Fault Analysis and Treatment of Small Excavators
Posted: Feb 7th, '25, 01:31
1. Small excavator has no digging power
The digging power is determined by the output pressure of the main pump. Whether the engine load is light or heavy depends on the relationship between the oil pump absorption torque and the engine output torque. The oil pump absorption torque is small and the engine load is light.
(I) Digging power is weak when the engine load is very light. If the working speed of the small excavator is not obviously abnormal, the maximum output pressure of the main pump, that is, the system overflow pressure, should be checked. If the overflow pressure measurement value is lower than the specified value, it indicates that the overload overflow setting value of the hydraulic circuit of the mechanism is incorrect, resulting in premature overflow of the mechanism and no working power. The machine can be adjusted by turning the adjustment screw.
(2) Digging power is weak when the engine self-load is very heavy. When the boom or dipper is extended to the bottom, the digging power is weak, and even the engine is turned off. The absorption torque of the oil pump is greater than the engine output torque. This indicates that the engine is overloaded. This kind of fault should first check whether the engine speed sensing system is normal. After the above detailed inspection and troubleshooting, the engine speed sensing system will resume normal function and the digging power will return to normal.
2. Transmission jumps during operation
Transmission jumps during operation of small excavators refers to the automatic jump of the transmission transmission mechanism from a certain driving gear to neutral gear, which causes the machine's driving speed to lose control. Transmission jumps are very harmful and timely measures must be taken to prevent accidents.
(1) Analysis of the cause of transmission jumps. Small excavators mostly use a mechanical shifting transmission mechanism. This transmission mechanism relies on the sliding gear sleeve to move axially on the fixed gear sleeve r and mesh with the driven gears of each gear to achieve gear shifting. During frequent gear shifting, the gear end faces of the above-mentioned meshing gears are easily worn into a cone, causing their meshing performance to decrease and cause jumps. Sudden changes in external loads can cause the transmission to jump. When the road surface is uneven, the machine is driving downhill or the driving route is improper, causing a sudden change in external load, this sudden change in load will act on the gear meshing gear of the transmission through the wheels and the drive shaft, causing the gear meshing gear to generate axial thrust and disengage, causing the transmission to jump. When a small excavator is driving on a slope, improper operation may also cause the transmission to jump gears.
(2) Handling of gear jumps during the working process. When driving on a flat road, the machine can be stopped according to the normal shutdown method, and the original field can be carefully found to eliminate the fault: when driving uphill, the gear position can be set to the low speed position or the 1st gear position, and the machine can be stopped when it reaches the top of the slope to eliminate the fault; if the downshift is unsuccessful or the gear jump occurs again, the machine should be stopped according to the slope shutdown action and requirements, and then the fault should be eliminated; when driving downhill, the gear position should be set to the high speed position or the gear grabbing (emergency gear) measures should be taken according to the gear upshift action, and the machine should be stopped for inspection after it reaches the bottom of the slope to eliminate the fault; if the gear upshift is unsuccessful or the gear jump occurs once (at this time, it is the home gear), the driver can control the engine speed at medium speed (to prevent the engine from stalling), use the chopping method to slide the machine to the bottom of the slope, and then eliminate the fault. If the gear shifting or grabbing fails or the gear jump occurs again (at this time, it is neutral), and the machine is on a steep slope (at this time, the machine will dive to the bottom of the slope at a very fast speed), it should be stopped quickly according to the downhill parking instructions and requirements, and then the fault should be eliminated.
(3) Preventive measures for transmission gear jump. Strictly follow the operating procedures and driving instructions to operate, try to avoid gear knocking during gear shifting to reduce the wear of the gear pair; strictly implement the maintenance system and strengthen the maintenance of the gear shifting device. When the gear shifting device rod system is not properly connected, it should be repaired in time to ensure that the gear shifting device performs well; pay attention to the repair and maintenance of the self-locking mechanism, and repair or replace the positioning steel balls, springs and shift fork shafts that have reduced or lost their positioning efficiency in time to ensure that the self-locking performance of the self-locking mechanism is in good condition; when assembling the transmission, it should be operated strictly according to the operating procedures to ensure that the various parts of the transmission are adjusted correctly and tightened appropriately. When driving on a large downhill road, the driver should strictly follow the downhill action instructions to operate, and must not operate in violation of regulations.
