1. Ask
"Ask" is to ask the operator about the basic situation of the faulty machine. It is mainly to understand what abnormal phenomena exist in the machine and whether the faults are sudden or gradual. Whether there is illegal operation and maintenance during use. Whether the hydraulic oil brand is correct and the replacement situation, the time of failure, that is, whether it occurs at the beginning of work or after a period of operation, and so on. After obtaining these information, the characteristics of the faults of the hydraulic system can be basically determined.
Generally speaking, most of the sudden failures are caused by the loose sealing of the valve caused by the dirty hydraulic oil or the broken spring. Most of the gradual failures occur due to serious wear of components or aging of rubber seals and pipe fittings.
If the excavator works normally at the beginning, but it slows down after a period of operation and is accompanied by noise and oil temperature rise (the indication of the oil temperature gauge is greater than 75 ° C), it may be caused by internal leakage of the pump or valve, except for insufficient oil, long-term heavy-duty operation in high-temperature environment, too much dirt on the radiator of the oil cooler, and fan tape slipping. For example, for an excavator, the pilot control pressure is normal at first, but soon its value drops. The inspection results showed that the rubber oil inlet pipe of the pilot pump was collapsed due to heat, which blocked the oil inlet.
2. Look
"Look" is to check the working condition of the hydraulic system through eyes. Such as whether the oil volume in the oil tank meets the requirements, whether there are bubbles and discoloration (the noise, vibration and crawling of the machine are often related to a large number of bubbles in the oil); Oil leakage at sealing parts and pipe streets; Changes in the indicated values of pressure gauge and oil temperature gauge during operation; Check whether the fault part is damaged, the connection is gradually falling off and the fixing parts are loose. In case of hydraulic oil leakage, after eliminating the insufficient or uneven torque of fastening bolts, and before replacing the oil seal that may have been seriously worn or damaged, check whether the pressure exceeds the limit. When installing the oil seal, the model and quality of the oil seal shall be inspected and assembled accurately.
3. Listen
"Listening" is to check the hydraulic system with your ears for abnormal noise. The sound of normal machine operation has a certain rhythm and rhythm, and remains stable. Therefore, be familiar with and master these laws, and maintain stability. Therefore, if we are familiar with and master these laws, we can accurately diagnose whether the hydraulic system works normally; At the same time, according to the change of rhythm and rhythm, as well as the parts where abnormal sounds are generated, the parts where the faults occur can be determined, and the parts where the faults occur and the degree of damage can be determined. For example, the high pitched screech usually means that air is sucked in; The "chirp" or "cluck" sound of the hydraulic pump is often the damage of the pump shaft or bearing; The "wheezing" sound of the reversing valve is due to insufficient opening of the valve stem; The heavy "click" sound may be the sound of overload of the overload valve. If there is cavitation sound, it may be that the oil filter is blocked by dirt, the oil suction pipe of the hydraulic pump is loose, or the oil level of the oil tank is too low.
4. Touch
"Touch" is to use sensitive finger touch to check whether the pipeline or element of the pressure system has vibration, impact, abnormal oil temperature rise and other faults. If you touch the pump casing or hydraulic parts by hand, you can judge whether there is abnormal temperature rise in the hydraulic system according to the degree of cold and heat, and identify the causes and parts of temperature rise. If the pump casing is overheated, it means that the pump has serious internal leakage or has taken in air. If the vibration is abnormal, it may be due to poor installation balance of rotating parts, loose fastening screws or gas in the system.
5. Try
"Test" is to operate the actuator of the hydraulic system of the machine and determine the fault location and cause from its working condition.
(1) All interviews. According to the design function of the hydraulic system, experiments are conducted one by one to determine whether the fault is in the local area or the whole area. If the action of the whole machine fails or is weak, first check whether the pilot control pressure is normal, whether the clutch (coupling) slips (loosens), whether the engine power is sufficient, whether the hydraulic oil volume is sufficient, and whether the hydraulic pump inlet is sealed. 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 circuit of the reversing valve, overload valve or hydraulic cylinder, independent of the hydraulic pump and the main safety valve.
(2) Exchange test. When only one circuit or one function is lost in the hydraulic system, it can be exchanged with the oil circuit with the same (or related) function to further determine the fault location. For example, the excavator has two mutually independent working circuits, and each circuit has its own components. When one circuit fails, the other pump can be connected to this circuit by exchanging high-pressure oil pipes. If the failure is still on one side, it means that the failure is not on the pump.
