what are the types of Hydraulic hose fittings and failure analysis?

Hydraulic Hose Fitting with Banjo fitting manufacturer in China

what are the types of Hydraulic hose assembly and fittings and failure analysis?

With the rapid development of China’s construction machinery, the reliability of hydraulic hose assemblies has become one of the most concerned issues in the industry.

The hydraulic hose assembly is a basic element in the hydraulic transmission system. The quality of the hose assembly directly affects the performance of the hydraulic system and the main engine. Part of the failure of the hose assembly comes from the structure of the joint core.

The hose connector core is mainly divided into two parts, one is the connection structure, mostly based on SAE standards, ISO standards and KES standards; The other part is the structure of the crimping part (tail structure), which is matched with the outer jacket and the inner and outer rubber layers of the hose to form a reliable crimping deformation to meet the performance of the hose assembly.

If the structure of the joint core crimping part is unreasonable in the design of different types of hoses, product quality problems will occur to a large extent.

Therefore, the types of (designed) joint cores selected for hoses in different working environments are also different, and a reasonable design can avoid or reduce the occurrence of failures.

1. Types and characteristics of hose fittings

Throughout the entire hose assembly industry, there are mainly two types of reliable connections between hose joints and hoses: full withhold hose joints and detachable hose joints.

The full crimping joint is a process in which the eight-part crimping module of the crimping machine uniformly squeezes the hose joint to a certain extent after assembling the joint core, hose and outer jacket, so that the hose joint and the hose become a whole.

The detachable hose connector compresses the hose through the connector core with the outer cone and the connector core, so that the hose is close to the inner cone of the connector sleeve, forming a connection with a greater binding force.

1.1 Hose crimping form and characteristics​

The type of withholding of the hose mainly depends on the type of hose (or the size of the inner and outer rubber) and the pressure environment of the hose assembly.

It is mainly divided into three categories: non-peeling rubber crimping, peeling outer rubber crimping, and inner and outer rubber peeling crimping.

The characteristics of each type are:

(1) Non-peeling and crimping: The inner and outer rubber of the hose does not need to be stripped, and the product can be completed by crimping after the hose is installed. The processing technology is simple.

This type of crimping is often used for steel wire braided hoses with relatively thin outer rubber layers such as GB/T3683, EN853 and SAE standards.

(2) Stripping and crimping: It is necessary to strip off the outer rubber layer of the hose to a certain length (the outer rubber layer is thicker), which is used to better make the steel wire reinforcement layer contact with the tooth groove of the jacket.

When the jacket shrinks and deforms under external force, it will firmly buckle the steel wire, thereby preventing the joint from pulling out when subjected to high pressure impact.

This type of crimping is mainly applicable to steel wire wound hoses such as GB/T10544, EN856, and SAE standards.

(3) Internal and external rubber stripping and crimping: the inner and outer rubber layers need to be stripped to a certain length (the thickness of the inner and outer rubber), the steel wire layer and the inner rubber layer are extruded into a wave shape, generally suitable for GB/T10544, EN856-R13, R15, etc. Specifications (32 or more including 32) ultra-high pressure steel wire spiral hose.

1.2. Withholding type hose connector

Withholding type hose joint is mainly composed of joint core, outer jacket (nut is an optional part) and other parts.

1) Joint core materials, types and characteristics

Commonly materials used for joint cores are 20, 35, and 45 steels. For straight joint cores, 35 and 45 steels are often used, which have strong resistance to deformation. Considering the manufacturability of bending joint cores, 20 or 35 steels are generally used.

With the popularization of hot bending technology, 35 and 45 steels can also be used for elbow joint cores.

The structural characteristics of the joint core are closely related to the hose crimping form, and according to the regularity of the structure, the types of joint cores are roughly divided into: zigzag structure, rectangular structure, internal locking structure, etc.

(1) Sawtooth structure joint core, commonly known as barbed type, is mainly composed of sawtooth grooves, and the angle between the hypotenuse and the axis is generally not more than 20°.

The top of the serration is arc-shaped or flat, and the plane and the short side of the serration are smooth rounded corners (0.2~0.5mm) to prevent damage to the inner rubber layer of the hose during assembly and crimping.

The joint core of this structure has strong sealing and pull-off resistance, and is mainly used for steel wire-wound rubber hoses.

(2)  Rectangular structure joint core: mainly composed of several rectangular grooves, 5~7 groove bodies form a sealing groove, and the groove depth is generally 0.3~0.6mm.

The transition surface between the top of the groove and the bottom of the groove is generally smooth with rounded corners, with a radius of 0.1mm~0.3mm.

Prevent damage to the inner rubber layer of the hose during assembly and crimping. The overall structure is simple, with good sealing performance, but low pull-out resistance. This structure is often used for resin hoses, steel wire braided hoses and other types of hoses.

(3) Internal locking structure joint core, also known as anti-pull-out structure.

This type of structure is specially designed to prevent the hose from being pulled out of the hose joint, and the tightness is ensured by the rectangular structure.

Therefore, the inner locking structure joint core is actually a combination of the anti-pull-out structure and the rectangular structure.

This kind of joint has the characteristics of high reliability and long service life. It is mainly used for ultra-high pressure and large diameter steel wire winding hose and dynamic steel wire winding hose assembly under harsh working conditions.

2) Outer cap material, type and characteristics​

The material of the outer jacket is generally 20 steel, and the good plastic deformation of the material is used to make the outer jacket tooth extruded rubber tube and the joint core sealing fit.

There are also many types of outer caps, mainly for different joint cores, different working environments, different specific working conditions, and different structural forms required.

Usually the inner side of the jacket is made up of some grooves or serrations. There are square grooves, trapezoids, zigzags, etc., which need to be used in conjunction with different types of joint cores.

 The commonly used structure types of outer caps are roughly divided into the following three types:

(1) Wave-shaped tooth groove jacket. The outer surface of the wavy jacket is mainly a smooth cylinder, and the angle between the hypotenuse of the inner tooth and the axis is 25°~45°.