Fault analysis and treatment of small excavators
3. The boom cannot be lifted with load
(1) Fault reason. The boom of a small excavator cannot be lifted with load. Generally speaking, the main reason is that the main components of its hydraulic system are seriously worn. For example, the hydraulic pump is seriously worn, and the pump leaks seriously when running at high speed; the pump pressure is slightly increased when running at high speed, but due to the wear and leakage of the pump, the volumetric efficiency is significantly reduced, and it is difficult to reach the rated pressure. The long-term operation of the hydraulic pump aggravates the wear and the oil temperature rises, which causes the wear of hydraulic components and the aging and damage of seals, loss of sealing ability, and deterioration of hydraulic oil, leading to the occurrence of faults.
(2) Fault finding and repair. The first is to check the internal leakage of the boom cylinder. The simplest way is to raise the boom to see if it has obvious free fall. If the fall is obvious, disassemble the cylinder for inspection. If the seal is worn, it should be replaced; the second is to check the control valve. First, clean the safety valve and check whether the valve core is worn. If it is worn, it should be replaced. If there is still no change after the safety valve is installed, check the wear of the control valve core. The clearance limit is generally 0.06mm. If it is seriously worn, it should be replaced. Measure the pressure of the hydraulic pump. If the pressure is low, adjust it. If the pressure cannot be adjusted, it means that the hydraulic pump is seriously worn.
4. The boom is lifted slowly and weakly
The boom of the hydraulic small excavator moves slowly, and the rest of the movements are normal. Common reasons are that the pressure of the two pumps supplying hydraulic oil to the boom is too low; the set pressure of the main control valve of the boom is too low; the boom operating valve is stuck and cannot be fully opened; the seal of the boom cylinder is damaged, and the internal or external leakage is serious.
(1) Internal leakage distribution valve leakage. The main reasons for internal leakage are: the main valve core of the total safety valve is stuck, the clearance between the valve stem and the valve body is too large, the pressure regulating spring is damaged, the seal inside the valve is damaged, or there are sand holes in the valve body, etc. Disassemble and inspect whether the cone valve of the main safety valve is stuck and clean it: Check the matching clearance between the valve stem and the valve body. The normal matching clearance should be between 0.005 and 0.012 mm. If the covering clearance exceeds the tolerance, it should be chrome-plated and ground; check the pressure spring to see if the seal inside the valve is damaged; check whether the valve body has casting defects such as sand holes.
(2) Piston seal ring damage and gear pump wear. Damage to the piston seal ring of the boom hydraulic cylinder causes internal leakage. When the boom cylinder piston is retracted to the bottom, remove the rodless cavity oil pipe and continue to fill the boom cylinder with oil. If a large amount of working oil leaks out of the rodless cavity oil port, it means that the piston seal ring is damaged and should be replaced immediately. Disassemble and inspect the gear pump end face clearance, gear meshing clearance, radial clearance between the gear and the pump body, and internal seals of the gear pump to see if they are normal. Impurities in the hydraulic oil are the main cause of the grinding of the gear pump side plate. Blockage of the oil suction line and the oil filter will also cause the system pressure to drop, causing the boom to lift slowly and weakly.
(3) Leakage of the boom hydraulic cylinder. Check whether the valve core of the operating valve moves flexibly within the stroke. If the valve core is stuck or the oil leaks here, clean the valve or replace the seal at this part. If the fault still cannot be eliminated, finally disassemble and inspect the boom hydraulic cylinder, replace the seal, solve the problem of internal or external leakage of the hydraulic cylinder, and the fault can be eliminated.
(4) Oil overflows from the gearbox breather. The oil seal of the corresponding pump should be replaced in time, and the fault should be eliminated at one time when the machine is shut down for maintenance. Otherwise, repeated maintenance will inevitably waste a lot of lubricating oil and repair time. The maintenance process of hydraulic components must be kept clean and hygienic. After the fault is eliminated, first check the gear oil and hydraulic oil levels, and add them if they are insufficient. The engine must be started after opening the hydraulic oil tank switch valve, otherwise the gearbox or main pump may be damaged or even scrapped due to lack of oil. When troubleshooting the hydraulic system, the engine should be turned off first.
Fault analysis and treatment of small excavators
5 Unable to rotate and the rotation angle is too large When the small excavator is working, other working devices operate normally, but the upper body cannot rotate. The rotation failure of the upper body of a small excavator is related to the main pump, self-pressure reducing valve, swing operating handle, swing lock switch, swing lock solenoid valve, swing motor, swing reducer, swing bearing, etc. Fault detection should be analyzed and eliminated one by one according to the principle of simple to complex.
