Inspection methods, procedures and precautions for excavators
The excavator is an indispensable and highly efficient earth-moving machinery in large-scale infrastructure construction, open-pit mining spoil removal, and agricultural water conservancy renovation projects. It integrates functions of loading, transportation, soil unloading, spreading and initial compaction. A single operation can complete the entire soil transportation process from the excavation area to the filling area. Its core technical features lie in the large-capacity bucket, the forced soil unloading mechanism (push plate type or flipping type), and the high maneuverability chassis suitable for long-distance and high-speed transfer. The operating load of the loader is extremely high. The bucket bears intense impact when cutting the soil, and the unloading mechanism frequently reciprocates under heavy load. The hydraulic and transmission systems operate at full load for a long time. Any excessive wear of the bucket edge, stuck push plate, failure of the articulated steering, or leakage of the hydraulic system will lead to a sudden drop in equipment efficiency, a sharp increase in fuel consumption, and even structural component fractures. In scenarios such as new machine delivery, second-hand equipment transactions, factory acceptance for major overhauls, and asset inventory of engineering projects, a comprehensive inspection covering the bucket assembly, unloading mechanism, hydraulic and transmission system, articulated steering, and safety protection is a core means for accurately determining the equipment's operational capacity and remaining economic life.
I. Overview of Inspection Methods
Based on the power type of the loader (single engine/double engine), the traveling mechanism (wheeled/track-type), the bucket capacity, the soil-discharging method (forced push plate discharging/tilt discharging), and the client's requirements, the inspection usually employs the following methods in combination:
Static comprehensive inspection: The equipment is left to stand still. A detailed visual inspection, measurement with measuring tools, and non-destructive testing are conducted on the main frame, articulated system, bucket assembly, bucket door mechanism, earth-discharging push plate, hydraulic cylinder, transmission shaft, gearbox, drive axle, tires, cab, and electrical system, etc., item by item.
Dynamic performance test: On a safe site or construction access road, verify the engine performance, smooth shifting, flexible articulated steering, the coordination and speed of bucket lifting and flipping actions, as well as the opening and closing of the bucket door and the operation of the earth-discharging push plate.
Special test for earth-moving with a loader: On the soil operation area where conditions permit, conduct a full-process test covering short-distance loading, transportation, unloading, and spreading. Measure the performance of the bucket entering the soil, the full-bucket rate, the flatness of the unloading, and the thermal balance state of the hydraulic system.
Hydraulic system pressure and pressure retention test: Conduct pressure and overflow pressure tests for each working circuit. Perform pressure retention settlement tests on the bucket lifting cylinder, bucket door cylinder, and earth-discharging cylinder.
Document and nameplate traceability: Verify the consistency between the entire machine nameplate, engine nameplate, transmission nameplate, bucket nameplate, hydraulic main pump nameplate and the factory documents, as well as the major overhaul records.
The third-party inspection consists of a complete package including "static full inspection + dynamic performance test + special test for bucket loading and unloading + in-depth inspection of hydraulic system". For high-value transactions or major disputes, additional tests such as thickness measurement of the bucket edge and oil spectrum analysis must be conducted.
II. Inspection Process
1. Data Collection and Preparation for Inspection
The client provides a list of the machines to be inspected, clearly stating the manufacturer, model, bucket capacity (stacking/flat loading), power type (single engine/double engine), soil removal method, rated power, working weight, factory serial number, working hours, applicable standards (such as GB/T 25685, JB/T 10756, etc.). The inspector prepares: tape measure, laser rangefinder, ultrasonic thickness gauge, vernier caliper, feeler gauge, hydraulic pressure gauge set, infrared thermometer, noise meter, oil sample bottle, walkie-talkie, etc.
2. Confirmation of venue and safety conditions
The dynamic testing site should be a solid and flat hard surface or a dedicated test track. For the bucket loading test, a soil operation area needs to be prepared. An isolation warning line should be set up in the testing area, and non-inspection personnel are prohibited from entering. Inspectors should wear safety helmets, reflective vests, and anti-shatter shoes. When inspecting under the bucket or inside the soil unloading mechanism, it is necessary to confirm that the engine has been turned off, the bucket is reliably mechanically supported, and all hydraulic cylinders have been locked or depressurized.