The radial side and the hypotenuse are connected by rounded corners of 0.2~0.5mm, generally composed of 3~5 internal teeth. Mainly suitable for non-peeling medium and low pressure hose assemblies, such as resin tubes and steel wire braided hoses;  It can be used in conjunction with sawtooth structure and rectangular structure joint core, with weak pull-out resistance and simple processing technology.

(2) Trapezoidal tooth groove jacket. The outer surface is a smooth cylinder, and the inner surface is a groove with a certain number of trapezoidal teeth.

The angle between the hypotenuse and the axis is 25°~45°, and each serration is a rectangular groove. The top of the serration is a plane with a width of 1 to 2mm, and the sharp corners are transitioned with a rounded corner of 0.2mm.

It can be used in conjunction with a rectangular structure joint core to form an effective pull-out resistance, suitable for stripping medium and high pressure braided pipes and winding pipes.

(3) Compound alveolar cover. The outer surface is a T-shaped groove corresponding to the internal tooth dislocation, and the inner surface is a groove with a certain number of bilateral trapezoidal teeth.

It is suitable for use with the inner locking structure joint core and is used for ultra-high pressure and big flow rate hose assembly.

With the gradual development of large-scale construction machinery, the hydraulic system is also constantly developing in the direction of high pressure, and the application of this structural form is becoming more and more extensive.

2. Selection of the amount of joint crimping

According to different hose types and joint types, the appropriate crimping amount is also a key factor to ensure that the hose assembly is trouble-free.

The amount of crimping directly affects the sealing performance, pull-off strength and service life.

Generally, when judging the quality of the crimping deformation, see whether the gap between the inner tooth surface of the outer sleeve and the tooth groove of the joint core is filled by the rubber tube.

Only when the deformation is satisfied can the pull-out resistance and sealing performance be guaranteed.

Generally speaking, the crimping amount of inner rubber hose such as nitrile rubber should make the inner rubber layer compression (40%~45% for steel wire braided hose, 50%~55% for four-layer and six-layer steel wire wound hose); The crimping amount of the resin tube and the PTFE hose ensures that the compression amount of the inner rubber layer is 25% to 30%.

In the case of ensuring the seal, the smaller the amount of withholding, the better. Through calculation and verification, a certain amount of withholding is selected.

3. Failure types, causes and solutions

3.1 Types of failure

There are many types of failures of the crimping hose assembly. This article only analyzes the types of failures caused by the hose joint structure and the crimping fit.

There are mainly leakage at the withholding area, hose removal and bubbling at the withholding area.

3.2 Causes of failure

(1) Leakage at the crimping part of the hose assembly is one of the most common failure forms. The main causes are the large deviation of the inner diameter of the hose, the eccentric inner rubber, and the uneven thickness of the outer rubber layer, resulting in uneven crimping; There are internal rubber damage, poor internal rubber elasticity, aging, uneven deformation of the joints, etc. at the connection part of the hose and the joint;

(2) The hose fitting joints are pulled out under pressure impact.

This kind of failure will cause serious accidents, requiring product manufacturers to strictly control the process to avoid this failure.

There are several main reasons for the joint pull-out: the design of the crimping structure is unreasonable; The crimping deformation is small, so that the steel wire reinforcement layer fails to form an anti-pull-out force with the joint; the inner rubber layer is damaged during crimping, etc.

(3) Bubbling at the withholding area also occurs from time to time;This kind of failure problem is mainly caused by excessive crimping, which causes the steel wire layer to break, and the oil penetrates to the surface of the steel wire layer to cause bubbling of the hose;

 3.3 Troubleshooting

(1) When selecting hoses of different brands, fully consider the fit of the hose size and the designed outer sleeve joint core. Achieve reasonable structural design and avoid leakage caused by poor sealing;

(2) In-depth research on the processability of the product should be carried out, and a reasonable amount of withholding should be configured for different joint structures.

Do not overdo it to avoid the phenomenon of breaking the wire layer;

(3) Withholding products must pass various type tests under the support of industry standards;Verify leakage and pull-out faults through pulse, blasting, and other tests;

(4) It is effective to control the raw materials of the hose, and the hose manufacturer uses uniform inspection standards, inspection items and inspection methods.

Enhance the company’s own inspection capabilities to avoid rubber hose processing assemblies with defects such as rubber aging and poor inner rubber elasticity.

4. Conclusion

The article discusses the types of joint cores and outer caps used in the withholding hose assembly.

When the hose crimping has quality problems and the types of failures.

Analyzed the reasons and how to use reasonable crimping configuration and crimping joints, in order to avoid the problem of low hose assembly performance caused by unreasonable hose crimping structure.

Effectively improve and control the reliability of the hose assembly, and also provide strong support for the rapid development of various hydraulic engineering machinery.

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How to maintain and Manage Extrusion Press Hydraulic System

pressure hose fittings manufacturer, China

How to maintain and Manage Extrusion Press Hydraulic System

Large aluminum extrusion presses can be used to produce high-specification aluminum extrusion products such as industrial profiles, rail transit profiles and large radiators.

It can be used in aerospace, rail transit, automobiles, ships, construction, machinery manufacturing, electronic power and other fields. In the working process of large aluminum extrusion press, to ensure the working accuracy and high performance, the premise is to have a certain degree of stability. Once the stability of the extruder fails to meet the production standards, the quality of the products produced will be greatly compromised.  And enterprises will also suffer huge economic losses.

一. Common problems of hydraulic system of large aluminum extrusion press and their solutions

(一) Pipe leakage:

The welding position of the pipe and the flange is most likely to cause pipe leakage. In addition, the pipe flange installation surface and screw position are also extremely likely to cause pipe leakage.

The occurrence of pipe leakage is mainly caused by the loosening of the screw and pipe joints caused by long-term operation. At the same time, after the flange mounting surface seal is aging, the sealing ring will be damaged.

Improper welding caused pores and cracks, and leakage occurred. In addition, the use time was too long, the safety awareness was not strong, and timely maintenance was not carried out, which caused the situation to expand and eventually cause leakage. We can eliminate pipe vibration and improve stability by adding pipe clamps and brackets.