(1) Check the swing solenoid valve control oil circuit. If only the upper body cannot rotate and other working devices operate normally, it means that the main pump and self-pressure reducing valve are not faulty. If the swing reducer or swing support fails, there will definitely be abnormal noise or vibration. If there is abnormal noise or vibration, it may be a problem with the swing reducer or swing support. Check whether the swing control pressure value is within the normal range. Then check the swing main valve core. The main valve core should move flexibly in the valve body without sticking, which means that the main oil circuit can smoothly reach the swing motor. Check the swing lock switch and measure the voltage at both ends of the switch and the resistance of the swing lock solenoid valve coil to see if the voltage or resistance is normal. If it is normal, connect a three-way joint at the outlet of the swing solenoid valve control oil circuit and connect a 4MPa pressure gauge, operate the small excavator to swing, if the pressure here is too low, it means that the oil pressure flowing to release the brake is too low, the brake cannot be removed, and the small excavator cannot swing. If there is a fault, the valve core should be removed, the components should be cleaned, and the test run after reinstallation can eliminate the fault.
(2) Brake return oil circuit inspection. When the small excavator swing operation is completed and the operating handle is in the middle position, the small excavator swings too far under the action of inertia and cannot stop at the predetermined position. This phenomenon is mostly caused by untimely swing braking or insufficient braking force. It is related to the oil pressure for releasing the brake and components such as the swing locking solenoid valve, swing brake pads and brake seals. When checking the brake oil return line, it was found that there were colloidal particles in the throttle hole of the oil return line. Although the throttle hole was not completely blocked, it caused the oil return to be too slow, which delayed the time for the brake part to take effect, so that the slippage (i.e. the rotation angle) when the upper part stopped rotating was too large. Clean all components, especially the throttle hole and small oil channel. After installing all components and testing the machine, the rotation slippage can be within the specified range, and the fault can be eliminated.
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The digging power is determined by the output pressure of the main pump. Whether the engine load is light or heavy depends on the relationship between the oil pump absorption torque and the engine output torque. The oil pump absorption torque is small and the engine load is light.
(I) Digging power is weak when the engine load is very light. If the working speed of the small excavator is not obviously abnormal, the maximum output pressure of the main pump, that is, the system overflow pressure, should be checked. If the overflow pressure measurement value is lower than the specified value, it indicates that the overload overflow setting value of the hydraulic circuit of the mechanism is incorrect, resulting in premature overflow of the mechanism and no working power. The machine can be adjusted by turning the adjustment screw.
(2) Digging power is weak when the engine self-load is very heavy. When the boom or dipper is extended to the bottom, the digging power is weak, and even the engine is turned off. The absorption torque of the oil pump is greater than the engine output torque. This indicates that the engine is overloaded. This kind of fault should first check whether the engine speed sensing system is normal. After the above detailed inspection and troubleshooting, the engine speed sensing system will resume normal function and the digging power will return to normal.
2. Transmission jumps during operation
Transmission jumps during operation of small excavators refers to the automatic jump of the transmission transmission mechanism from a certain driving gear to neutral gear, which causes the machine's driving speed to lose control. Transmission jumps are very harmful and timely measures must be taken to prevent accidents.
(1) Analysis of the cause of transmission jumps. Small excavators mostly use a mechanical shifting transmission mechanism. This transmission mechanism relies on the sliding gear sleeve to move axially on the fixed gear sleeve r and mesh with the driven gears of each gear to achieve gear shifting. During frequent gear shifting, the gear end faces of the above-mentioned meshing gears are easily worn into a cone, causing their meshing performance to decrease and cause jumps. Sudden changes in external loads can cause the transmission to jump. When the road surface is uneven, the machine is driving downhill or the driving route is improper, causing a sudden change in external load, this sudden change in load will act on the gear meshing gear of the transmission through the wheels and the drive shaft, causing the gear meshing gear to generate axial thrust and disengage, causing the transmission to jump. When a small excavator is driving on a slope, improper operation may also cause the transmission to jump gears.
