Leakage Reasons and Exclusion of Hydraulic System
2023-03-10 13:09:38
First, the elimination of hydraulic leakage fault
Hydraulic oil leakage will cause the hydraulic pressure to decrease and the normal oil pressure cannot be established, resulting in the system not working properly. There are two kinds of leaks in the hydraulic system: leakage and internal leakage. This article describes how to eliminate internal leakage faults in the hydraulic system.
Hydraulic oil leakage will cause hydraulic pressure to decrease and normal oil pressure cannot be established, resulting in the system not working properly.
There are two kinds of leaks in the hydraulic system: leakage and internal leakage. Leakage is mainly caused by broken tubing, loose joints, tight fastening, etc.; internal leakage is mainly caused by leakage of oil pumps, oil cylinders, distributors, etc. inside the hydraulic system. Internal leakage faults are not easily found, and sometimes Need to use the instrument to detect and adjust before it can be eliminated.
1. The relevant parts of the gear pump are seriously worn or assembled. (1) The clearance between the pump gear and the pump housing exceeds the specified limit. The treatment method is: replace the pump casing or repair with the inserting method to ensure that the clearance between the gear pump top and the housing is within the specified range.
(2) Excessive wear of the gear shaft sleeve and the gear end face causes the pre-compression amount of the pressure relief seal ring to lose its sealing effect, resulting in the collusion of the high-pressure oil chamber of the oil pump and the low-pressure oil chamber, resulting in serious internal leakage. The processing method is: add compensating gasket under the rear axle sleeve (the thickness of the compensating gasket should not exceed 2mm generally), and guarantee the compression amount of the sealing ring.
(3) When disassembling the oil pump, install the guide wire in the wrong direction at the joint surface of the 2 bushings (sleeve of spiral oil groove). The treatment method is to ensure that the guide wire can simultaneously deflect two bushings at an angle in the direction of rotation of the driven gear, so that the two bushings are closely attached.
(4) When disassembling the oil pump, the pressure-isolating seal ring is aged and damaged, and the relieving plate seal apron is installed incorrectly. The treatment method is as follows: If the pressure-insulated sealing ring is aged, replace it with a new one: The pressure-relief-plate sealing apron should be installed on the suction chamber (mouth) side (low-pressure chamber) and ensure that there is a certain preload pressure. If installed on the pressure chamber side, the seal apron will be damaged quickly, causing the high-pressure chamber to communicate with the low-pressure chamber, making the oil pump inoperative.
2. Aging and damage of the cylinder seal ring Looseness of the piston rod lock nut (1) The seal ring on the piston of the cylinder, the seal ring of the piston rod and the piston joint, and the positioning valve seal ring are damaged. The treatment method is: replace the seal ring and seal ring. However, it should be noted that the surface of the selected seal ring should be smooth; no wrinkles, no cracks, no air holes, no scratches, etc.
(2) The piston rod lock nut is loose. The treatment is: Tighten the piston rod lock nut.
(3) If cylinder misalignment is serious, the hydraulic fluid in the upper and lower chambers of the cylinder may be connected. Treatment method: If the loss of circle is not serious, you can replace it by increasing the piston seal to restore its tightness; if the roundness, cylindricity error exceeds 0.05mm, the cylinder should be honed, replace the piston to increase , to restore normal fit clearance.
3. The safety valve and return valve on the distributor do not close tightly (1) The safety valve is worn or the hydraulic oil is dirty; the ball valve is rusted and the spring force is insufficient or broken; the hydraulic oil is out of specification; the hydraulic oil is too thin or the oil temperature is too high. High (the normal temperature of the hydraulic oil should be 30 °C ~ 60 °C) will make the safety valve close. The treatment method is: replace the clean hydraulic oil that meets the standard; replace the spring with the specified length and elasticity; replace the ball in the ball valve, insert it into the valve seat, knock it, make it fit with the valve seat, and perform grinding.
(2) The return valve has worn out or the return valve is closed due to dirty hydraulic oil. The processing method is: grinding cone surface and mutual grinding valve seat. If the cylindrical surface is seriously worn, it can be repaired by chrome plating. If the small cylinder surface and the pipe are worn, the internal clearance is too large. The copper sleeve can be inserted into the pipe and the clearance can be restored. Clean the cylinder and replace the clean hydraulic oil.