If the welding operation is not standardized, there are pores or cracks, we can polish in the original position, and after the debris is removed, we can weld again.

(二) Oil leakage in the cylinder:

1. The occurrence rate of oil cylinder leakage is relatively high. Due to the long-term working condition, it will inevitably cause a large amount of abrasive particles. At the same time, because the exposed position of the piston rod is exposed to the air for a long time, it is inevitable that there will be a large amount of dust and aluminum powder attached.

In such situations, a dust ring is usually used to scrape out. However, in view of the effect of the dust ring, it is difficult to completely scrape off, so that the piston rod seal is damaged, which in turn causes leakage. Therefore, two treatment methods are usually adopted for oil cylinder leakage: First, clean the oil cylinder and replace the seals; Second, confirm whether the surface layer of the piston rod is worn or not,

2. The axis of the cylinder is not parallel to the guide rail, and the error exceeds the standard range: 0.04-0.08mm/m. In turn, the end cover fixing bolts were loosened and the seal failed. Then we need to maintain parallelism and control the error within the standard range.

3. The seal is broken and the oil leakage occurs due to the back pressure and the pressure setting is too high. In turn, the seal is exposed to excessive pressure and the seal is broken. This requires resetting the hydraulic system pressure and testing the hydraulic control valve components.

4. The seals are severely worn and fail because the hydraulic oil is severely polluted and produces a lot of impurities. When the oil temperature is at a high temperature for a long time, the hydraulic oil is gradually oxidized, resulting in the production of colloidal deposits. When the oil temperature is in a low temperature state for a long time, the elasticity of the seal will be lost. The aging of the seal is caused by the accumulation of a large amount of oil residue.

Then we need to strengthen the management of hydraulic oil and strictly control the intrusion of pollution sources; Confirm the working condition of the cooling system of hydraulic equipment and ensure its normal operation. The most suitable temperature is 30-45℃.

5. When the appropriate seal is not selected for sealing treatment, when selecting the seal. In order to take into account the material, model and roughness of the seal, oil leakage occurs. Therefore, when selecting seals, carefully identify the characteristics of the seals and select the corresponding reasonable seals.

(三) Leakage of control valve components:

Internal leakage is the most common in leakage of control valve components. The root cause of internal leakage is the large accumulation of hydraulic impurities, which in turn blocks the control valve components; In addition, excessive wear of the valve core and improper closing can cause leakage.

Excessive pressure will cause hydraulic clamping of the spool, which will also cause leakage. It is recommended to clean the control valve repeatedly after disassembling, or to polish the control valve components. In order to improve its accuracy and restore it to its original appearance.

(四) Solenoid valve failure: Solenoid valve failure can be divided into the following types:

1. The spool does not move: (1) Electromagnet failure, combined with vibration and magnetic field detection, it can be seen that the spool does not move; (2) The valve core is clamped, the oil changes, and the return spring is faulty. After vibration detection, the valve core stuck failure can be seen;

2. Large pressure loss: (1) The flow is too large and the size is wrong, which can be seen by joint inspection of vibration and magnetic field; (2) The spool does not move in place, and the spool jamming fault can be seen through vibration detection;

3. Magnetic flux leakage: Defects appear on the surface of the electromagnetic coil, which can be seen by magnetic field detection.

4. Shock (vibration): The spool closing speed is too fast, and the screws are loose, which can be seen by vibration detection.

In view of the causes of the above problems, take corresponding measures to solve the problem.

二.  Maintenance and management of hydraulic system of large aluminum extrusion press

(一) Draw up daily maintenance plan

(1) For some equipment exposed to the air for a long time, clean it regularly to keep the exposed parts of the equipment clean and free of impurities;

(2) Keep the operating environment clean and tidy to avoid the intrusion of dust and debris and pollute the hydraulic system;

(3) Carry out patrol inspections at any time where the oil leakage rate is relatively high, and once found, take corresponding measures to solve them immediately;

(4) Standardize the inspection process. Delineate the inspection route and the highest part of the oil spill point. After a certain stage of the inspection work is completed, it shall be handed over with the staff of the next stage, and the work progress of the previous stage shall be explained in detail;

(5) Record the original operating status in detail. Understanding the normal working conditions of the hydraulic system can help to discover and solve problems in time during the inspection process, improve work efficiency, and avoid safety risks.

(二) Develop a regular maintenance and inspection system and schedule a date to calibrate various instruments of the hydraulic system. Ensure that the meter is working properly and has a high degree of accuracy.

At the same time, the hydraulic system should be pressure tested to set a reasonable pressure value to maintain normal temperature. In order to avoid pressure imbalance, the temperature is too low or too high, resulting in leakage. Regularly clean and replace the filter element to determine the composition of debris and hydraulic oil pollution.

Confirm the degree of wear and wear of the hydraulic system, and sample and test the hydraulic oil of the extruder every three months.  Check hydraulic oil viscosity, acid value, moisture, particles and other items so that reasonable measures can be taken to solve them.

三. Conclusion

Through analysis, it can be confirmed that the hydraulic system leakage of the aluminum extrusion press is mainly caused by the lack of stability of the hydraulic system. So we have to take corresponding measures.

However, solutions are always attributable to remedial measures, and cannot have a preventive effect. 

Therefore, it is of great significance to take necessary hydraulic system maintenance and management in daily work.

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What is the Application of Hydraulic Rotary point

hydraulic check damping valve manufaccturer in China

What is the Application of Hydraulic Rotary point

Hydraulic power system is widely used in the industrial field by virtue of its many advantages. When the rotating equipment needs to use hydraulic medium as the transmission power, there are strict requirements on the pressure and control accuracy of the hydraulic medium, usually a pressure above 30MP, and reliable operation.

For the development and application of rotary points, it is necessary to simplify the structure of the equipment while achieving a better conversion function. The most extensive and typical application of hydraulic rotary points is in the hot-rolled wide strip steel coilers of steel rolling equipment. And on the expansion and contraction cylinders of uncoilers, coilers and other equipment on the cold-rolled strip production line.