(2) Handling of gear jumps during the working process. When driving on a flat road, the machine can be stopped according to the normal shutdown method, and the original field can be carefully found to eliminate the fault: when driving uphill, the gear position can be set to the low speed position or the 1st gear position, and the machine can be stopped when it reaches the top of the slope to eliminate the fault; if the downshift is unsuccessful or the gear jump occurs again, the machine should be stopped according to the slope shutdown action and requirements, and then the fault should be eliminated; when driving downhill, the gear position should be set to the high speed position or the gear grabbing (emergency gear) measures should be taken according to the gear upshift action, and the machine should be stopped for inspection after it reaches the bottom of the slope to eliminate the fault; if the gear upshift is unsuccessful or the gear jump occurs once (at this time, it is the home gear), the driver can control the engine speed at medium speed (to prevent the engine from stalling), use the chopping method to slide the machine to the bottom of the slope, and then eliminate the fault. If the gear shifting or grabbing fails or the gear jump occurs again (at this time, it is neutral), and the machine is on a steep slope (at this time, the machine will dive to the bottom of the slope at a very fast speed), it should be stopped quickly according to the downhill parking instructions and requirements, and then the fault should be eliminated.
(3) Preventive measures for transmission gear jump. Strictly follow the operating procedures and driving instructions to operate, try to avoid gear knocking during gear shifting to reduce the wear of the gear pair; strictly implement the maintenance system and strengthen the maintenance of the gear shifting device. When the gear shifting device rod system is not properly connected, it should be repaired in time to ensure that the gear shifting device performs well; pay attention to the repair and maintenance of the self-locking mechanism, and repair or replace the positioning steel balls, springs and shift fork shafts that have reduced or lost their positioning efficiency in time to ensure that the self-locking performance of the self-locking mechanism is in good condition; when assembling the transmission, it should be operated strictly according to the operating procedures to ensure that the various parts of the transmission are adjusted correctly and tightened appropriately. When driving on a large downhill road, the driver should strictly follow the downhill action instructions to operate, and must not operate in violation of regulations.
Fault analysis and treatment of small excavators
3. The boom cannot be lifted with load
(1) Fault reason. The boom of a small excavator cannot be lifted with load. Generally speaking, the main reason is that the main components of its hydraulic system are seriously worn. For example, the hydraulic pump is seriously worn, and the pump leaks seriously when running at high speed; the pump pressure is slightly increased when running at high speed, but due to the wear and leakage of the pump, the volumetric efficiency is significantly reduced, and it is difficult to reach the rated pressure. The long-term operation of the hydraulic pump aggravates the wear and the oil temperature rises, which causes the wear of hydraulic components and the aging and damage of seals, loss of sealing ability, and deterioration of hydraulic oil, leading to the occurrence of faults.
(2) Fault finding and repair. The first is to check the internal leakage of the boom cylinder. The simplest way is to raise the boom to see if it has obvious free fall. If the fall is obvious, disassemble the cylinder for inspection. If the seal is worn, it should be replaced; the second is to check the control valve. First, clean the safety valve and check whether the valve core is worn. If it is worn, it should be replaced. If there is still no change after the safety valve is installed, check the wear of the control valve core. The clearance limit is generally 0.06mm. If it is seriously worn, it should be replaced. Measure the pressure of the hydraulic pump. If the pressure is low, adjust it. If the pressure cannot be adjusted, it means that the hydraulic pump is seriously worn.
4. The boom is lifted slowly and weakly
The boom of the hydraulic small excavator moves slowly, and the rest of the movements are normal. Common reasons are that the pressure of the two pumps supplying hydraulic oil to the boom is too low; the set pressure of the main control valve of the boom is too low; the boom operating valve is stuck and cannot be fully opened; the seal of the boom cylinder is damaged, and the internal or external leakage is serious.
(1) Internal leakage distribution valve leakage. The main reasons for internal leakage are: the main valve core of the total safety valve is stuck, the clearance between the valve stem and the valve body is too large, the pressure regulating spring is damaged, the seal inside the valve is damaged, or there are sand holes in the valve body, etc. Disassemble and inspect whether the cone valve of the main safety valve is stuck and clean it: Check the matching clearance between the valve stem and the valve body. The normal matching clearance should be between 0.005 and 0.012 mm. If the covering clearance exceeds the tolerance, it should be chrome-plated and ground; check the pressure spring to see if the seal inside the valve is damaged; check whether the valve body has casting defects such as sand holes.