3. Identity and Label Verification
Machine nameplate: Verify the manufacturer, model, factory serial number, manufacturing date, bucket capacity, rated power, working weight, etc.
Engine nameplate (single engine / front and rear engines): Check the model, serial number, power one by one, and compare them with the overall nameplate and the major overhaul record.
Transmission/Drive Coupling Nameplate: Record the model and serial number to confirm it is an original factory component.
Hydraulic main pump nameplate: Record the model and serial number.
Bucket nameplate: Records the bucket model, capacity, and factory serial number. Any absence of the nameplate or mismatch of information should be immediately upgraded to a serious non-conformity item.
4. Inspection of the main frame and the articulation system - The core of load-bearing and steering
The loader adopts a front and rear frame hinged structure. The bucket is located between the front and rear axles. The hinge point not only bears the steering force, but also withstands the huge bending moments and torques during loading and transportation.
Front frame: Use a strong flashlight for close inspection. Key areas: Weld seams of the bucket coupling ear seat, weld seams of the lifting cylinder support, welding area of the articulated seat, and front axle mounting seat.
Rear frame: Focus on inspecting the hinged seat, the transmission/engine support beam, the rear axle housing connection area, and the welds of the weight block mounting seat.
Hinge system: The axial and radial clearances of the upper and lower hinge pin shafts are precisely measured using a dial indicator or a feeler gauge. Hinge points with excessive clearances will cause vehicle swaying and inaccurate bucket positioning. The hinge bearing housing has no cracks and the dust-proof sealing ring is intact. Inspection of the gap between the hinge steering cylinder ear seat.
Rack straightness: By visually inspecting on a flat surface whether the front and rear racks are on the same longitudinal axis, and checking if there is any permanent skew at the hinge points due to overload or collision.
5. Depth Inspection of the Bucket Assembly - Core Working Device
The bucket is the most valuable and wear-prone component of a loader.
Bucket cutting edge and bottom plate: Use an ultrasonic thickness gauge to measure the wall thickness of the bucket bottom plate, side plates, and rear wall. Focus on inspecting the area of the bucket cutting edge - this is the frontmost part where soil is cut, and the wear is the most severe. Check that the thickness of the cutting edge has decreased by more than 30% compared to the original specification. If the cutting edge thickness has decreased by more than 30%, the bucket's impact resistance will significantly decrease. Check each of the fixing bolts of the cutting edge for looseness or fracture.
Bucket teeth/blade: Measurement of the remaining tooth tip height of replaceable bucket teeth, inspection for cracks in the tooth seats. Sharpness of the integral blade - a blunt blade edge will significantly increase the cutting resistance.
Dunmen (Front Door): The oil cylinder for opening and closing the dunmen is free from leakage. The dunmen panel is undamaged and there are no cracks in the welds. When the dunmen is closed, the gap between it and the front opening of the bucket is measured using a feeler gauge - if the gap is too large, it will cause soil leakage during transportation.
Earth removal push plate / flipping mechanism:
Force-discharge soil push plate type: The push plate moves smoothly throughout its full travel within the bucket without any jamming. The gap between the push plate and the inner wall of the bucket is measured at multiple points using a feeler gauge. If the gap is too large, it will result in incomplete soil discharge and increased residual soil. The piston rod of the push plate cylinder is undamaged and there is no leakage in the seal.
Reversing earth-discharging type: The full stroke of the bucket flipping cylinder is smooth, and the flipping angle meets the standards. Inspection of the gap between the bucket flipping bearing seat and the pin shaft.
Bucket coupling and lifting mechanism: The clearance between the coupling pin and bushing of the bucket and the frame is measured using a feeler gauge. The clearance of the ear seat of the lifting cylinder is normal. The bucket lifting and lowering process is smooth throughout the entire range. The hydraulic lock function - after the bucket is lifted, the directional valve is closed, and the bucket should not significantly sink.