1. Structural principle analysis of hydraulic rotary point

1.1 Structure and Principle

The hydraulic rotary point has two control oil ports and a drain port, which are respectively connected to the fixed pipelines of the hydraulic system. Each external pipeline is statically connected to the shell of the rotary point.

The shell of the hydraulic rotary point is fixed on the shell of the matching main equipment, and keeps relatively static with the main equipment base, connected with the main equipment through the mandrel. The clearance between the outer diameter of the mandrel and the inner diameter of the hydraulic rotary joint. The gap between the cylinder barrel and the piston is required to be the same as that of the hydraulic cylinder, generally 0.04mm~0.07mm. When conditions permit, lower the limit as much as possible. Each time the hydraulic system is started, a static pressure oil film will be formed in the matching gap, which protects the mandrel and the hydraulic rotary joint from wear and tear, and plays a role of sealing.

The rotating seal is installed on the mandrel of the equipment, and its main function is to isolate the oil inlet cavity and the oil return cavity to form two independent sealed spaces. Most of the materials are wear-resistant composite materials or metal materials. Rotary seals need to withstand high pressures above 30MP, and are required to be resistant to high pressure shocks, not easy to deform, and have small leakage. The rotary seal and the inner wall of the rotary joint are not in contact, and there is fluid friction between the two.

The vibration and impact generated by the high-speed operation of the main equipment are transmitted to the hydraulic rotary joint through the mandrel, resulting in a certain swing of the rotary joint. Two bearings are used to support the axial force and radial force generated by the swing of the rotary joint housing, and to realize the precise positioning of the equipment core shaft and the rotary joint.

The end face seal adopts a skeleton lip seal, which is used to seal the leaking oil from the rotating seal. The leaking oil pressure generally does not exceed 0.3MP. Once the leakage increases, it is easy to damage the end seal and cause the hydraulic oil to leak outside. The oil port of the rotary joint shell is butted with the oil port on the mandrel of the equipment.

1.2 Analysis of internal sealing structure

There are two main types of rotary seals for rotary points, composite seals and mechanical seals. The sealing performance of the composite material seal is relatively better, and it is used where the hydraulic cylinder has an intermediate positioning. The rotary point sealed with composite materials can make the rotary point more compact and exquisite due to the small size of the seal itself. The cost of the composite seal itself is much cheaper than that of the mechanical seal.

The composite rotary seal is composed of two parts, a combination of an outer ring made of PTFE and an O-ring made of NBR. The O-ring plays the role of supporting the outer ring, making the entire rotary seal easier to install, sliding between the outer ring and the housing of the rotary joint. The manufacture of mechanical seals is more complicated, the precision requirements are also relatively high, and the relative price is relatively high.

2. Installation and maintenance of hydraulic rotary points

When installing the hydraulic rotary point on the mandrel of the main equipment, ensure that the cavity of the rotary joint and the mandrel of the main equipment have good coaxiality. It is generally required that the coaxiality between the axis of the rotary joint and the axis of the equipment should be controlled within ±1mm/m. Out-of-concentricity will cause the hydraulic rotary point to produce relatively large radial swings during high-speed rotation. The radial force causes the rotary joint and the mandrel to slide periodically in the axial direction. Not only the dynamic oil film is destroyed and the wear of the mating surface is increased, but also the end face of the seal is worn. At the same time, the bearing can withstand greater external impact. Therefore, poor coaxiality will cause great damage to the internal rotating seal and bearings, and affect the service life.

The housing of the rotary joint is fixed to prevent it from rotating synchronously with the spindle, so as long as it can be prevented from rotating in a circle.

Do not use more constraints. Radial or axial force acting on the shell will be transmitted to the bearing of the hydraulic rotary joint and the internal rotating seal through the shell, forcing the bearing or seal to wear or damage.

When connecting external oil pipes, strictly abide by the hydraulic equipment installation specifications. In particular, it is necessary to strictly check the cleanliness of each oil port to prevent external contaminants and machined burrs from being brought into the rotary joint. Due to the complex internal structure of the hydraulic rotary joint and the small matching clearance, once external contaminants enter the hydraulic rotary joint, it is easy to cause damage to the oil film, mechanical seals and bearing jams, and serious leakage.

The skeleton oil seal of the rotary joint is used to seal the rotating mandrel, so that the leaking oil of the rotary seal is drained from the leaking oil pipe to the oil tank. The pressure resistance of the oil seal is usually no more than 3bar, so the leaking oil pipe must be returned to the oil smoothly.

During installation, the leaking oil port of the rotary joint must not be blocked. If there is a valve on the leaking oil pipe, it must be opened before the medium is introduced, otherwise the oil seal will inevitably be squeezed out. It is also not possible to incorporate the leaking oil pipe into the oil return pipe, because the pressure of the oil return pipe usually exceeds 3 bar.  Do not install a filter on the leaking oil pipe. Rotary joints usually have leakage, so they can’t be used in occasions where pressure is required. The leakage of mechanical seals is greater.

Servo control can be considered when it is required to control the stroke of the hydraulic cylinder to compensate for the leakage. When the hydraulic cylinder is not positioned in the middle, the problem will be simpler, as long as the hydraulic cylinder continues to supply the medium after the hydraulic cylinder moves to the limit position.

Rotary joints are generally lubricated and cooled by medium, so it is not possible to test or drive without passing the medium. Make sure to open the leaking oil pipe after overhauling the rotary joint or related equipment. The wear or damage of hydraulic rotary joints can be estimated by measuring the leakage. The leakage of rotary joints should be monitored and tracked regularly to monitor the operating conditions of rotary joints.

3. Common faults of hydraulic rotary joints

In actual use, hydraulic rotary joints mainly have two types of faults. One fault is manifested as the internal bearing damage of the rotary joint, and the other is the external leakage of the rotary joint.