(2) Piston seal ring damage and gear pump wear. Damage to the piston seal ring of the boom hydraulic cylinder causes internal leakage. When the boom cylinder piston is retracted to the bottom, remove the rodless cavity oil pipe and continue to fill the boom cylinder with oil. If a large amount of working oil leaks out of the rodless cavity oil port, it means that the piston seal ring is damaged and should be replaced immediately. Disassemble and inspect the gear pump end face clearance, gear meshing clearance, radial clearance between the gear and the pump body, and internal seals of the gear pump to see if they are normal. Impurities in the hydraulic oil are the main cause of the grinding of the gear pump side plate. Blockage of the oil suction line and the oil filter will also cause the system pressure to drop, causing the boom to lift slowly and weakly.
(3) Leakage of the boom hydraulic cylinder. Check whether the valve core of the operating valve moves flexibly within the stroke. If the valve core is stuck or the oil leaks here, clean the valve or replace the seal at this part. If the fault still cannot be eliminated, finally disassemble and inspect the boom hydraulic cylinder, replace the seal, solve the problem of internal or external leakage of the hydraulic cylinder, and the fault can be eliminated.
(4) Oil overflows from the gearbox breather. The oil seal of the corresponding pump should be replaced in time, and the fault should be eliminated at one time when the machine is shut down for maintenance. Otherwise, repeated maintenance will inevitably waste a lot of lubricating oil and repair time. The maintenance process of hydraulic components must be kept clean and hygienic. After the fault is eliminated, first check the gear oil and hydraulic oil levels, and add them if they are insufficient. The engine must be started after opening the hydraulic oil tank switch valve, otherwise the gearbox or main pump may be damaged or even scrapped due to lack of oil. When troubleshooting the hydraulic system, the engine should be turned off first.
Fault analysis and treatment of small excavators
5 Unable to rotate and the rotation angle is too large When the small excavator is working, other working devices operate normally, but the upper body cannot rotate. The rotation failure of the upper body of a small excavator is related to the main pump, self-pressure reducing valve, swing operating handle, swing lock switch, swing lock solenoid valve, swing motor, swing reducer, swing bearing, etc. Fault detection should be analyzed and eliminated one by one according to the principle of simple to complex.
(1) Check the swing solenoid valve control oil circuit. If only the upper body cannot rotate and other working devices operate normally, it means that the main pump and self-pressure reducing valve are not faulty. If the swing reducer or swing support fails, there will definitely be abnormal noise or vibration. If there is abnormal noise or vibration, it may be a problem with the swing reducer or swing support. Check whether the swing control pressure value is within the normal range. Then check the swing main valve core. The main valve core should move flexibly in the valve body without sticking, which means that the main oil circuit can smoothly reach the swing motor. Check the swing lock switch and measure the voltage at both ends of the switch and the resistance of the swing lock solenoid valve coil to see if the voltage or resistance is normal. If it is normal, connect a three-way joint at the outlet of the swing solenoid valve control oil circuit and connect a 4MPa pressure gauge, operate the small excavator to swing, if the pressure here is too low, it means that the oil pressure flowing to release the brake is too low, the brake cannot be removed, and the small excavator cannot swing. If there is a fault, the valve core should be removed, the components should be cleaned, and the test run after reinstallation can eliminate the fault.
(2) Brake return oil circuit inspection. When the small excavator swing operation is completed and the operating handle is in the middle position, the small excavator swings too far under the action of inertia and cannot stop at the predetermined position. This phenomenon is mostly caused by untimely swing braking or insufficient braking force. It is related to the oil pressure for releasing the brake and components such as the swing locking solenoid valve, swing brake pads and brake seals. When checking the brake oil return line, it was found that there were colloidal particles in the throttle hole of the oil return line. Although the throttle hole was not completely blocked, it caused the oil return to be too slow, which delayed the time for the brake part to take effect, so that the slippage (i.e. the rotation angle) when the upper part stopped rotating was too large. Clean all components, especially the throttle hole and small oil channel. After installing all components and testing the machine, the rotation slippage can be within the specified range, and the fault can be eliminated.
multifunctional skid loader，Multifunctional skid steer loader attachments，Skid Steer Loader Attachments
Choose DIG-DOG for high-quality, customizable brush cutters for skid steers with fast delivery. Contact us today to discover how our superior products can enhance your land management tasks!
for more info just visit our website at www.dig-dog.com
contact # : +86 158 6218 2088
email : sales@bonovogroup.com