydraulic motor.

It will be very beneficial to find out the cause of the fault and even quickly eliminate the fault.

2. The application of pressure test point is helpful to the adjustment of system pressure.

 In the conventional design, the oil pump outlet of the hydraulic system is equipped with a pressure gauge.

The pressure gauge is not only a measuring tool for adjusting the maximum working pressure of the oil pump outlet, but also a monitoring tool for the working pressure of the hydraulic system.

 Due to the special characteristics of the hydraulic pipeline system such as long oil flow distance, liquid flow direction and flow rate change in the middle, the actual working pressure of the hydraulic motor and the outlet pressure of the oil pump may be far apart.

Through the oil pump outlet pressure gauge it is difficult to debug the actual working pressure of the hydraulic motor and the detection of the working pressure of the hydraulic motor, so the pressure adjustment when the hydraulic motor is working becomes very difficult.

And at the same time, it is impossible to make the hydraulic motor work under the appropriate pressure, which will inevitably affect the working performance of the hydraulic system  and the working state of the hydraulic motor.

 If a pressure gauge is installed directly at the oil inlet of the hydraulic motor, although the working pressure of the hydraulic motor can be measured, it will increase the cost of the hydraulic system. Moreover, the choice of the installation position of the pressure gauge, as well as the working environment and service life are all difficult to guarantee. If a pressure test point is installed at the oil inlet of a hydraulic motor, the situation is different.

Since the pressure test point is very close to the hydraulic motor, the pressure measured basically reflects the working pressure of the hydraulic motor, which will help the accurate adjustment of the working pressure of the hydraulic motor. At the same time, the cost of the pressure test point is relatively low, the installation location is easy to choose, it is not restricted by the working environment, and the service life is long.It can completely avoid the various problems of installing the pressure gauge at the oil inlet of the hydraulic motor.

3. The application of pressure test point helps to improve the working performance of the system

Hydraulic shock is inevitable in the process of hydraulic work, and hydraulic shock is very harmful to the normal operation of the hydraulic system. Avoiding or reducing hydraulic shock as much as possible is a problem that must be considered in the hydraulic system design process.

There are many reasons for the hydraulic shock, including the sudden change of the liquid flow direction and the mixing of air bubbles in the hydraulic oil. Then we can fix the pipe by using the hydraulic pipe clamp to avoid severe vibration, and set the air bubble filter metal mesh in the oil tank. And by extending the distance of the liquid flowing in the tank to make the bubbles gradually seep out, try to avoid the sudden change of the liquid flow direction.

Therefore, it is a good choice to install a pressure test point in the hydraulic pipeline. The pressure test point can be used to release the gas gathered in the higher part of the hydraulic pipeline, so as to compensate for the low rate of bubble leakage in the oil tank and reduce hydraulic shock. It is very beneficial to improve the working performance of the system.

In summary, the proper application of pressure test point in hydraulic systems generally has more advantages than disadvantages. It is very useful for fault diagnosis, debugging and performance improvement of hydraulic systems.

What is the function of test point in hydraulic system?

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What is the function of test point in hydraulic system?

In order to simplify machinery structure design, the driving systems of modern machines commonly are driven by full hydraulic systems. 

The features of full hydraulic system include reasonable overall layout, simple structure design, convenient system operation, reliable quality, strong driving power and convenient maintenance and commission.

It becomes more and more popular among users.

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In order to understand the working situations of full hydraulic system comprehensively, the pressure testing points are set in the design of full hydraulic system, and pressure taps are equipped as well in the pressure testing points to measure whether the pressure in the oil way is within normal range or not, so as that the pressure can be measured quickly for troubleshooting.    

Ikin test point in hydraulic valve

I. The working principle and application of pressure test point

1. There is a self-sealing valve in the pressure test point. Due to the function of spring, it would be closed when used separately.

And it would be opened when it is connected with the measuring hose tube or pressure test point with same thimble to take samples and system pressure testing in the high-pressure or low-pressure fluid system.

The working pressure can reach 63Mpa, and pressure of BP can reach 250Mpa.

the video shows how Ikin hydraulic test point works

2. The pressure test point is mainly used in the full hydraulic tubing system for pressure supervision detection, gas discharging, samples taking in the high-pressure and low-pressure systems.

It is widely used in the engineering machinery, agricultural machinery, hydraulic system, testing equipment and so on.

For example, the hydraulic system and operating of hydraulic excavator are complicated, but how to judge hydraulic failures?

Shown as the below picture, pressure test point is needed now to measure the hydraulic pressure of testing point so as to find the root of the problem.


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The pressure tap can bear pressure testing in the hydraulic system, which is critical significant for stable hydraulic equipment and reliable operation.

Therefore, pressure test point is widely used as standard configuration in current hydraulic systems.

II. The necessity of setting Hydraulic testings

The whole moving system driven by hydraulic system is integrated by hydraulic motor, hydraulic action component, hydraulic valve, oil pipes and others. It is very complicated.

The pipe line from oil pump to hydraulic action components is long, as well as the hydraulic flowing distance. It is hard to predict press loss as fluid flowing direction and flowing speed changes.


IKIN FLUID pressure test point

It is difficult for system commission and inconvenient for maintenance.