Analyze the causes of internal bearing damage, there are three main points:

1) The hydraulic oil has poor cleanliness and granularity during installation or during use, resulting in serious wear and failure of the rolling elements of the bearing;

2) When the rotary joint is installed, the installation accuracy requirements are not met, resulting in uneven force under the static load state of the bearing and excessive vibration value under the dynamic load state, causing damage to the bearing;

3) The selected hydraulic rotary joint design and manufacturing quality do not meet the requirements of the working conditions of the equipment. The reasons for leakage outside the rotary joint are:

The machining accuracy of the mating surface of the installation seal is low, which cannot meet the accuracy requirements of the seal;

The selection and installation of the seal are not suitable for the requirements of the working conditions;

The installation accuracy of the rotary joint is poor, causing excessive vibration and damage to the seal.

4. Conclusion

In practical applications, due to the complex working conditions of the main equipment and the changeable environment. When selecting a specific application, a rotary joint suitable for a wide range of loads should be selected according to the specific working conditions. In order to meet the requirements of the main equipment from low pressure and low speed to high pressure and high speed in a wide range of working conditions. The high-precision mechanical seal hydraulic rotary joint can better realize the purpose of small leakage, reliable and durable operation.

By improving the processing accuracy and technical requirements of the parts, and improving the installation accuracy, the ability of the rotary joint to adapt to high speed and high pressure can be greatly improved, and the service life can be prolonged.

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How to Correctly use hydraulic self-sealing connectors and troubleshoot?

Hydraulic Pressure Gauge Connector with 90° Elbow manufacturer in China

How to Correctly use hydraulic self-sealing connectors and troubleshoot?

With the development of construction machinery, there are more and more types of hydraulic machinery, so it is inevitable that many mechanical failures will be encountered.

Because of the different positions, the required accessories are also different, including hydraulic self-sealing joints.

In the process of using hydraulic self-sealing joints, failures will inevitably occur.

1. Common troubleshooting

(1) One side is conducting and the other side is cut off during operation,The reason is mostly caused by the difference in spring force of the two ball valve springs.

When the oil circuit is connected, the steel ball on the side with the smaller elasticity returns a long distance. The steel ball on the side with greater elasticity is not returned, and the ball valve on this side is still closed.

In addition, this failure can also occur when a side of the steel ball is stuck by debris.

The elimination method is to remove the self-sealing connector. Twist the adjusting bolts to make the springs on both sides consistent;When the steel ball is stuck by sundries, the ball valve should be disassembled to remove sundries, and then reinstalled after washing.

hydraulic fittings of shuttle valve manufaccturer in China

(2) All pipelines on both sides are cut off during operation. The reason is that the elastic force of the springs on both sides is too weak, which makes the steel ball automatically cut off under the action of hydraulic force. If the oil flow is blocked, or the internal wear of the self-sealing joint is worn, the two steel balls cannot push each other apart during normal installation.

The troubleshooting method is to turn the adjusting screw to increase the spring pre-tightening force or replace the spring; When installing the self-sealing joint, add a gasket between the two steel balls to push the two steel balls apart.

2. use correctly

(1) The gasket between the self-sealing joint and the hydraulic oil pipe joint should be kept intact. If the gasket is lost, reinstall it in time. To prevent oil leakage and air intake.

(2) When connecting the pipeline, firstly wipe the butt end of the joint body assembly and the joint sleeve assembly clean.

Then push the connecting sleeve inward. Then insert the joint body assembly into the joint sleeve assembly, and finally loosen the coupling sleeve.

The locking steel ball is dropped into the groove of the joint body and locked to ensure that the two ball valves compress the spring at the same time and push each other open to connect the oil circuit.(Note: The sealing ring between the joint body and the joint sleeve should be kept intact.)

(3) When disassembling the pipeline, push the connecting sleeve inward.

Push inward from the joint sleeve and pull out the joint body assembly from the joint sleeve assembly.

The two ball valves simultaneously quickly close the leakage of the joint sleeve assembly and the mixing of air under the action of the spring.

(4) When the self-sealing joint is disconnected, it is strictly forbidden to load the pipeline through the control handle to prevent damage to the joint or bursting of the oil pipe.

(5) In order to prevent the self-sealing joint from being contaminated by dust and muddy water, it is best to wrap the joint with a plastic bag;  When the connector is disconnected, cover the connector body and connector tightly with a cloth or plastic bag.


When the hydraulic self-sealing joint fails, do not blindly repair it.

Using it in the correct way can greatly reduce the cost of machinery and reduce unnecessary troubles.

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Why hydraulic connection adapters have oil leakage?

Hydraulic Hose Assembly and Fittings manufacturer in China

Why hydraulic connection adapters have oil leakage?

During the actual operation of the hydraulic system, hydraulic fittings oil leakage problem has always been one of the major issues affecting its normal operation.

To reduce the frequency of hydraulic equipment repairs, scientific and reasonable methods and means must be actively adopted to deal with and deal with, and comprehensively improve its overall application effect.

I. Analysis of oil leakage

Oil leakage is a common fault problem in hydraulic connection adaptors. It requires careful analysis and research to clarify the specific part of the fault, so that a good way can be found to solve it.

The main parts of hydraulic connection adaptors that have oil leakage failure include two aspects:

First, the connection between the joint body and the hydraulic parts.

Most of the oil leakage faults in this part are the use of ordinary fine thread. For the joint body and the port of the machine, sufficient sealing work needs to be done. A combination of sealing gaskets or O-rings can achieve good results.

Second, the connection part between the joint body and the steel wire braided hose joint.

Among them, the connection link mainly uses the conical surface sealing or the end surface sealing, and the O-ring can also play an effective sealing role.

It should be noted that no matter what kind of sealing method is used, oil leakage problems may occur. 90% is due to failure of the pipe joint seal, and 10% is due to vibration or unqualified tightening torque.

II.Treatment strategy of hydraulic pipe joint oil leakage fault

Facing the common oil leakage of hydraulic connection adaptors, it is necessary to actively adopt scientific and effective methods to control and deal with them, to promote its maintenance of good operating conditions and support the stable operation of hydraulic connection adaptors.

1. Choose a reasonable way considering O-ring failure

O-rings play an important role in the sealing of hydraulic connection adaptors. When some failures occur, some oil leakage problems will be caused.We need to start from the actual failure performance of the O-ring seal, combined with the possible causes of the failure, and make targeted solutions to achieve good results.

