The failure of the hydraulic system of the loader working device is a common failure during the use of the loader. How to determine the fault accurately can enable the repair work to be targeted and achieve the best repair effect. First, the failure of the failure loader work unit hydraulic system failure, not sudden, generally have some signs of the phenomenon, such as vibration, noise, temperature rise, intake, pollution, leakage and so on. If you can find it as soon as possible and take appropriate measures, the fault will be avoided or reduced. Second, the fault parameters The main parameters of the hydraulic system fault pressure, flow, temperature, the movement speed of the actuator, noise, vibration, oil viscosity, oil pollution and leakage. When measuring different parameters, different test methods and tools and instruments can be selected according to the fault conditions of the hydraulic system and different technical accuracy requirements. Such as: pressure gauges, flow meters, thermometers, oil condition detectors. Third, the diagnosis and detection methods 1. "Four" diagnosis. Technicians use tactile, visual, auditory and olfactory senses to determine the failure of the hydraulic system. This is an easy way to obtain fault information in the field. Even the most advanced diagnostic device must be combined with the “four-leakage†diagnostics. Through the "four-legged" diagnosis, the vibration, fluid temperature, actuator operating conditions, abnormal sound, fluid status, and external leaks can be used to determine the fault. 2. Sequence inference. This diagnostic method requires the host to stop working. According to the “four-leap†judgment method, it initially determines the scope of the fault, so as to reduce the fault to the minimum range, then analyze the reasoning sequentially and gradually approach the fault location. 3. Take fault test instrument diagnosis. (1) Detection of hydraulic pump. As shown in Figure 1, the access tester, the hydraulic pump and the system are isolated and not protected and controlled by the relief valve. Turn on the tester's control valve and start the engine to run at rated speed. Observe and note the flow reading at no load, then slowly close the tester's control valve so that the pressure on the tester rises gradually to the system's rated pressure. If the reading on the flowmeter is equal to the rated flow at this time, it proves that the hydraulic pump is in good condition; if the reading on the flowmeter is reduced by 25%, it means that the hydraulic pump is faulty; if the flow is reduced by 35%, it can be concluded that the failure of the hydraulic system is Caused by the oil pump. If the pointer of the pressure gauge jumps, there is a leak in the oil suction of the hydraulic pump. (2) Inspection of relief valve. Connect the tester to the hydraulic circuit shown in Figure 2. First place the tester's control valve in the idle position, then start the engine running at the rated speed, slowly rotate the tester's control valve, the pressure gauge reading should be the hydraulic system relief valve setting value, if not reach Standard value, adjustable overflow relief valve pressure. When the oil pump is in good condition, the data displayed by the tester should be equal to the set flow of the hydraulic pump before the relief valve is completely opened. Otherwise, it indicates that the overflow valve is leaking. (3) Directional control valve detection. As shown in Figure 3, access the tester, open the control valve of the tester, start the engine, run at rated speed, the oil passing through the directional control valve must pass the tester to return to the tank. Write down the flow reading in no-load condition. Then slowly load, stop loading before the pressure is lower than the system pressure (rated), observe the flow value, if the flow value and the no-load flow are basically the same, indicating that the direction of the control valve is good, if the flow loss Large, indicating that the valve should be overhauled or replaced. The above is the fault diagnosis method of the hydraulic system of the loader working device. The improvement of the ability to solve practical problems on site requires the efforts of both theory and practice to gradually accumulate experience. Author: China Railway Tunnel Group Co., Ltd.