The slide valve and the slide valve hole wear, so that the gap increases, the oil in the oil cylinder under the action of the piston from the wear gap leakage, flow back to the tank. The processing method is: After the chrome plating grinding repair, matching with the slide valve hole.
Second, the main parts and causes of leakage outside the hydraulic system can be summarized as follows:
1) Pipe joints and oil plugs are used more often in hydraulic systems, and they also account for a high proportion of oil spill accidents, up to 30% to 40%. Most of the oil leakage from the fittings occurs at the joints with other parts, such as manifolds, valve bottom plates, tubular elements, etc., and the fitting joints. When the pipe fittings are connected with metric thread, the centerline of the screw hole is not perpendicular to the sealing plane, ie When the screw hole geometry accuracy and machining size accuracy do not meet the requirements, it will cause the combination gasket to leak tightly. When the pipe joints are connected by the taper pipe thread, the taper between the taper pipe thread and the screw plug cannot be completely sealed. If the thread hole processing size and processing accuracy are poor, oil leakage can easily occur. If the above two conditions are difficult to cure, they can only be filled and sealed with liquid sealant or Teflon tape. The oil leakage at the nut of the coupling is generally related to the quality of the processing. For example, if the sealing groove is out of tolerance, the processing accuracy is not enough. The bumps and scratches on the sealing part can cause leakage. Must be carefully dealt with to eliminate the existing problems in order to achieve the sealing effect.
2) Leakage of joints, such as components, is also common. For example, plate valves, superimposed valves, valve covers, and method flanges are all examples of such seals. The oil leakage between the joints is mainly caused by several problems: the mounting plane in contact with the o-rings has rough processing, bumps, scratches, o-ring groove diameter, and deep depth, resulting in insufficient compression of the seal ring. The low roughness of the bottom flat surface of the groove, the inconsistent depth of the grooves on the same bottom plane, the length of the mounting screw, the insufficient strength, or the poor hole position all cause the sealing surface to be lax and lead to oil leakage. Solution: Deal with the above issues separately, supplement the o-ring groove processing, strictly control the depth dimension, improve the roughness and cleanliness of the bottom plane of the groove and the installation plane, and eliminate the lax sealing surface phenomenon.
3) Oil leakage from the axial sliding surface is difficult to solve. There are many causes of oil leaks in hydraulic cylinders, such as sticky muddy water on the surface of piston rods, salt spray, oversized sealing grooves, bumps on the surface, scratches, rough processing, low temperature hardening of seals, partial load, etc. Causes seal damage and failure to cause oil leakage. The solution can be made from several aspects of design, manufacture, and use. For example, seals with good dust resistance, wear resistance and low temperature resistance are selected, and the size and accuracy of the sealing groove are ensured. The roughness of the sliding surface is properly selected and dust is set. Retractable sleeve, try not to make the hydraulic cylinder withstand partial load, often erase the dust on the piston rod, pay attention to avoid bumps, scratches, do a good job of cleanliness management of hydraulic oil.
4) The oil leakage at the rotary shaft of the pump and motor is mainly too small with the internal diameter of the oil seal, the size of the oil seal seat is too bad, the speed is too high, the oil temperature is high, the back pressure is large, the surface roughness of the shaft is poor, and the eccentricity of the shaft is large , Poor seal compatibility with the media and unreasonable installation and other factors. The solution can be prevented from the design, manufacture, use, and control the leakage. If the appropriate internal seal interference is considered in the design, the dimensional accuracy of the oil seal seat can be guaranteed, and the seal seat can be filled with sealant during assembly. Designed according to the pump speed, oil temperature and medium, select the appropriate sealing material processing oil seal, improve the roughness of the contact surface with the oil seal and assembly quality.