First, the small leakage phenomenon. The main reason for this problem is that the installation process has been damaged; the compression is not enough; the friction surface is relatively rough; the groove size is not suitable enough; there is a side unloading situation, and so on.

To effectively improve these problems, reasonable measures need to be adopted, such as: (1) The installation process must be carried out in strict accordance with the established specifications and hydraulic pipe joint standards to ensure that the installation effect reaches the established goals;(2) Choose a suitable sealing method and appropriately increase a certain amount of compression;(3) Carry out a comprehensive and detailed inspection of the groove surface, focusing on observing the width and depth of the groove to see if it meets the corresponding standards, and also observe whether the groove surface and the joint are matched;(4) Check with side unloading and eccentricity.

Second, the big leak. This is mainly because the actual use effect of O-rings is not good enough, There are some quality problems, including use failure, serious scratches, deterioration, uneven expansion, scrap O-rings, etc.In order to effectively improve this problem, it is necessary to replace the new sealing ring in time to ensure the sealing effect.

Third, there is too much friction. The main problem of hydraulic connection adaptors causing oil leakage is excessive friction.The main reason is that the seal compression and swelling are too large, and there is contact between metal and metal.

Effectively find a good response strategy, effectively select the seal to achieve a good fit effect, ensure that there is good compatibility between the materials, observe whether the corresponding retaining ring is required during the operation of the sealing ring, and observe whether there is no problem of excessive uneven expansion.

Fourth,  leakage at low temperatures. The amount of compression is insufficient or the material of the O-ring is not suitable enough.In view of this situation, it is necessary to select a suitable sealing ring in time, appropriately increase the amount of compression, and promote it to provide a certain guarantee for thermodynamic contraction.

Fifth, early failure. When the O-ring is actually used,If the assembly process is damaged, there is a large amount of compression,  the selected O-ring size is not correct enough, or the design groove effect is not good, then it will cause abnormal operation of the O-ring and premature failure. As a result, it will not be able to exert its proper sealing function, leading to some oil leakage failures.In response to this situation, it is necessary to actively adopt scientific and reasonable methods to deal with .

For example, the installation process is implemented in accordance with the regulations, and the specific compression amount is controlled to ensure that it has a high degree of rationality.At the same time, appropriately increase the cross-section of the O-ring and check whether the O-ring is overused.

2. Correctly select and install the O-ring

O-ring occupies an important position in the sealing work of hydraulic connection adaptors,In order to effectively improve the sealing effect of hydraulic equipment and reduce the problem of oil leakage,It is necessary to effectively use a good O-ring, choose the right and appropriate method, and install it in strict accordance with the regulations.

First, it is necessary to effectively use a good O-ring, choose the right and appropriate method, and install it in strict accordance with the regulations.

On the one hand, the groove can be stretched to a certain extent after the O-ring is installed, the joint should be well contracted after being assembled.It can be seen from previous installation experience that the cross-sectional diameter of the O-ring needs to be 0.6 to 0.9 times the width of the sealing groove.

Secondly, scientifically and standardly implement installation operations.

The actual installation effect of the O-ring will have an important impact on its service life and the actual operating effect of the hydraulic connection adapters.Therefore, it is necessary to control the actual installation operation, and reasonably control the operation of the seal ring and the seal, so that it can achieve a good match in the groove.

In most cases, installation in the manner of rectangular grooves can achieve good results. At the same time, it should be noted that the actual processing, assembly and acceptance of the sealing groove are in progress.The fillet radius of the groove edge needs to be controlled above 0.2 mm, and appropriate assembly tools should be selected to reduce the occurrence of poor connection effects of the firmware.Ensure that the sealing ring is installed in place to meet the established sealing compression requirements.

三. Conclusion

Hydraulic connection adaptors are important in the actual operation of hydraulic equipment. They are also the main parts that are prone to some oil leakage failures. They will affect the operation of the entire equipment and need to be controlled in a reasonable way.

In hydraulic connection adaptors, O-ring is one of the key parts. It is necessary to choose a reasonable method based on its failure performance, and correctly select and install the O-ring.

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What is the base work of preventive maintenance in hydraulic system?

hydraulic tubular check valve manufaccturer in China

What is the base work of preventive maintenance in hydraulic system?

The hydraulic system is widely used in processing equipment due to its unique advantages. A large number of hydraulic control components and hydraulic actuators are distributed in the processing and rolling equipment, and they play a vital role in the precision control and transmission control of the equipment.

However, the stability of the hydraulic system also directly affects the stability of the overall equipment, production efficiency, product quality and maintenance costs.To further regulate the hydraulic system maintenance and management should be based on scientific, standardized, data and information to perform routine maintenance and management of the hydraulic system.

Following is the basic work of preventive maintenance of hydraulic system.

(一) Hydraulic system point inspection

All hydraulic systems should be included in the daily point inspection management of the equipment. The hydraulic system point inspection items should cover the following 4 elements: “liquid level, pressure, temperature, vibration”.

From power components, control components, executive components to auxiliary components, all should be included in the inspection scope.The frequency of specific inspections can be determined according to the working conditions and strictly included in the maintenance procedures of each machine train.

The point inspection data is uniformly recorded in the informationized equipment management system, which is convenient for closed-loop management and control of abnormal problems and subsequent data query and analysis.

1. Inspection of liquid level points

All hydraulic system oil tanks shall have level control standards. The minimum liquid level of the hydraulic system oil tank shall not be lower than 50% of the actual height of the oil tank, and the maximum liquid level shall not be higher than 80% of the actual height of the oil tank.

In addition to checking the liquid level, record the relevant data and deal with the liquid level fluctuations compared to the previous time and within 24 hours.

2. Inspection of pressure points

Machine train equipment should be based on the hydraulic control schematic diagram, establish a hydraulic system “pressure list” and incorporate it into periodic control.

The “list of pressure values” shall cover the rated pressure of the hydraulic system, working pressure, working pressure of each control point, and pressure values of relevant relief valves.

And according to the equipment working conditions, the above-mentioned “pressure point inspection” work is reasonably divided to different positions of personnel who perform the inspection work.

