Construction machinery such as loaders are special vehicles. Operators should receive training and guidance from the manufacturer, have a full understanding of the structure and performance of the machine, and gain certain operation and maintenance experience before operating the machine. Therefore, understanding some common fault maintenance knowledge of loaders is beneficial to daily loader operation and maintenance. Let’s take a look at the common fault analysis of loaders and the complete knowledge of loader maintenance.
Common fault analysis of loaders, complete knowledge of loader maintenance
1. The loader is weak or does not move in a certain gear, and the other gears are normal.
Key points for judgment:
When the loader does not move or moves slowly, the main drive shaft rotates quickly and powerfully. When the engine speed is increased, the increase in the speed of the main drive shaft is obviously disproportionate to the front and rear drive shafts.
The oil pressure of the neutral gear and the other gears is normal, and the pressure drops significantly after the gear is engaged.
Cause of the fault:
1) The bearing cover or nylon ring is severely worn.
2) If the bearing cover or nylon ring is good or slightly worn, it is confirmed that the inner and outer seal rings of the clutch in this gear are not sealed properly.
Troubleshooting method:
Replace the corresponding damaged parts, i.e. the bearing cover or nylon ring, inner and outer sealing rings, and readjust the clearance between the sleeve and the bearing cover.
Fault analysis: If a certain gear is weak or does not move, the torque converter, travel pump, pressure reducing valve and other common oil circuits and components of each gear can be eliminated. The fault can only occur in the oil circuit between the speed control valve and the clutch piston of the gear. After the bearing cover, nylon ring, inner and outer sealing rings and other weak parts are worn, the oil supplied to the clutch piston cavity leaks a lot from the worn parts, resulting in a decrease in oil pressure. The oil pressure is normal when the neutral gear or other gears are engaged because the oil does not flow through the worn parts.
2. The machine moves forward automatically in neutral gear, and it can also drive normally when the forward gear is engaged. When the reverse gear is engaged, the machine stops and cannot move. The working pressure of each gear is normal.
Cause of failure:
Forward clutch master and slave plates are sintered and locked
Forward clutch piston is stuck and support check valve is blocked
Troubleshooting method:
Disassemble the forward clutch, clean the oil channel, replace the master and slave friction plates and related damaged parts, clean all related parts, replace the outer sealing ring, clean and clear the check valve, replace the clutch friction plate, inner and outer sealing rings
3. During the normal driving of the whole machine, it suddenly stops working after the second gear is engaged. Check that the working pressure of this gear and the remaining gears are normal.
Cause of failure:
The clutch shaft of this gear is broken
Troubleshooting method:
Replace the clutch shaft and readjust the bearing clearance
4. The whole machine suddenly stops moving forward or backward during driving, and the speed change working pressure is normal.
Cause of failure:
1). Speed distribution valve failure or (40F, 50D, 50F) accumulator damage, speed valve air control valve stem stuck or damaged
2). Oil inlet blocked
3). Accumulator oil circuit blocked
4). Air control stop valve failure
Troubleshooting:
Clean the speed valve isolation valve stem or replace the air control valve to dredge the relevant oil circuits, repair or replace the air control stop valve
5. The whole machine works normally, but suddenly there is no steering, no lifting, and no movement, which means the elastic connecting plate is damaged or the connecting wheel is toothed
Cause of failure:
The elastic connecting plate is broken, the fixing bolts of the elastic connecting plate are damaged, and the connecting wheel is toothed
Troubleshooting:
Replace the elastic connecting plate and the connecting wheel
6. The speed working pressure is normal. When the whole machine is under heavy load, the main drive shaft rotates quickly and powerfully. The whole machine cannot work normally during excavation and there is metallurgical powder in the transmission oil
Cause of failure:
The high and low speed lever is not in the low speed position for reversing or the speed change valve is not in place, the 1:3 clutch is damaged, and the forward clutch is damaged
Troubleshooting method:
Hang the high and low speed lever to the low speed position and readjust the pull rod
Replace the clutch friction plate and damaged related parts
7. Oil leakage from the top breather of the torque converter
Cause of failure:
The valve stem of the air control valve of the speed change valve is “O”, air leakage, the return oil filter of the torque converter is blocked, the internal oil circuit of the torque converter or the guide wheel seat oil circuit is blocked, and the return oil pipeline from the torque converter to the gearbox is blocked
Troubleshooting method:
Replace the “O” ring of the air control valve, clean the return oil filter or replace the filter element, clean each oil circuit or replace the guide wheel seat, clean or replace Replace the oil pipe
8. The torque converter has abnormal noise
Cause of the fault:
The torque converter connecting teeth are broken or the rubber teeth are damaged, the elastic connecting plate of the torque converter is disassembled, the main and passive gear shafts or bearings of 30F and 30D torque converters are damaged, the main drive shaft splines do not correspond or the universal joint bearing clearance is large
Troubleshooting method:
Replace the connecting wheel or rubber teeth, replace the elastic connecting plate, replace the main and passive gears or bearings, readjust or adjust the clearance
9. The whole machine works normally, the oil temperature is high, the output power is insufficient and there is aluminum foam in the transmission oil
Cause of the fault:
The return oil filter is blocked, the mechanical oil radiator is blocked, the return oil pipeline is blocked, the bearing is damaged, and the three wheels of the torque converter are worn
Troubleshooting method:
Clean the filter element or replace the filter element, replace the radiator, clean and dredge the oil circuits or replace them, Replace bearings, replace three wheels and adjust clearance
10. Low speed or high speed gear disengagement
Fault cause:
The clearance of the operating part is too large or the pull rod is improperly adjusted, the sleeve and high and low speed gears are worn, the meshing amount is too small, the clearance between the high and low speed gear bushing and the output shaft is too large, the shift fork is deformed or the shift fork shaft positioning spring is broken
Troubleshooting method:
Adjust the clearance of each related pull rod, replace the damaged sleeve and gear, replace the gear bushing and adjust the clearance, replace or repair the shift fork replacement spring
11. The hydraulic oil in the gearbox increases, and the hydraulic oil in the working hydraulic oil tank decreases
Fault cause:
The working pump or steering pump oil seal is aging, the axial clearance or radial clearance of the working pump or steering pump shaft is too large
Troubleshooting method:
Replace the working pump or steering pump oil seal, repair and check the oil pump or Replace the oil pump
12. The hydraulic oil in the gearbox is reduced, and the hydraulic oil in the working hydraulic oil tank is increased
Cause of the fault:
The oil inlet filter of the working oil tank is blocked or the oil pump suction pipe is blocked
Troubleshooting method:
Clean or replace the oil inlet filter, replace the oil pump suction pipe
13. After the gearbox is in neutral or in gear, the speed change pressure is low and the whole machine is powerless to move
Cause of the fault:
Insufficient transmission oil in the gearbox, the filter of the gearbox oil pan is blocked, the travel pump is damaged, the volumetric efficiency is low, the pressure reducing valve or the inlet pressure valve is improperly adjusted, and the travel pump suction pipe is aged or seriously bent
Troubleshooting method:
Add enough hydraulic oil in the gearbox to the middle of the oil mark at idle speed, replace or clean the filter, replace the travel pump, readjust the pressure to the specified range, and replace the oil pipe.
14. The loader suddenly has no steering during normal driving, and the steering wheel can be easily turned at the same time.
Cause of failure:
Steering cylinder piston falls off
Steering column and steering gear connecting sleeve are broken or damaged
Troubleshooting method:
Replace the steering cylinder,
15. The loader suddenly stops steering during normal driving, and the steering wheel cannot be turned.
Troubleshooting method:
Steering pump roller key or connecting sleeve spline is damaged,
Steering gear check valve falls off (inside the valve block) Ф8mn steel ball (check valve) in the steering gear fails,
Replace the steering pump or connecting sleeve, replace the valve block or check valve
