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Maintenance and repair of small excavators

1. The engine speed of the small excavator decreases  First, the output power of the engine should be tested. If the output power of the engine is lower than the rated power, the cause of the failure may be poor fuel quality, low fuel pressure, incorrect valve clearance, and a certain cylinder of the engine does not work , The fuel injection timing is wrong, the fuel quantity is set incorrectly, the air intake system is leaking, the brake and its control lever are faulty, and the turbocharger is carbonized. If the output power of the engine is normal, it is necessary to check whether the flow rate of the hydraulic pump does not match the output power of the engine. The speed of the small hydraulic excavator is inversely proportional to the load during operation, that is, the product of the flow rate and the output pressure of the pump is an invariant, and the output power of the pump is constant or approximately constant. If the pump control system fails, it will not be able to achieve the optimal load matching state of the engine, pump and valve in different working conditions, and the small excavator will not work normally. Such failures should start with the electrical system, then check the hydraulic system, and finally check the mechanical transmission system.

2. The working speed of the small excavator slows down. The main reason for the slower working speed of the small excavator is the decrease of engine power and the internal leakage of the hydraulic system caused by the wear of various parts of the whole machine. The hydraulic pump of a small excavator is a variable displacement plunger pump. After a certain period of operation, the internal hydraulic components (cylinder block, plunger, valve plate, nine-hole plate, turtle back, etc.) inevitably produce excessive wear and tear, which will cause internal leakage. , The parameter data is not coordinated, resulting in insufficient flow and high oil temperature and slow working speed. At this time, the whole machine needs to be overhauled, and the parts that wear out of the limit are repaired and replaced. But if it is not for a small excavator with a long working hours to suddenly slow down, you need to check the following aspects. First check whether the circuit fuse is open or short, then check whether the pilot pressure is normal, then check whether the servo control valve-servo piston is stuck and whether the distributor confluence is faulty, etc., and finally the hydraulic pump is disassembled for data measurement to confirm the problem of the excavator .

3. Weakness of small excavators   Weak digging is one of the typical failures of small excavators. There are two conditions for digging weakness: one is digging weakness, the engine does not hold the car, and the load is very light; the second is digging weakness, when the boom or stick is extended to the end, the engine is severely suffocated or even stalled .

①The excavation is weak but the engine does not hold back the car. The size of the digging force is determined by the output pressure of the main pump, and whether the engine is holding back depends on the relationship between the absorption torque of the oil pump and the output torque of the engine. The engine does not hold back the car, which means that the oil pump has a small absorption torque and the engine load is light. If there is no obvious abnormality in the working speed of the small excavator, you should focus on checking the maximum output pressure of the main pump, that is, the system overflow pressure. If the measured value of the overflow pressure is lower than the specified value, it indicates that the set value of the overload relief valve of the hydraulic circuit of the mechanism is incorrect, which causes the mechanism to overflow prematurely and work weakly. You can adjust the machine by turning the adjustment screw.

②The excavation is weak and the engine is holding back the car. The engine holding the car indicates that the absorption torque of the oil pump is greater than the output torque of the engine, which causes the engine to be overloaded. For such failures, first check whether the engine speed sensing system is normal. The inspection method is similar to the engine inspection method described above. After the above meticulous inspection and troubleshooting, the engine speed sensing system returns to its normal function, the engine holding back phenomenon disappears, and the digging force will return to normal.

4. Common faults in the excavation process of small excavators Some common faults often occur in construction operations of small excavators, such as: the excavator runs off track, the reason may be the damage of the walking distribution oil seal (also known as the center rotary joint oil seal) ; The flow rates of the two hydraulic pumps are different; there is a problem with the motor while walking. If the hydraulic cylinder drains quickly, it may be because the safety relief valve is not tightly closed, or the cylinder oil seal is severely damaged, etc.

5. Daily maintenance of small excavators In order to prevent the failure of small excavators, it is necessary to pay great attention to the maintenance of small excavators during daily use. Daily maintenance includes checking, cleaning or replacing the air filter element; cleaning the inside of the cooling system; checking and tightening the track shoe bolts; checking and adjusting the track back tension; checking the air inlet heater; replacing the bucket teeth; adjusting the bucket gap; checking the front window Clean the liquid level; check and adjust the air conditioner; clean the floor in the cab; replace the filter element of the breaker (optional). When cleaning the inside of the cooling system, after the engine is sufficiently cooled, slowly loosen the water injection cap to release the internal pressure of the water tank, and then discharge the water; do not clean when the engine is working, the high-speed rotating fan will cause danger; when cleaning or replacing the cooling When liquid, the machine should be parked on a level ground.

At the same time, you need to check the height of the coolant level (add water) before starting the engine; check the engine oil level, add oil; check the fuel level (add fuel); check the hydraulic oil level (add hydraulic oil); check the air filter element Check whether it is blocked; check the wire; check whether the horn is normal; check the lubrication of the bucket; check the water and sediment in the oil-water separator.

 

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