3. Inspection of temperature points

The hydraulic system of the machine train equipment should establish a “temperature list” and include it in the daily inspection and control. The “temperature list” should cover key hydraulic components and parts.

According to the working conditions of the equipment, each machine train classifies the work of “temperature point inspection”, divides the frequency, and reasonably divides the work to the personnel of different positions who perform the inspection work.

4. Vibration point inspection

Vibration of the hydraulic system pipeline should be paid attention to during the point inspection. When the hydraulic system is running, except for the vibration of the hose, all hard pipes should not have visible vibration.

5. Dynamic monitoring system

For key parts, an equipment dynamic monitoring system with intelligent monitoring and analysis can be introduced, such as real-time monitoring of the temperature and vibration of the pump body.

(二)Preventive maintenance

In the work machine equipment maintenance procedures, a special “hydraulic system preventive maintenance list” should be formulated, which covers the performance inspection and maintenance of the main components of the hydraulic system, the maintenance of the cleaning filter system, the check of the pressure value of the pump and valve, the maintenance of the seal and the leakage Troubleshoot and check tightness of pipe clamps and pipe joints.

The preventive maintenance methods for the four major components of the hydraulic system are as follows:

1. Power components

As the power component of the hydraulic system, the hydraulic pump should be tested and maintained regularly.

2. Control components

Hydraulic system control components mainly perform preventive maintenance for pressure valves and flow valves. Regular pressure reducing valves, relief valves, and throttle valves should be tested once per year for the pressure regulation and throttling performance of the valves. The above-mentioned valve parts in key parts should be tested every six months.

3. operating units

The preventive maintenance of hydraulic cylinders and hydraulic motor actuators is mainly for the inspection of piston rod wear and deformation, and regular inspection or replacement of seals.In principle, the seals of hydraulic cylinders should be disassembled and inspected every 5 years, and replaced or continued to be used according to the inspection conditions.

4. Auxiliary components
(1) Fuel tank

All oil tanks of high-pressure servo hydraulic system should be cleaned at least once a year, and all oil tanks of low-pressure auxiliary hydraulic system should be cleaned once every two years.The inside of all hydraulic system oil tanks should be separated from the oil suction side and the oil return side according to the design standards, and the height of the pump suction port from the bottom of the oil tank should not be less than twice the diameter of the suction port pipe.

(2) Filter

All hydraulic systems should use filters with differential pressure indicators, and perform filter replacement and maintenance work based on the alarm conditions of the differential pressure indicators. The differential pressure indicators should be checked every six months.

The filtration accuracy of the filter element at the outlet of the pump should not be less than 7μm, and the filtration accuracy of the circulating filter system of the pump station should not be less than 5μm.

(3) Plate cooler

The heat exchange effect of the plate cooler should be checked once a month, and the execution records and data comparison of the temperature of the cooling water in and out, and the temperature of the in and out oil should be integrated. According to the data chain comparison and the cooling effect in the same season of the previous year, the plate cooler shall be disassembled and maintained.

In principle, the plate cooler should be disassembled and maintained at least once every three years.Periodic inspection and cleaning of Y-type filters of all plate cooler inlet pipes should be finished per quarter.

(4) Pipeline

The pipeline maintenance work of the hydraulic system is mainly carried out for pipe joint inspection, pipe clamp tightening inspection, hose inspection and so on.

All pipe joints and pipe clamps shall be classified and regularly tightened inspection according to the distribution of valve stations and equipment working conditions. The longest period of tightening inspection shall not exceed 1 time/quarter.The fastening of pipe joints and pipe clamps should be based on the “131” principle, that is, focus on the control of a line above the strip, within 3 meters of the execution end, and a power source output end.

The visual inspection of the hose should be carried out once per month, which can be carried out in conjunction with the periodic short-term regular inspection of the equipment.

5. Accumulator

All accumulators shall perform periodic inspection of airbag pressure, and the inspection cycle is once per quarter. The air bag inflation pressure is 70% to 75% of the working pressure of the control oil circuit of the accumulator.

(三)Leakage control of hydraulic system

  1. The machine train equipment should establish a standardized leakage control ledger, and the ledger information should cover the specific leakage location, leakage degree, approximate leakage volume, leakage point seal parameters and other information.

2. The machine train equipment should establish a list of common and key control leak points, and form a leak detection operation guide to guide the operators and electric clamp maintenance personnel to perform the hydraulic system leak detection work.

3. The electric fitters who    perform the leakage treatment of the hydraulic system shall be trained to perform the norms.

 4. For the preventive maintenance of leaks, a dedicated person should be designated to be responsible for the closed-loop management and control of standardized operations and problems.

5. For the 5S management of hydraulic system leakage, a division of responsibility system can be adopted, such as the system of appointing people and points.

 6. If the hydraulic system leakage management and control of the current month fails to achieve the control target, a relevant leakage analysis meeting should be organized and the meeting minutes should be formed; the person in charge and the completion time of the problem improvement item should be clarified, and closed-loop control and follow-up assessment should be implemented.

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What is the Reliability of conventional hydraulic systems?

TP Direct Pressure Gauge Connector for Hydraulic manufaccturer in China

What is the Reliability of conventional hydraulic systems?

Hydraulic system has the advantages of high power, small size, light weight, fast response, high precision and high rigidity against load. Therefore, it has been widely used in many important fields such as metallurgical industry, construction machinery, aerospace, shipbuilding and so on. Hydraulic systems are often at the core of control and power transmission in various equipment and systems.Therefore, it is necessary to study the reliability of the hydraulic system.

The conventional reliability research of hydraulic system is as follows:

1. Reliability design

The reliability design of the hydraulic system is the most important part of the hydraulic reliability engineering. The concept of “reliability is by design” has been recognized by people.The main reliability design methods of hydraulic systems include redundant design, energy-saving design, environment-resistant design and simplified design.

(1) Redundant design

Redundant design uses multiple systems, and when one of them has a problem, it will be removed or isolated through fault monitoring.