6. Inspection of Power Transmission System
Excavators are usually equipped with high-power diesel engines, with two engines in total - one at the front and one at the rear for the dual-engine models.
Engine: Start the front engine and the rear engine (if present) one by one. Check the cold and hot start performance, idle stability, acceleration response and exhaust smoke color. The power output is stable at full load (rated speed). Conduct an external leakage check. Condition of the air filter and pre-filter - the dust in the operating environment of the excavator is extremely high, and a clogged filter will lead to a decrease in power.
Transmission/Torque Converter: The housing shows no leakage. The transmission fluid level and quality are checked. The gear shifting is smooth for all gears (forward/reverse, high speed/low speed), without slipping, shock, or abnormal noise. For dual-engine models, the synchronization control function of the front and rear engines needs to be checked.
Transmission shaft: Check for looseness of the front and rear transmission shaft universal joints, and tighten the connecting bolts. The intermediate support bearings are in good condition.
Drive axle: There is no oil leakage in the front and rear drive axle housings, and the ventilation plugs are clean. The oil level of the wheel hub reducer is normal. The differential lock function verification (if any).
7. Hydraulic System Inspection - The Core of the Loader's Power
Hydraulic oil tank: The liquid level is within the scale range, the respirator is clean. The oil color is normal, without emulsification turning white, no discoloration, and no metallic reflection. If possible, take samples for testing.
Main hydraulic pump: The housing shows no leakage, and there is no abnormal noise during operation. The connecting pipes and joints show no leakage.
Multi-channel control valve assembly: The valve body connection surfaces show no oil leakage. Each control valve core operates flexibly and returns accurately. The functions of bucket lifting, bucket door opening and closing, and soil discharge push plate are all normal.
Hydraulic cylinders: Bucket lifting cylinder, bucket door cylinder, earth-discharging push plate cylinder (or flipping cylinder), articulated steering cylinder - Inspection of chromium plating on the piston rods of all cylinders, measurement of the gap between the ear seat pin shaft, and integrity of the dust-proof sealing rings. Pressure retention test (refer to the dynamic test section).
Piping and joints: For each individual hose of the entire machine, check for aging, cracking, and bulging. Focus on inspecting the interference and friction points between the hose and the frame, as well as the bucket. The hoses in the bucket area are exposed to harsh conditions of stone impact and soil abrasion, so they must be manually inspected one by one.
8. Inspection of the walking system and tires
Tires: The tires of the loader have large specifications and high levels, and can withstand extremely heavy loads. Check the depth of the tread pattern, cuts on the sidewall, and bulges on each wheel. Record any abnormal wear. Measure the tire pressure of each wheel using a heavy-duty tire pressure gauge and compare it with the nominal value. Insufficient tire pressure will cause the tires to overheat and peel off, which is the main cause of tire blowouts.
Wheels: No deformation, no cracks. Inspection of bolt torque.
Suspension system: The suspension cylinders of the front and rear axles (if equipped) or the coil springs. The suspension cylinders have no leakage, and the nitrogen pressure is normal (if equipped with a reservoir).
9. Electrical and Control System Inspection
Dashboard: The functions of various instruments such as engine speed at front and rear, water temperature, oil pressure, voltage, air pressure, and hour counter are all normal. The fault alarm indicator light passed the self-check.
Control device: The steering wheel, gearshift lever, bucket control lever, and hopper/unloading control lever operate flexibly without any jamming.
Lights and alarms: Front and rear working lights, marker lights, turn signals, brake lights, and reversing alarm functions are all functioning properly. During the operation of the loader, there is a significant amount of dust, and lights are a necessary safety feature.
Battery: The terminals are not corroded and the main power switch is functional.
10. Special verification of safety devices
ROPS/FOPS cab: The anti-rollover and anti-fall object protection structure is intact, without deformation, weld cracks, or rust penetration. The door opens and closes normally, and the glass has no cracks.
Emergency shutdown: If the emergency shutdown buttons on the cab and the fuselage are pressed, the engine should immediately shut down.
Fire extinguisher: If equipped, the pressure is normal and it is within the valid period.