16. Automatic steering, the steering wheel cannot automatically return to the center position.
Cause of failure:
The return spring sheet in the steering gear is broken
Troubleshooting method:
Replace the return spring sheet or the steering gear assembly
17. When the steering wheel encounters uneven ground, the direction automatically deviates to the concave side of the ground
Damage of the two-way overload buffer valve
Troubleshooting method:
Replace the steering gear, clean and repair or replace the valve block
18. Heavy steering
Cause of failure:
The oil filter or oil pipe of the steering pump is blocked, the gap between the steering column and the steering gear is small or there is no gap, the steering gear valve core and valve sleeve, stator and rotor are too tight, the monostable valve or overflow adjustment pressure is low or stuck, and the steering pump volumetric efficiency is low
Troubleshooting method:
Clean the filter element or replace the oil pipe, adjust its gap, replace the steering gear or clean and grind, adjust its pressure to the specified value, replace the oil Pump
19. Steering without end feeling
Cause of failure:
The spring of the two-way buffer valve on the steering gear valve block is broken or the adjustment pressure of the two-way buffer valve is lower than the pressure of the steering safety valve, the refueling line of the steering safety valve is blocked, the clearance of the steering gear valve body, valve sleeve, valve core or stator pair is seriously worn and the clearance is too large
Troubleshooting method:
Replace the spring or adjust its pressure to the specified value, clean and dredge the pipeline, and replace the steering gear
20.50F loader suddenly has no lifting and no steering during work
Cause of failure:
The pilot pump roller key or pilot pump shaft is broken, and the bearing at the connection between the torque converter and the pilot pump is damaged
Troubleshooting method:
Replace the pilot pump or # shaft key matching septum, replace the bearing
21. The steering wheel turns but the steering action is very slow, the steering wheel turns lightly, and the number of revolutions is Increased
Cause of failure:
Steering cylinder piston seal damaged
Two-way overload buffer damaged
The wear clearance between the rotor and the stator is too large, and the steering pump efficiency is low
22. When the loader turns, there is an abnormal sound on the front or rear axle, and the sound disappears when driving in a straight line
Cause of failure:
Differential planetary gears and half-axle gears are not matched or meshed poorly, differential planetary gears are toothed or surface damaged, planetary gears and differential cross shafts are stuck or the clearance is poorly adjusted
Troubleshooting method:
Replace planetary gears or cross shaft gears, adjust the clearance or replace gears
23. The loader driving axle has noise, which does not disappear when sliding
Cause of failure:
Insufficient lubricating oil in the drive axle housing, the meshing clearance between the main and driven spiral bevel gears is too small, and the differential housing and the cross shaft are not properly adjusted. The clearance of the planetary gear of the axis is too large
Troubleshooting method:
Add enough lubricating oil according to the standard, and adjust the clearance to the specified value
24. Fault phenomenon: The front and rear axles suddenly have no drive during driving
Fault cause:
The half-axle is broken
Troubleshooting method:
Replace the half-axle
25. The loader is driving normally, and the four wheels produce abnormal noises
Fault cause:
The wheel side taper roller bearing is damaged, the planetary wheel shaft needle bearing is damaged, the sun gear and planetary gear are broken and damaged, the inner gear ring is broken, and the bolts connecting the inner gear ring and the inner gear ring support frame are broken
Troubleshooting method: Replace the bearing, adjust its clearance, replace the needle bearing, replace the sun gear and planetary gear, replace the inner gear ring, and replace its bolts Ф10×75
26. The boom suddenly does not lift, does not retract, and does not tip.
Fault cause:
The main safety valve of the work distribution valve is stuck.
Handling method:
Open the main safety valve for cleaning, and pay special attention not to loosen the pressure regulating nut at the rear end of the safety valve.
Fault analysis:
After the safety valve is stuck, the oil of the working pump flows into the return oil circuit, and the lifting cylinder and dump cylinder oil circuit cannot build up the required working pressure, resulting in the corresponding boom and bucket not moving. This type of fault is generally caused by poor cleanliness of the hydraulic system. For machines that have been used for a long time, the hydraulic oil and oil suction filter should be fully inspected or replaced.
27. Fault phenomenon:
1) The lifting speed is normal for light loads, but it suddenly stops lifting or lifts very slowly after exceeding a certain weight. The fault phenomenon of hot and cold vehicles is basically the same.
2) It can lift, but cannot reach the maximum lifting height.
Cause of fault:
1) Overload
2) The set pressure of the main safety valve of the working distribution valve becomes low.
Treatment method:
1. Eliminate overload.
Overload can cause early damage to the main safety valve and working pump!
2. Clean the main safety valve and recalibrate the pressure.
Note: The set pressure must meet the requirements of the manual. If the set pressure is too high, it may cause serious damage to the working pump, working valve and high-pressure oil pipe!
28. The bucket is normally retracted, but the boom is slowly lifted. The heavier the material is, the slower the lifting speed is. The fault is aggravated after the engine is warmed up.
Cause of the fault:
(1) Early wear of the piston seal of the lifting cylinder. Judgment method: Raise the boom to the highest position, disassemble the oil inlet joint of the piston rod cavity of one of the lifting cylinders, put the boom lever of the working distribution valve in the “lift” position, and step on the high-speed accelerator to observe the leakage at the lifting cylinder interface. Normally, there is a slight leakage. The same is true for the other lifting cylinder.
(2) The efficiency of the working pump is reduced. After excluding the first reason, it can be basically determined that the efficiency of the working pump is reduced.