Redundant design can significantly improve the reliability of the system, so that it can continue to work in the event of a failure.It is generally used in places that require the system to be “absolutely” reliable, such as aerospace, nuclear power plants, large ground power stations, etc., to ensure the mission reliability of the system.

The disadvantage is that the implementation cost is high, the control model of the system is complicated, and there is a certain limit to the improvement of system reliability.The introduction of redundant units will inevitably cause additional costs. Besides it will increase manufacturing costs, use and maintenance costs.

(2) Energy-saving design

The use of new components and new technologies to realize the energy saving of the hydraulic system can reduce the installed power and failure rate.

If a new type of energy conversion element-hydraulic transformer is used, the hydraulic transformer can adjust the flow and pressure according to the load without loss. The application of hydraulic transformer to the hydraulic system not only brings about a significant reduction in the installed power of the system, but also opens up a new way for reducing system energy consumption and simplifying the structure of the hydraulic system.

(3) Environmentally resistant design

The hydraulic system that works in special environments such as the seabed, underwater, pollution, etc., must be designed for environmental resistance.

For example, conduct theoretical and practical research on the electro-hydraulic servo platform of the underwater oil storage and supply system, design a platform-type electro-hydraulic servo system that can adaptively adjust the hull posture. And do pioneering research work of anti-corrosion and seal the hydraulic components and systems in the marine environment.

(4) Simplified Design

The simplified design can improve the basic reliability of the product. The hydraulic system should use the integrated design of pumps, valves, and tanks as much as possible to reduce pipeline connections. Use unitized and modular design as much as possible to reduce the number of product components and their mutual connections.

As far as possible to achieve the standardization, serialization and generalization of parts and components, and strive to achieve multiple functions with fewer parts and components.

2. eliability prediction

Predicting the reliability of a system is an important parameter to measure the pros and cons of a system and whether it meets the task requirements, and it is also an important means of mutual evaluation between systems.

The reliability prediction of the hydraulic system can generally be predicted by the mathematical model method plus the correction coefficient.

3. Reliability analysis

(1) Fault tree analysis

Fault tree analysis technology is widely used, especially in the fields of nuclear industry, aerospace, machinery and electronics, weapons, ships, chemical industry, etc. It plays an important role in improving the safety and reliability of products.

Fault tree analysis is gradually applied and researched in the reliability, safety, and fault analysis and diagnosis of hydraulic systems. For example, the research on the hydraulic system of crane travel is proposed, and a method of qualitative analysis of the fault tree using the minimum cut-set matrix and the calculation of structural importance is proposed. The fault tree analysis of the hydraulic system of the main cylinder of the hydraulic press is carried out, and the improvement measures of the hydraulic system are proposed based on the analysis results.

(2) GO method

GO method is a success-oriented reliability analysis method. The GO method uses the GO graph to simulate the system, and the GO graph can directly calculate the system’s success probability. For systems with multiple states and timing, it can solve the reliability problems of complex systems that are incapable of fault tree methods. For example, the GO method is used to carry out qualitative analysis and quantitative calculation of the reliability of the hydraulic system of the loader, and the reliability of the hydraulic system is quantitatively evaluated.

4. summary

With the development of hydraulic systems in the direction of rapid, high-power, and high-precision, hydraulic systems and equipment have more and more functions, structures and information are becoming more and more complex, performance indicators are getting higher and higher, and the work intensity is getting heavier and heavier. The relationship is getting closer.

This situation has brought about two results. On the one hand, productivity and product quality have been improved; on the other hand, the probability of failure has also increased.

 Once the hydraulic system fails, it will cause heavy losses. Therefore, it is of great significance to study the reliability of the hydraulic system.

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How to eliminate mechanical vibration generated in hydraulic system?

hydraulic fittings of shuttle valve manufaccturer in China

How to eliminate mechanical vibration generated in hydraulic system?

Vibration is a phenomenon that often appear in the hydraulic system, which is mainly from two aspects: the mechanical vibration generated by the motion of the system, and the working fluid generated in the process.

Most hydraulic vibration systems are very harmful, of course, except for the use of hydraulic devices operating on the principle of vibration. The vibration adirectly affect the working performance of the hydraulic system, causing damage to the hydraulic components, and accessories line, thereby shortening the system service life.

一. Reasons for vibration of mechanical system

1. Unbalanced rotors

When the prime mover, hydraulic pump, hydraulic motor and so on rotate at high speed, if the shaft imbalance, it will have periodic unbalanced force. Thereby this mechanical vibration  will also cause a series of vibrations to integrated block or other pipelines when mounting base line.

2. Two-axis connection is not concentric

When the prime mover is connected to the hydraulic pump and the hydraulic motor to the load through the coupling, if the coupling is deviated or the rotating shaft is not strong due to the different axis of the connected part, vibration will occur.

3. Improper bearing clearance

During the installation process, if the bearing is selected improperly or the bearing clearance is adjusted improperly, it will cause mechanical vibration. At the same time, when the prime mover, hydraulic pump, and hydraulic motor are in operation, the increase in bearing clearance due to wear and the loosening of fasteners will also cause mechanical vibration.

二. Measures to eliminate mechanical vibration

  1. For the vibration caused by the unbalance of the rotating body, the prime mover, hydraulic pump and hydraulic motor can be selected as far as possible under the premise of meeting the requirements of use.
  1. For the vibration caused by the non-concentricity of the rotating shaft after installation, in addition to the reasonable design of the space installation structure of the connected parts and ensuring the quality of the parts, it is best to design a connected parts as a structure that can be adjusted in the spatial position of the rotating shaft. It will be convenient to adjust when facilitate installation, to ensure good concentricity.
  1. For the vibration caused by the improper bearing clearance, in addition to the selection of the bearing (high-precision bearings have high rotation accuracy, stable operation, and small vibration after equipment installation, but this will increase the manufacturing cost of the equipment, which needs to be considered). When designing the bearing support structure, choose a structure with a gap that is easy to adjust as much as possible.


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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How to Inspect and maintain Hydraulic System?

hydraulic hose damping valve manufaccturer in China

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?

TB Hydraulic Test Coupling with Tube manufaccturer in China

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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