First, the basic requirements for on-site diagnosis of faults
On-site diagnosis requires maintenance personnel to have certain knowledge and practical experience in hydraulic transmission. Before troubleshooting a new model, carefully read the random use and maintenance instructions to have a basic understanding of the hydraulic system of the machine. At present, the hydraulic system of small and medium-sized excavators is almost composed of two parts: the oil-filling road and the pilot-operated oil circuit; the main oil circuit adopts the double-pump dual-circuit variable open system, and the pilot control oil circuit is a quantitative system. By reading the technical data, master the main parameters of the system, such as the opening pressure of the main safety valve, the pilot operating pressure and flow rate; familiar with the schematic diagram of the system, master the functions and relationships of the various components in the system, analyze each branch circuit The function; the structure and working principle of each hydraulic component should also be understood; analyze the possible causes of a fault; check the location of each hydraulic component and the connection between them. When diagnosing a fault specifically, you should follow the order of “external to internal, first easy and then difficult†to check the possible causes of a certain fault one by one.
Second, the method of on-site diagnosis of faults
The main method for on-site diagnosis of hydraulic system failures is empirical diagnostics. The empirical diagnosis method is that the maintenance personnel use the theoretical knowledge and accumulated experience, combined with the actual situation of the machine, and use the means of “question, see, listen, touch, test†to quickly diagnose the fault location and cause. method. Specifically:
1, ask
“Q†is to ask the operator about the basic situation of the faulty machine. Mainly understand the abnormal phenomena of the machine; whether the fault is sudden or gradual; whether there is violation operation, maintenance and repair; whether the hydraulic oil grade is correct and replaced; the timing of the fault occurs at the beginning of the work It still appears after a period of work, and so on. Once this information is available, the characteristics of the fault in the hydraulic system can be determined. In general, sudden failures are mostly caused by poorly closed valves due to excessive hydraulic oil or spring breaks; most of the failures occur due to severe component wear or rubber seals and tube aging.
If the excavator starts to work normally, but after the working period becomes slow, and the noise and oil temperature rise (the oil temperature meter indicates more than 75 °C), the non-oil shortage and high temperature environment are excluded. In the case of heavy load operation for a long time, too much dirt on the radiator fins, and slippage of the fan tape, it may be caused by a leak in the pump or valve. For example, an excavator initially had normal pilot pressure and its value did not drop soon. The result of the inspection is that the rubber inlet pipe of the pilot pump is heated and folded, causing the oil to be blocked.
2, look
“Looking†is to see how the hydraulic system works through the eyes. If the amount of oil in the fuel tank meets the requirements, whether there are bubbles or discoloration (the noise, vibration and creep of the machine are often related to a large number of bubbles in the oil); oil leakage at the sealing part and the street of the pipe; pressure gauge and The oil temperature gauge indicates the change of the value during the work; the fault location has no damage, the connection gradually falls off and the fixing member loosens. When there is a fault in the leakage of hydraulic oil, after eliminating the insufficient or uneven torque of the forbidden bolt, check whether the pressure is over-limit before replacing the oil seal that may have been seriously worn or damaged. When installing the oil seal, the type and quality of the oil seal should be checked and assembled accurately.
3, listen
“Listen†is to check the hydraulic system for abnormal noise with your ear. Normal machine operation sounds have a certain rhythm and rhythm, and remain stable. Therefore, familiarize yourself with and master these laws and remain stable. Therefore, by familiarizing with and mastering these laws, it is possible to accurately diagnose whether the hydraulic system is working properly. At the same time, according to the changes in the rhythm and temperament, and the components generated by the abnormal sound, the fault occurrence component can be determined, and the fault can be determined. The location and extent of damage. For example, the whistling sound of a high-pitched sound is usually sucked into the air; the "喳喳" or "giggle" sound of the hydraulic pump is often damaged by the pump shaft or the bearing; the reversing valve makes a "beep" sound, which is the valve stem open. Insufficient degree; the thick "beep" sound may be the sound of the overload valve overload. If it is cavitation, it may be that the oil filter is clogged with dirt, the hydraulic pump suction pipe is loose, or the oil level of the oil tank is too low.
4, touch
“Touch†is the use of sensitive finger touch to check whether the piping or components of the pressure system are vibrating, impacting, and abnormal oil temperature rise. If you touch the pump casing or hydraulic parts by hand, you can judge whether the hydraulic system has abnormal temperature rise according to the degree of heat and cold, and determine the cause and location of the temperature rise. If the pump casing is overheated, the pump is leaking heavily or sucking in air. If the vibration is abnormal, it may be that the rotating parts are not well balanced, the fastening screws are loose, or there is gas in the system.
5, try
"Try" is to operate the actuator of the hydraulic system of the machine, and determine the location and cause of the fault from its working condition.
(1) Comprehensive test. Experiments are performed one by one based on the design capabilities of the hydraulic system to determine if the fault is in a local area or in a full area. If the whole machine fails or is weak, first check whether the pilot operating pressure is normal, whether the clutch (coupling) is slipping (loose), whether the engine power is sufficient, whether the hydraulic oil is sufficient and the sealing of the hydraulic pump inlet. If the fault symptom of an excavator is only the automatic lowering of the boom, the cause of the fault may be in the oil passage of the reversing valve, the overload valve or the hydraulic cylinder, and is independent of the hydraulic pump and the main safety valve.
(2) Exchange test. When only one loop or a certain function is lost in the hydraulic system, it can be exchanged with the same (or related) function of the oil circuit to further determine the fault location. If the excavator has two independent working circuits, each circuit has its own components. When one circuit fails, the other pump can be connected to the circuit by exchanging the high pressure oil pipe. If the fault is still on one side. , indicating that the fault is not on the pump, the other components of the loop should be checked; otherwise, the fault is on the pump. Another example is the running device of an excavator. When there is a fault that one side can walk and the other side cannot walk or automatically deflect, the two newly purchased motor tubes can be reversed to determine whether the faulty part is on the motor or in the reversing valve. .
(3) Replacement test. Replace the suspected component with a component that is in good technical condition and verify that the component is faulty by comparing the phenomenon reflected before and after the component is replaced.
(4) Adjustment test. Adjust the relief valve or the reversing valve of the system and compare the changes of the working conditions before and after the adjustment to diagnose the fault. When the pressure of the hydraulic system is adjusted, if the pressure (pressure gauge indication table) does not reach the specified value or rises and then drops, it indicates that the leakage inside the system is serious.
(5) Open circuit test. Remove one of the system's tubing (or loosen the fitting) and observe the oil condition to check which section of the oil circuit the fault occurred.
Finally, it is recommended that the maintenance personnel make a record of the fault diagnosis, collect the phenomena, causes and elimination methods of the failure, and continuously accumulate and improve in the actual work.
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