Reverse camera/radar (if equipped): The rearview camera provides clear images, and the reverse radar function works effectively. The dump truck is large in size, and there is a large blind spot when reversing.
11. Dynamic performance testing
Carried out in a safe area or on a dedicated test track:
Driving performance: The gear shifting between forward and reverse gears is smooth without any abnormal shocks. When driving in a straight line, there is no snake-like movement (snake-like movement indicates excessive articulation gap). The engines of the dual-engine model are synchronized well at both the front and rear.
Hinged steering: Full-angle steering in both directions, with smooth operation without any jamming or abnormal noises. The steering limit position is reliable.
Bucket movement:
The lifting of the bucket is smooth throughout the entire range, and the lifting speed meets the standards.
The opening and closing actions of the bucket are smooth and continuous. After closing, it fits tightly against the front opening of the bucket.
The entire travel of the soil-discharging push plate is smooth, and the pushing and retraction speeds are normal. The flipping action of the tilting soil-discharging bucket is smooth.
Composite action: Simulate loading and unloading operation - Lower the bucket while moving forward, observe the coordination between the bucket movement and the vehicle's movement.
12. Deep test of the hydraulic system
Pressure test: Connect pressure gauges to the pressure measurement ports of each working circuit, and measure the overflow pressure of the bucket lifting, bucket door opening and closing, and the discharge push plate (or flipping) respectively. Compare the measured values with the manufacturer's rated values.
Pressure retention test:
Bucket lifting cylinder - Raise the bucket to its highest position, mark the position of the piston rod, turn off the engine, leave it idle for 10 minutes, and record the drop amount.
Doumen oil cylinder - Fully open the Doumen, leave it for 10 minutes, and record the amount of self-closing.
Earth removal push plate cylinder - Push the push plate to the farthest end, let it stand still for 10 minutes, and record the retraction amount.
Any sinking or displacement exceeding the manufacturer's standards indicates that there is internal leakage in the cylinder or leakage in the directional control valve.
13. Special test for earth excavation and loading/unloading (optional, strongly recommended)
On the prepared earthwork operation area, conduct a full-process test covering short-distance loading, transportation and unloading of soil:
Loading and unloading performance: Lower the bucket and open the bucket door. Move forward at the working gear for loading. Observe whether the bucket is smoothly inserted into the soil, whether the full bucket rate is met, and whether the engine shows severe speed drop or black smoke emission.
Transportation status: Raise the bucket and close the bucket door. Drive at high speed for a short distance. Observe whether the bucket is stable and check for any soil leakage.
Excavation and spreading: Open the bucket door, operate the dumping push plate (or flip the bucket), and check if the soil is completely excavated and if the spreading thickness is uniform and controllable.
Thermal balance: Immediately after the test, use an infrared thermometer to measure the temperatures of the hydraulic oil tank, hydraulic pump, and gearbox housing. There should be no abnormal overheating. Recheck for any new leaks at each hydraulic joint and oil cylinder.
14. Oil sample collection and analysis (strongly recommended)
Extract samples of engine oil (from both the front and rear engines), transmission oil, hydraulic oil, and drive axle gear oil, and send them to the laboratory for elemental spectroscopy analysis.
Abnormal iron and copper elements in the transmission oil indicate that the gears or bearings are worn out.
An increase in silicon content in the hydraulic oil indicates that external dust has infiltrated (due to poor sealing).
An abnormal increase in iron content in the drive axle gear oil indicates that the differential or the wheel hub reducer is abnormally worn.
15. Report Output
Summarize all inspection items, measurement data (such as bucket edge thickness, hinge gap, pressure retention settlement amount, oil analysis results, etc.), dynamic tests and bucket loading test records. Mark the qualified items, observation items, general defects and serious defects. Form a "Third-party Loader Inspection Report" that includes photos with PIN codes, photos of bucket edge thickness measurement, photos of hinge gap measurement, and photos of hydraulic pressure retention test. Deliver this report to the client.