5) Temperature rise and heat often cause serious leakage in the hydraulic system. It can make the viscosity of the oil drop or deteriorate, so that the internal leakage increases. As the temperature continues to increase, it will cause the sealing material to expand after being heated and increase the friction force. Faster wear causes leaks in the axial rotation or sliding parts. The o-rings in the sealing area are also thermally aged due to high temperature, increased expansion and deformation, and they cannot be restored to their original shape after cooling. As a result, the sealing ring loses its elasticity and fails due to insufficient compression, resulting in gradual leakage. Therefore, controlling the temperature rise is very important for the hydraulic system. There are many causes of temperature rise, such as temperature rise caused by mechanical friction, temperature rise caused by pressure and volume loss, and temperature rise caused by poor heat dissipation conditions. In order to reduce the leakage caused by heat rise and heat, first of all, from the perspective of optimal design of the hydraulic system, design a high-efficiency energy-saving circuit, improve the processing and assembly quality of hydraulic components, and reduce the energy loss caused by internal leakage. Use a working medium with good viscosity-temperature characteristics to reduce internal leakage. The influence of the external heat source of the compartment on the system will increase the heat dissipation area of ​​the fuel tank. If necessary, the cooler will be installed to strictly control the oil temperature of the system between 25 and 50°C.
Third, the main measures for leak prevention and leakage of hydraulic systems are as follows:
1) Minimize the number of oil line pipe joints and flanges. In the design, the superposition valve, cartridge valve, and plate valve are widely used. In the form of integrated block combination, the leakage point of the pipeline is reduced, which is one of the effective measures for preventing leakage. .
2) Install the hydraulic valve platform in the hydraulic system close to the actuator, which can greatly shorten the total length of the hydraulic pipeline, thereby reducing the number of pipe joints.
3) Hydraulic shocks and mechanical vibrations directly or indirectly affect the system, resulting in loose pipe joints and leakage. Hydraulic shocks are often caused by rapid commutation. Therefore, as long as the working conditions permit, try to extend the reversing time, that is, the valve core is provided with a buffer groove, a buffer cone structure or a control valve equipped with a valve that extends the reversing time. The hydraulic system should be kept away from external sources of vibration. Pipes should be set up with reasonable pipe clamps. Pumps can be equipped with shock absorbers, high-pressure hoses, compensation pipes or pulsating absorbers to eliminate pressure pulsations and reduce vibration.
4) Regular inspections, regular maintenance, and timely handling are the basic guarantees for preventing leakage and reducing failures.
Hydraulic oil leakage will cause the hydraulic pressure to decrease and the normal oil pressure cannot be established, resulting in the system not working properly. There are two kinds of leaks in the hydraulic system: leakage and internal leakage. This article describes how to eliminate internal leakage faults in the hydraulic system.
Hydraulic oil leakage will cause hydraulic pressure to decrease and normal oil pressure cannot be established, resulting in the system not working properly.
There are two kinds of leaks in the hydraulic system: leakage and internal leakage. Leakage is mainly caused by broken tubing, loose joints, tight fastening, etc.; internal leakage is mainly caused by leakage of oil pumps, oil cylinders, distributors, etc. inside the hydraulic system. Internal leakage faults are not easily found, and sometimes Need to use the instrument to detect and adjust before it can be eliminated.
1. The relevant parts of the gear pump are seriously worn or assembled. (1) The clearance between the pump gear and the pump housing exceeds the specified limit. The treatment method is: replace the pump casing or repair with the inserting method to ensure that the clearance between the gear pump top and the housing is within the specified range.
(2) Excessive wear of the gear shaft sleeve and the gear end face causes the pre-compression amount of the pressure relief seal ring to lose its sealing effect, resulting in the collusion of the high-pressure oil chamber of the oil pump and the low-pressure oil chamber, resulting in serious internal leakage. The processing method is: add compensating gasket under the rear axle sleeve (the thickness of the compensating gasket should not exceed 2mm generally), and guarantee the compression amount of the sealing ring.
(3) When disassembling the oil pump, install the guide wire in the wrong direction at the joint surface of the 2 bushings (sleeve of spiral oil groove). The treatment method is to ensure that the guide wire can simultaneously deflect two bushings at an angle in the direction of rotation of the driven gear, so that the two bushings are closely attached.