Fault analysis:
The lifting speed of the boom is mainly determined by the speed and efficiency of the working pump and the leakage of the lifting oil circuit. If the seal of the lifting cylinder piston is damaged or the efficiency of the working pump decreases, the leakage will increase accordingly, and it will increase with the increase of working pressure, that is, the heavier the material, the slower the lifting.
29. The boom stops at a certain position and cannot stop but sinks
Cause of failure:
The seal on the lifting cylinder piston is damaged, and the clearance between the working distribution valve stem and the valve body is out of tolerance
Troubleshooting:
Replace the seal on the piston, and check the clearance between the valve stem and the valve rest. If the clearance is too large, the working distribution valve should be replaced
30. The loader is working normally, and the working hydraulic device (lifting, dumping) suddenly stops working at the same time
Cause of failure:
The working oil pump is damaged, the spline and the connecting sleeve keyway on the working oil pump are damaged, or the drive oil pump shaft is broken
Troubleshooting:
Replace the oil pump and replace the damaged parts
31. The operating lever of the working distribution valve (lifting link, boom link) cannot be positioned
Cause of failure:
Positioning sleeve is damaged Bad, positioning steel ball damaged, positioning spring broken
Troubleshooting method:
Replace the positioning sleeve, replace the positioning steel ball, replace the positioning spring
32. The bucket of the loader is unable to retract when working or automatically flips down after retracting the bucket and the bucket automatically retracts when there is resistance at the bottom of the bucket
Fault cause:
The seal in the bucket cylinder is damaged, the large cavity over-cut valve is stuck or damaged, and the small cavity overload valve is stuck or damaged
Troubleshooting method:
Replace the seal on the piston, clean or replace the corresponding parts
33. When the loader is working, the hydraulic system generates noise regardless of lifting or retracting the bucket
Fault cause:
There is less hydraulic oil in the working oil tank, the vacuum valve of the 30-type working hydraulic oil tank is damaged or not tightened, and the oil suction pipe of the working oil tank is aging The suction is flat, the clamp of the working device oil pipe is loose, the oil pump suction pipe is inhaled, and the main valve on the work distribution is not working properly.
Troubleshooting method:
Add enough hydraulic oil to reach its standard value, tighten or replace the vacuum valve, clean the filter element or replace the oil pipe, clean and repair the main safety valve, and replace the main safety valve if necessary.
34. When operating the lifting and dumping joint valve stems, oil leaks from the small hole at the rear of the positioning sleeve
Cause of failure:
The valve stem and the spring seat “O” ring are damaged
Troubleshooting method:
Replace the “O” ring and tighten it
35. Low brake pressure causes poor braking or no braking
Cause of failure:
Air compressor is damaged, pipeline leaks, compressed air pressure is insufficient, multi-function unloading valve is damaged or adjusted, and the pressure is low
Troubleshooting method ：
Check and replace the damaged parts or replace the assembly, check and tighten the leaking parts, repair the unloading valve or adjust the pressure to its standard value
36. The brake air pressure is normal, but the braking effect is poor or there is no braking
Cause of failure:
The leather cup of the brake chamber is damaged or the air control stop valve is damaged, the brake valve exhausts less, and the brake hub and brake pad wear is too large
Troubleshooting method:
Replace the leather cup or air control stop valve, adjust its clearance or replace the brake valve, replace the damaged parts
37. There is an abnormal sound when braking
Cause of failure:
The hardness of the brake shoe friction plate is too large or the rivet is exposed, there are metal debris between the brake hub and the friction plate, the brake is overheated and the friction plate surface is hardened
Troubleshooting method
Eliminate the above phenomenon
38. When braking, it deflects to one side
Cause of the fault:
The gap between the two front wheel brake discs and the friction pads is different, the contact area of the two front wheel friction pads is different, there is air in a front wheel piston, a front wheel brake caliper is deformed, the air pressure of the two front wheels is inconsistent, and the friction pad of a side wheel is wet with oil and water
Troubleshooting method:
Check the brake disc and friction pads, if damaged, replace them, check and replace the friction pads, and drain them according to the correct method
Air, replace, the air pressure in the inflation chamber is specified and the air pressure is consistent, clean and blow dry
39. The brake pedal is stepped to the bottom during driving, and the brake suddenly fails
Fault cause:
The seal ring of the booster master cylinder is damaged or overturned, there is no brake fluid in the booster master cylinder, there is no brake air pressure, the brake pipeline is severely ruptured or the pipeline joint is disconnected
