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Self-diagnosis of small excavator

1. The fundamental requirements for on-site diagnosis of faults

On-site diagnosis requires the repairer to have certain common sense and practical experience of hydraulic transmission. Before making a diagnosis for a new model, carefully read the random operation and maintenance instructions to have a basic understanding of the hydraulic system of the machine.

Now, the hydraulic system of small and medium-sized excavators is almost composed of two parts: the oil circuit and the pilot operation oil circuit; the main oil circuit adopts a double pump and dual circuit variable open system, and the pilot operation oil circuit is a quantitative system. After reading the technical data, grasp the primary parameters of the system, such as the opening pressure of the main safety valve, pilot operating pressure and flow, etc.; familiarize with the schematic diagram of the system, grasp the function and relationship of each component symbol in the system, and analyze each branch circuit The function of each hydraulic component; the structure and operating principle of each hydraulic component should also be understood; the possible cause of a certain problem should be analyzed; and the location of each hydraulic component and the connection method between them should be understood with the machine. When diagnosing the problem in detail, the order of “external to internal, easy first and difficult first” should be followed, and the possible causes of a certain problem should be investigated one by one.

2. Methods to diagnose problems on site

The first method to diagnose hydraulic system faults on site is still the empirical diagnosis method. The empirical diagnosis method is a method for repairers to use the theoretical knowledge and accumulated experience that they have grasped, combined with the practice of the machine, using the means of “asking, seeing, listening, touching, and testing” to quickly diagnose the location and cause of the problem .

The details are:

1. Ask

“Ask” is to ask the operator about the basic condition of the malfunctioning machine. The first thing to understand is the abnormal phenomenon of the machine; the fault is sudden or gradual; whether there is illegal operation and repair and maintenance in use; whether the hydraulic oil trademark is correct and the status of replacement; the opportunity for the occurrence of faults is at the beginning of the operation The time is still presented after a certain period of work, and so on. After obtaining this information, you can fundamentally confirm the faulty characteristics of the hydraulic system. Generally speaking, sudden failures are mostly caused by dirty hydraulic oil or loose valve closure caused by broken springs; gradual failures are mostly caused by severe wear of components, rubber seals, and aging of pipe fittings. Introduction to excavator common sense

For example, when the excavator is normal at the beginning of the operation, but after a period of operation, the action becomes slower and accompanied by the phenomenon of noise and oil temperature rise (the indicator of the oil temperature gauge is greater than 75°C), it is necessary to remove the lack of oil and high temperature environment. Not long-term heavy-duty work, too much dirt on the radiator fins of the oil cooler, and slippage of the electric fan tape may be caused by internal leakage in the pump or valve. For example, for an excavator, the pilot operating pressure is normal at first, and its value does not drop shortly afterwards. The result is that the rubber oil inlet pipe of the pilot pump was heated and collapsed, which caused the oil inlet to be blocked.

2. Look

“Seeing” is to check the working condition of the hydraulic system through the eyes. For example, whether the amount of oil in the fuel tank meets the requirements, whether there are bubbles and discoloration (the noise, vibration, and crawling of the machine are often related to many bubbles in the oil); the oil leakage in the sealing parts and pipe streets; pressure gauges and The indicator value of the oil temperature gauge changes during operation; whether the faulty part is damaged, the connection gradually falls off, and the fixing parts are loose. When there is a problem with hydraulic oil leakage, after removing the lack or uneven torque of the forbidden bolt, before replacing the oil seal that may have been severely worn or damaged, you should also check whether the pressure exceeds the limit. When installing the oil seal, check the type and quality of the oil seal, and perform accurate assembly. Excavator common sense compilation

3. Listen

“Listening” is to check with your ears for abnormal noises in the hydraulic system. Normal machine operation has a certain rhythm and rhythm, and maintains stability. Therefore, be familiar with and grasp these rules and maintain stability. Therefore, if you are familiar with and grasp these rules, you can accurately diagnose whether the hydraulic system is working properly. At the same time, according to the changes in rhythm and rhythm, and the parts where abnormal sounds occur, you can confirm the parts that have occurred, and then you can confirm the failure. The location of the attack and the extent of the damage. Such as the high-pitched whistling sound, usually sucked in air; the “chittering” or “chuckling” sound of the hydraulic pump is often caused by damage to the pump shaft or bearing; the reversing valve announces the “chipping” sound, which is the opening of the valve stem. Lack of degree; rough “click” sound, perhaps the sound of overload valve overload. If it is cavitation, it may be that the oil filter is blocked by dirt, the suction pipe of the hydraulic pump is loose, or the oil level of the oil tank is too low by one level.

4. Touch

“Touching” is to use sensitive finger touch to check whether the pipelines or components of the pressure system have oscillations, shocks, and abnormal oil temperature rise. If you touch the pump casing or hydraulic parts with your hands, you can judge whether the hydraulic system has abnormal temperature rise based on the degree of heat and cold, and identify the cause and location of the temperature rise. If the pump casing is overheated, it means that the pump has severe leakage or air has been sucked in. If you feel that the oscillation is abnormal, it may be due to poor balance of the reversal component device, loose tightening screws, or gas in the system.

5. Try

“Testing” is to operate the performance components of the machine’s hydraulic system to determine the location and cause of the fault from its operating conditions. Questions and answers about excavators

(1) Comprehensive test. According to the design function of the hydraulic system, experiment one by one to confirm whether the fault is in part of the area or in the whole area. If the whole machine fails or is weak, you should 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 volume is sufficient, and the sealing condition of the hydraulic pump inlet. If the symptoms of an excavator are only manifested as the active boom of the boom, the cause of the problem may be in the oil circuit of the reversing valve, overload valve or hydraulic cylinder, and has nothing to do with the hydraulic pump and the main safety valve.

(2) Exchange test. When only a certain circuit or a certain function is lost in the hydraulic system, it can communicate with the oil circuit of the same (or related) function to further confirm the faulty part. For example, the excavator has two independent operating circuits, each of which has its own components. When a circuit breaks down, the other pump can be connected to this circuit through the AC high-pressure tubing. If the failure is still on one side , It clarifies that the problem is not on the pump.

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