(4) When disassembling the oil pump, the pressure-isolating seal ring is aged and damaged, and the relieving plate seal apron is installed incorrectly. The treatment method is as follows: If the pressure-insulated sealing ring is aged, replace it with a new one: The pressure-relief-plate sealing apron should be installed on the suction chamber (mouth) side (low-pressure chamber) and ensure that there is a certain preload pressure. If installed on the pressure chamber side, the seal apron will be damaged quickly, causing the high-pressure chamber to communicate with the low-pressure chamber, making the oil pump inoperative.
2. Aging and damage of the cylinder seal ring Looseness of the piston rod lock nut (1) The seal ring on the piston of the cylinder, the seal ring of the piston rod and the piston joint, and the positioning valve seal ring are damaged. The treatment method is: replace the seal ring and seal ring. However, it should be noted that the surface of the selected seal ring should be smooth; no wrinkles, no cracks, no air holes, no scratches, etc.
(2) The piston rod lock nut is loose. The treatment is: Tighten the piston rod lock nut.
(3) If cylinder misalignment is serious, the hydraulic fluid in the upper and lower chambers of the cylinder may be connected. Treatment method: If the loss of circle is not serious, you can replace it by increasing the piston seal to restore its tightness; if the roundness, cylindricity error exceeds 0.05mm, the cylinder should be honed, replace the piston to increase , to restore normal fit clearance.
3. The safety valve and return valve on the distributor do not close tightly (1) The safety valve is worn or the hydraulic oil is dirty; the ball valve is rusted and the spring force is insufficient or broken; the hydraulic oil is out of specification; the hydraulic oil is too thin or the oil temperature is too high. High (the normal temperature of the hydraulic oil should be 30 °C ~ 60 °C) will make the safety valve close. The treatment method is: replace the clean hydraulic oil that meets the standard; replace the spring with the specified length and elasticity; replace the ball in the ball valve, insert it into the valve seat, knock it, make it fit with the valve seat, and perform grinding.
(2) The return valve has worn out or the return valve is closed due to dirty hydraulic oil. The processing method is: grinding cone surface and mutual grinding valve seat. If the cylindrical surface is seriously worn, it can be repaired by chrome plating. If the small cylinder surface and the pipe are worn, the internal clearance is too large. The copper sleeve can be inserted into the pipe and the clearance can be restored. Clean the cylinder and replace the clean hydraulic oil.
The slide valve and the slide valve hole wear, so that the gap increases, the oil in the oil cylinder under the action of the piston from the wear gap leakage, flow back to the tank. The processing method is: After the chrome plating grinding repair, matching with the slide valve hole.
Second, the main parts and causes of leakage outside the hydraulic system can be summarized as follows:
1) Pipe joints and oil plugs are used more often in hydraulic systems, and they also account for a high proportion of oil spill accidents, up to 30% to 40%. Most of the oil leakage from the fittings occurs at the joints with other parts, such as manifolds, valve bottom plates, tubular elements, etc., and the fitting joints. When the pipe fittings are connected with metric thread, the centerline of the screw hole is not perpendicular to the sealing plane, ie When the screw hole geometry accuracy and machining size accuracy do not meet the requirements, it will cause the combination gasket to leak tightly. When the pipe joints are connected by the taper pipe thread, the taper between the taper pipe thread and the screw plug cannot be completely sealed. If the thread hole processing size and processing accuracy are poor, oil leakage can easily occur. If the above two conditions are difficult to cure, they can only be filled and sealed with liquid sealant or Teflon tape. The oil leakage at the nut of the coupling is generally related to the quality of the processing. For example, if the sealing groove is out of tolerance, the processing accuracy is not enough. The bumps and scratches on the sealing part can cause leakage. Must be carefully dealt with to eliminate the existing problems in order to achieve the sealing effect.
2) Leakage of joints, such as components, is also common. For example, plate valves, superimposed valves, valve covers, and method flanges are all examples of such seals. The oil leakage between the joints is mainly caused by several problems: the mounting plane in contact with the o-rings has rough processing, bumps, scratches, o-ring groove diameter, and deep depth, resulting in insufficient compression of the seal ring. The low roughness of the bottom flat surface of the groove, the inconsistent depth of the grooves on the same bottom plane, the length of the mounting screw, the insufficient strength, or the poor hole position all cause the sealing surface to be lax and lead to oil leakage. Solution: Deal with the above issues separately, supplement the o-ring groove processing, strictly control the depth dimension, improve the roughness and cleanliness of the bottom plane of the groove and the installation plane, and eliminate the lax sealing surface phenomenon.