Troubleshooting method:
Replace the damaged seal, add enough brake fluid to reach the standard value, exhaust the air in the oil circuit, and replace the damaged brake pipeline
40. During continuous driving, the brake disc is seriously heated. After releasing the brake pedal, the loader has difficulty starting and the brake caliper piston does not return to its position
Fault cause:
The loader brake pedal has no free travel or poor return, the booster seal is expanded or the piston is deformed or the piston is stuck by dirt, the booster return spring is broken, the rectangular ring on the brake caliper piston is damaged or the piston is stuck or rusted, and there is a gap between the brake disc and the friction plate The gap is too small, the brake pipe is concave and blocked, the oil return is not smooth, the brake fluid viscosity is too high or too dirty, making it difficult to return oil, and the brake valve cannot be exhausted instantly
Troubleshooting method:
Adjust its gap to the normal value, clean or replace the damaged parts, replace the return spring, clean or replace the rectangular ring piston, adjust its gap or replace the friction plate with a thinner one, replace and dredge the oil circuits, clean the booster pump or replace the uniform type of brake oil, replace the brake valve or high speed its gap
41. After the manual brake valve is connected, it is easy to pop out
Cause of failure:
The air pressure is too low to reach 0.35MPa, the manual brake valve is damaged and the seal is not tight, the air control stop valve is damaged, and the seal on the parking station air chamber piston is damaged
Troubleshooting method:
Check whether the air compressor is working to see if there is any leakage in the pipeline, and replace the damaged seal
42. After turning on the start switch, the starter does not turn
Cause of failure Cause:
Starter damaged, poor contact of starter switch knob, loose wire joint, insufficient battery charge, electromagnetic switch contacts not in contact or burned
Troubleshooting:
Repair or replace starter, repair or replace starter switch, check and tighten connecting wires and charge, repair or replace electromagnetic switch
43. After turning on the starter switch, the starter idles and cannot drive the engine to run
Fault cause: The electromagnetic switch core stroke is too short, the armature moves or the auxiliary coil is short-circuited or open-circuited, the one-way clutch slips, and the flywheel teeth are severely worn or broken
Troubleshooting: Check and repair the electromagnetic switch or replace it, repair or replace the coil, and replace the flywheel
44. The engine is idling or running at high speed, and the ammeter indicates no charging
Fault cause:
The generator armature and field wiring insulators are damaged, the slip ring insulation is broken down, the silicon diode is broken down, short-circuited or broken circuit, voltage regulator contacts burnt out, stator or rotor coil grounded or broken
Troubleshooting methods:
Check and repair damaged parts, replace slip rings, replace diodes, replace regulators, repair stator or rotor coils
45. After turning on the starter switch, only the starter motor makes a “snap” sound, but cannot rotate
Fault cause:
Battery power is insufficient or the starter circuit wire is loose, starter bearing is damaged, armature shaft is bent (rotor part) collides (stator part), armature and magnetic field coil are short-circuited
Troubleshooting methods:
Fully charge the battery and tighten the wire connection, replace bearings or starter, check and repair armature shaft or replace starter, check and repair coil or replace, replace starter switch or electromagnetic switch
46. Poor cooling effect or no cooling
Fault cause:
Electromagnetic clutch is not closed or compressor belt is too loose, refrigerant is insufficient, cold Condenser fan or blower does not rotate, intake pipe is blocked
Troubleshooting method:
Check whether the electromagnetic clutch is damaged, adjust the belt, loader sales 18504725773 add refrigerant to its standard value, check the fan or line, check the intake pipe to remove the blockage
47. The air conditioning system is noisy
Failure cause:
The transmission belt is too loose or severely worn, the compressor mounting bracket is loose, the blower motor is loose or worn, the electromagnetic clutch slips and makes noise, and the internal parts of the compressor are worn
Troubleshooting method:
Adjust the belt or replace it, tighten the loose parts and readjust them, replace the motor or repair it, check and repair the electromagnetic clutch or replace it, replace the damaged parts, and replace the compressor if necessary
48. There is a “pop” exhaust sound around the cylinder head during engine operation, and water returns at the water filling hole of the water tank and intensifies with the increase of engine speed
So Cause of failure:
The cylinder head is deformed due to uneven tightening torque of fixed bolts, cylinder head quality problems, and early injection advance angle
Troubleshooting method:
Re-adjust according to the specified torque and in order, replace the cylinder head, replace the cylinder head with a good quality one, and adjust the advance angle
49. Drain the oil from the oil filling port and the oil dipstick