III. Important Notes
Bucket assembly - The core of the overall machine's value and efficiency
The wear of the bucket edge and the bottom plate directly affects the loading efficiency and service life. Excessive wear of the edge will lead to a significant increase in cutting resistance, a sharp rise in fuel consumption, and a decrease in the full bucket rate. During inspection, an ultrasonic thickness gauge must be used for grid-point measurement, and the thinnest point thickness should be recorded. This is the key data for valuation and determining whether a major repair is necessary.
The poorly sealed hopper causes soil leakage during transportation, which not only reduces efficiency but also the spilled soil chunks may injure the following vehicles or pedestrians when traveling at high speed. The gap between the hopper and the front opening of the bucket must be measured with a feeler gauge. If it exceeds the standard, it needs to be adjusted or the sealing strip replaced.
If the gap between the earth-discharging push plate and the inner wall of the bucket is too large, it will result in incomplete earth removal, an increase in the amount of soil remaining in the bucket, and a decrease in the effective capacity. The accumulated soil in the bucket over time will harden, further exacerbating the wear.
Hinged system - Dual guarantee for driving safety and operation accuracy
The load borne by the articulation point of the loader is much greater than that of the loader or the scraper, because the bucket is located between the front and rear axles. During bucket loading, the articulation point bears a huge bending moment. Excessive articulation clearance will cause the vehicle to veer during driving, inaccurate positioning of the bucket, and in extreme cases, the articulation pin shaft to break. The clearance must be quantitatively measured using a dial indicator and cannot be determined by feel.
The pressure retention function of the articulated steering cylinder fails, which will cause the angle of the front and rear frames to be out of control during driving, resulting in extremely dangerous consequences. During inspection, it is necessary to test the pressure retention capability of the steering cylinder after it is locked at any angle.
Hydraulic system - one of the systems with the greatest load
The hydraulic system of the loader reaches its peak pressure during the loading operation and this pressure lasts for a long time. The oil temperature is prone to rise sharply. The hydraulic oil oxidizes rapidly at high temperatures, resulting in a decrease in viscosity and increased leakage and poor lubrication. During inspection, the color and odor of the hydraulic oil must be checked. If conditions permit, samples should be taken for testing the cleanliness and viscosity.
The hydraulic hoses in the bucket area are exposed to the harsh conditions of soil, stones and frequent bending. External rubber wear and aging are common failures.
The degree of wear on the outer rubber must be checked for each individual part. The exposed steel wire layer indicates that the part must be replaced immediately.
Synchronization control of dual-engine models
The front and rear engines of the dual-engine excavator must work synchronously; otherwise, it will cause the gearbox to slip, abnormal wear of the tires, and even damage to the transmission system. During the dynamic test, it is necessary to verify the synchronization of the front and rear engines during acceleration and deceleration, and the engine speeds displayed on the instrument should be basically the same.
Safety - The huge bucket and moving parts are the death zone.
During the inspection period, no one is allowed to enter the area below the bucket when it is raised. When the earth-discharging push plate or the bucket is being moved, the rear and side areas are all dangerous zones.
When the loader is unloading soil and spreading it, there is a large range of movement space at the rear. The inspector must stand in a position within the operator's line of sight and ensure it is safe.
The dual-engine excavator has two engine compartments at the front and rear. During inspection, be cautious of the high-temperature exhaust pipes and rotating fans as they pose potential hazards.
Key points for photo archives
The PIN code and the entire machine's nameplate are independently archived. The ultrasonic thickness gauge reading of the bucket edge is displayed in the same frame as the measurement position. A close-up of the measurement process of the hinge pin shaft dial indicator. Photos of the gap measurement between the bucket door and the front opening of the bucket using a feeler gauge. Photos of the gap measurement between the dumping push plate and the inner wall of the bucket. Photos of the start and end marks of the hydraulic pressure holding test. Panoramic photos of the full bucket state during the bucket loading test. Photos of the label of the oil sample bottle corresponding to the sampling point.
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Inspection methods, procedures and precautions for excavators
The excavator is an indispensable and highly efficient earth-moving machinery in large-scale infrastructure construction, open-pit mining spoil removal, and agricultural water conservancy renovation projects.