3) Oil leakage from the axial sliding surface is difficult to solve. There are many causes of oil leaks in hydraulic cylinders, such as sticky muddy water on the surface of piston rods, salt spray, oversized sealing grooves, bumps on the surface, scratches, rough processing, low temperature hardening of seals, partial load, etc. Causes seal damage and failure to cause oil leakage. The solution can be made from several aspects of design, manufacture, and use. For example, seals with good dust resistance, wear resistance and low temperature resistance are selected, and the size and accuracy of the sealing groove are ensured. The roughness of the sliding surface is properly selected and dust is set. Retractable sleeve, try not to make the hydraulic cylinder withstand partial load, often erase the dust on the piston rod, pay attention to avoid bumps, scratches, do a good job of cleanliness management of hydraulic oil.
4) The oil leakage at the rotary shaft of the pump and motor is mainly too small with the internal diameter of the oil seal, the size of the oil seal seat is too bad, the speed is too high, the oil temperature is high, the back pressure is large, the surface roughness of the shaft is poor, and the eccentricity of the shaft is large , Poor seal compatibility with the media and unreasonable installation and other factors. The solution can be prevented from the design, manufacture, use, and control the leakage. If the appropriate internal seal interference is considered in the design, the dimensional accuracy of the oil seal seat can be guaranteed, and the seal seat can be filled with sealant during assembly. Designed according to the pump speed, oil temperature and medium, select the appropriate sealing material processing oil seal, improve the roughness of the contact surface with the oil seal and assembly quality.
5) Temperature rise and heat often cause serious leakage in the hydraulic system. It can make the viscosity of the oil drop or deteriorate, so that the internal leakage increases. As the temperature continues to increase, it will cause the sealing material to expand after being heated and increase the friction force. Faster wear causes leaks in the axial rotation or sliding parts. The o-rings in the sealing area are also thermally aged due to high temperature, increased expansion and deformation, and they cannot be restored to their original shape after cooling. As a result, the sealing ring loses its elasticity and fails due to insufficient compression, resulting in gradual leakage. Therefore, controlling the temperature rise is very important for the hydraulic system. There are many causes of temperature rise, such as temperature rise caused by mechanical friction, temperature rise caused by pressure and volume loss, and temperature rise caused by poor heat dissipation conditions. In order to reduce the leakage caused by heat rise and heat, first of all, from the perspective of optimal design of the hydraulic system, design a high-efficiency energy-saving circuit, improve the processing and assembly quality of hydraulic components, and reduce the energy loss caused by internal leakage. Use a working medium with good viscosity-temperature characteristics to reduce internal leakage. The influence of the external heat source of the compartment on the system will increase the heat dissipation area of ​​the fuel tank. If necessary, the cooler will be installed to strictly control the oil temperature of the system between 25 and 50°C.
Third, the main measures for leak prevention and leakage of hydraulic systems are as follows:
1) Minimize the number of oil line pipe joints and flanges. In the design, the superposition valve, cartridge valve, and plate valve are widely used. In the form of integrated block combination, the leakage point of the pipeline is reduced, which is one of the effective measures for preventing leakage. .
2) Install the hydraulic valve platform in the hydraulic system close to the actuator, which can greatly shorten the total length of the hydraulic pipeline, thereby reducing the number of pipe joints.
3) Hydraulic shocks and mechanical vibrations directly or indirectly affect the system, resulting in loose pipe joints and leakage. Hydraulic shocks are often caused by rapid commutation. Therefore, as long as the working conditions permit, try to extend the reversing time, that is, the valve core is provided with a buffer groove, a buffer cone structure or a control valve equipped with a valve that extends the reversing time. The hydraulic system should be kept away from external sources of vibration. Pipes should be set up with reasonable pipe clamps. Pumps can be equipped with shock absorbers, high-pressure hoses, compensation pipes or pulsating absorbers to eliminate pressure pulsations and reduce vibration.
4) Regular inspections, regular maintenance, and timely handling are the basic guarantees for preventing leakage and reducing failures.
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