Cause of failure:
The oil level in the oil pan is too high, and the air pressure in the oil pan is too high (the oil temperature is too high, the oil-water separator is blocked or the crankcase ventilation hole is blocked, and the piston ring of individual cylinders is not matched, the piston ring and cylinder liner are seriously worn and the seal is poor, so that high-pressure gas enters the oil bottom)
50. High engine oil consumption
Cause of failure:
Oil leakage, supercharger oil leakage, air filter blockage, excessive oil filling, oil brand does not meet the requirements, ordinary oil viscosity is too low, oil-gas separator is blocked, air compressor The piston, piston ring and cylinder wall are seriously worn, and the cylinder liner is worn and blowby at an early stage
Troubleshooting method:
Replace the oil seal or tighten the oil leakage part, replace the supercharger, clean the filter element, put it in the specified position, replace the specified engine oil, clean or replace, replace the piston ring, piston ring and cylinder wall, replace the cylinder liner and other parts
51. The engine oil is mixed with water, and the color of the engine oil turns white
Cause of failure:
The water plug is not pressed tightly, resulting in loose leakage or water plug rot, cylinder gasket damage or cylinder head crack, the body has sand holes, the engine oil cooler is cracked or welded
Troubleshooting method:
Replace the water plug, replace the cylinder gasket or cylinder head, replace the body, check and repair or replace the oil cooler
52. Diesel is mixed in the engine oil and the oil level rises
Cause of failure:
The needle valve of a cylinder injector is damaged, the cracked oil head is burned, etc., diesel leaks inside the high-pressure pump, and the oil pump Piston seal ring is damaged
Troubleshooting method:
Check, repair or replace the oil cooler, check and calibrate the injector or replace it, replace or repair the high-pressure oil pump, replace the oil pump
53. The engine emits black smoke, and the smoke increases with the increase of engine speed
Failure cause:
Excessive and uneven injection or poor atomization, insufficient cylinder pressure, incomplete combustion, oil entering the combustion chamber, poor diesel quality
Troubleshooting method:
Clean the air filter element to ensure the correct valve timing, high-speed injection pump fuel supply advance angle, piston, piston ring, cylinder sleeve are seriously worn, the injector should be replaced, if the valve is not closed tightly, it should be ground, check the oil-water separator and supercharger, if it is blocked or damaged, it should be replaced, replace the diesel with the grade that meets the requirements, and operate correctly. If the accelerator is stepped on suddenly, black smoke will also appear
54. When the ZL50C loader is in idle state, the boom descends and lifts slowly.
Accompanying phenomenon: When the working time is long, the working hydraulic system heats up more seriously.
Cause of the fault:
The pilot pump relief valve has a low set pressure
The pilot pump relief valve core is stuck or the spring is broken
The pilot pump efficiency is reduced.
Troubleshooting method
Re-adjust the pressure to the calibrated value of 2.5Mpa
Replace the pilot pump relief valve
Replace the pilot pump
Fault analysis:
The direct reason for the reduction in the lifting and lowering speed of the loader boom is the decrease in the oil flow supplied to the lifting cylinder. The reasons for the low flow of the cylinder are: the efficiency of the working pump decreases, the actual oil supply decreases, the opening of the working valve stem becomes smaller, and the leakage point exists. The above fault has the problem of slow action in both the lifting and lowering states, so the first and third reasons can be excluded. The reason for the reduction in the opening of the working valve stem is the processing deviation between the valve stem and the valve body. Therefore, this fault exists at the factory, and with the improvement of processing accuracy, this problem is becoming less and less. The second reason is that the pilot pressure is too low, causing the valve stem to not be pushed to the specified position. In actual measurement, it is found that when the pilot pressure is reduced to 13kgf/cm2, the idling speed will slow down to about 17 seconds. In actual maintenance, the overflow valve on the pilot pump should be removed first to observe whether its valve core and return spring are damaged. If normal, clean and readjust the pressure. If the adjustment effect is not obvious, it is caused by the reduced efficiency of the pilot pump, and the pilot pump can only be replaced. In addition, due to the decrease in the oil flow capacity of the valve stem, the throttling loss at the valve port will directly lead to an increase in the system oil temperature. When this fault occurs, it is generally not obvious when lifting because it is generally working at medium and high speed throttle and the pump supplies a large amount of oil. However, when descending, it is generally at low throttle or idle speed, and the system oil supply is reduced, so the descent speed will be significantly slowed down. This should be paid special attention to during inspection.
