Diagnosis method of hydraulic system failure of construction machinery

1. Visual inspection method

For some relatively simple faults, parts can be inspected by means of visual inspection, hand mold, ear listening and smelling.

For example, faults such as cracks, oil leakage, looseness and deformation can be found through visual inspection, so that parts can be repaired or replaced in time; There will be a vibrating feeling when the pressure oil flows, but there is no such phenomenon when there is no oil flowing or the pressure is too low. In addition, hand touch can also be used to judge whether the lubrication of hydraulic components with mechanical transmission parts is good. Feel the temperature change of the component shell with your hand. If the component shell is overheated, it means that the lubrication is poor; you can judge the mechanical parts by hearing. The fault point and degree of damage caused by the damage, such as hydraulic pump suction, overflow valve opening, component card issuance and other faults will produce abnormal sounds such as water impact sound or 'water hammer'; some parts may be caused by overheating, poor lubrication and cavitation. If there is a peculiar smell due to other reasons, the fault point can be judged by smelling it.

2. Replacement diagnostic method

This method should be used when there is a lack of diagnostic instruments at the maintenance site or when the inspected components are too precise to be disassembled. First, remove the components suspected to be faulty and replace them with new ones or components of the same type that work normally on other machines and test to see if the fault can be eliminated to make a diagnosis. For example, the working pressure of the hydraulic system of the working device of a Cat E200B excavator was suspected to be the failure of the main safety valve according to experience. Works fine, confirming the suspicion is correct. Using the swap diagnosis method to check the fault, although it may be troublesome to operate due to factors such as structure, on-site component storage or inconvenient disassembly, etc., for small and easy-to-use components such as balance valves, relief valves, and one-way valves. It is more convenient to use this method for disassembled components. The swap diagnosis method can avoid the performance degradation of hydraulic components caused by blind disassembly. For the above faults, if there is no need to check the replacement method, but directly remove the suspected main safety valve and disassemble it, if there is no problem with the component, its performance may be affected after reassembly.

3. Instrument measurement and inspection method

Instrument measurement and inspection method is to judge the fault point of the system by measuring the pressure, flow and oil temperature of the hydraulic oil in each part of the hydraulic system. In general on-site testing, the failure of the hydraulic system is often manifested as insufficient pressure, which is easy to detect; while the detection of flow is more difficult, and the size of the flow can only be roughly judged by the speed of the action of the actuator. Therefore, in the field inspection, more methods are used to detect the system pressure.