As a result, the features of full hydraulic system should be taken into full consideration in the design. Pressure testing points should be set and hydraulic testing should be equipped.

Meanwhile, the cost of hydraulic testing is low, installation location is flexible, and it is not limited by working environment with long usage life.

It is benefit for hydraulic system commission and working performance of hydraulic system could be improved.

III. Convenient for failures diagnosis in full hydraulic system

The full hydraulic system is complicated, and number of hydraulic motors and integrated valve blocks are many, leading the probability of failures is high. Once failures happen, finding the reasons of failures quickly is the key in troubleshooting.

Installing hydraulic testing in full hydraulic system can analyze the reasons that may happen through pressure testing in all pressure points.

With the help of hydraulic testing to analyze potential reasons for failures in full hydraulic system, it is very good at troubleshooting and finding out reasons for failures.

IKIN hydraulic pressure test point

IV. Improve the working performance of full hydraulic system​

The number of pumps and motors in full hydraulic system is many, and flow capacity of oil is high. Due to the limitation of machinery structure, the flowing distance of hydraulic oil in the oil box is short, bubble exudation rate is low, and huge amounts of bubbles would be brought into pipeline again.

Hydraulic test point installed in hydraulic pipeline can be used to release gas in higher parts that are gathered in the hydraulic pipeline so as to make compensation for the shortage of low bubble exudation, which is very beneficial for decreasing hydraulic impacts and improving working performance of system.

IKIN FLUID pressure test coupling

V. Conclusion

The number of hydraulic components and action parts is many in the full hydraulic system, and system is complicated.

Machinery structure, working environment, special demands and various issues that may happen should be taken into full account when design full hydraulic system equipment.

It is very necessary to adopt various methods comprehensively to improve working performance and maintainability.

Generally speaking, in the improving the reliability of quality, the advantages of proper adapting hydraulic testing in full hydraulic system equipment are more than disadvantages, which are also very beneficial for commission and performance improvement in full hydraulic system.

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What is the common leakage problems and possible causes of Hydraulic Testings?

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What is the common leakage problems and possible causes of Hydraulic Testings?

As an important tool for pressure testing and sampling in hydraulic systems, hydraulic test point are widely used.

However, establishing a reliable and leak-free connection should be the primary goal of any hydraulic system.

There are many different kinds of hydraulic testings on the market can be selected. No matter which type , it will bring inconvenience and trouble to the entire system when leaked.

Common leakage problems and possible causes of hydraulic testings:

1. When the oil leaks from the inlet end, possible reasons for this region leaks as follows:

IKIN FLUID hydraulic test point
①O-ring/sealing ring is damaged or missing (For O-ring joint / seal ring)

The unreasonable design of the sealing ring and the sealing groove will cause the compression of the sealing ring to be too large or too small; if it is frequently disassembled, the surface of the sealing ring may be worn, slag and not pressed tightly.

When the use time is too long to exceed the shelf life, the ring loses its sealing, elasticity, deformation and cracks, etc., so it is easy to leak.

② The size of the connecting thread of the joint body is poor

The connecting thread of hydraulic testings is selected according to the thread of the oil port end.

The external thread connection length of hydraulic testings should be less than the full thread depth of the internal thread of the oil port end. Otherwise, the thread of the column end will not be screwed to the bottom, resulting in leakage of the threaded end.

③ The oil port end is damaged

Scratches on the sealing surface of the O-ring at the port end will prevent the O-ring from effectively sealing, resulting in leakage; the edge of the O-ring sealing surface is too sharp or burrs, and it is easy to cut the O-ring during installation and cause leakage;

④ Improper torque / improper assembly

After torque assembly, make sure that the end face of the joint seal is in full contact with the end face of the oil port. If there is a slight gap, the O-ring is likely to be squeezed out during the system’s long-term pressurization process, resulting in leakage.

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2. Leakage in the center of the spool. The possible causes of leakage in this area are as follows:

IKIN FLUID hydraulic test
① Excessive pressure

According to the international standard ISO 15171-2, the maximum working pressure of hydraulic testings is 63Mpa (630bar). If the system pressure is too high (the maximum pressure exceeds the limit), the valve core will be damaged by a huge impact, which will cause hydraulic testings to leak.

② Damage of internal seal

When impurities enter the hydraulic system and the pressure is tested, these impurities will damage the internal seals of hydraulic testings, and will also affect the service life of the entire hydraulic system.

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3. Leakage caused by cracks. The possible reasons for leakage in this area are as follows:

IKIN FLUID hydraulic test
① The wall thickness is too thin

When the design wall thickness of some parts of the hydraulic test point joint is too thin, and there is stress concentration, the thin-walled part will be broken or cracks will cause leakage.

② Inferior quality materials

Choosing low-quality materials may cause small cracks in the joint body, but these cracks will be difficult to find after electroplating.

Therefore, hydraulic testings body will expand and crack under the constant pressure of the system, resulting in leakage.


The above is a summary of hydraulic testings in the hydraulic system application practice, and several reasons are prone to leakage.

In practice. The possible causes of leakage should be analyzed and found in combination with the actual situation, and the problem should be quickly eliminated by searching for it in an orderly manner.


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