1. Failure to correctly judge and analyze faults, and blind disassembly and disassembly are commonplace.
Some maintenance personnel do not clearly understand equipment structure and operating principles, fail to analyze fault causes carefully, and cannot locate the fault accurately. Relying on rough assumptions, they dismantle equipment extensively and indiscriminately. As a result, the original fault remains unresolved and poor repair skills and workmanship introduce new problems. For example, a station once experienced insufficient output from a 120 KW diesel generator, preventing the machinery from operating. Maintenance personnel dismantled the PT fuel injection pump and injectors but could not identify the cause. They replaced 1 fuel injection pump for a trial, yet the fault persisted.
The final check was that the fault was caused by excessive impurities and moisture inside the diesel fuel used. However, this disassembly resulted in a significant decline in the performance of the PT fuel injection pump and insufficient power of the diesel generator.
Therefore, when a mechanical failure occurs, it must be detected through testing equipment; if there is no testing equipment, traditional fault judgment methods and means such as "asking, looking, checking, and testing" can be used to determine the most likely fault location based on the structure and working principle of the equipment.
When determining equipment faults, the "elimination method" and "comparison method" are generally used, in the order from simple to complex, first appearance, then internal, first assembly and then components, and avoid "blind disassembly and disassembly".
2. There are many cases of not paying attention to detecting the fitting clearance of parts.
For example, in the maintenance of common diesel generator sets, various models have strict requirements on the matching clearance between the piston and the cylinder liner, the "three gaps" of the piston ring, the piston top clearance, the valve clearance, the plunger clearance, the brake shoe clearance, the main and driven gear meshing clearance, the bearing axial and radial clearance, the valve stem and the valve guide clearance, etc., and must be measured during maintenance. Parts that do not meet the clearance requirements must be adjusted or replaced.
In actual maintenance work, there are many phenomena of blindly assembling parts without measuring the fitting clearance, which leads to early wear or ablation of bearings, oil burning of diesel generators, difficulty in starting or deflagration, broken piston rings, impact of mechanical parts, oil leakage, air leakage and other faults. Sometimes, improper clearance of parts may even lead to serious damage to machinery.
3. The phenomenon of blindly replacing parts and blindly replacing parts for repairs exists to varying degrees.
It is relatively difficult to judge and eliminate equipment faults. Some maintenance personnel have always adopted the method of replacing parts for testing. Regardless of whether they are large or small, as long as the parts that are believed to be the cause of the fault are replaced one by one. As a result, not only was the fault not eliminated, but parts that should not have been replaced were replaced at will, increasing maintenance costs.
Some faulty parts can completely restore their technical performance through repair, such as generators, air compressors, blowers, burners, gear oil pumps, etc., which can be repaired without complicated repair processes. During maintenance, the cause and location of the fault should be carefully analyzed and determined based on the fault phenomenon. Repair methods should be used to restore the technical performance of the repairable parts, and blind replacement of parts should be avoided.
4. Parts may be installed backwards when assembling equipment.
Some components have strict orientation requirements during equipment maintenance, and only correct installation ensures proper operation. Certain components lack obvious external distinguishing features and can be fitted either way, so reverse installation frequently occurs in practice. This causes premature component damage, abnormal mechanical operation, and equipment damage accidents. Components particularly prone to reverse installation when their structure and installation precautions are not understood include engine cylinder head gaskets, variable-pitch valve springs, engine pistons, piston rings, fan blades, gear oil pump side plates, metal-cased oil seals, thrust washers, thrust bearings, thrust shims, oil baffle rings, fuel injection pump plungers, clutch friction-disc hubs, and propeller-shaft universal joints.
As a result, the equipment may not work properly after assembly, leading to equipment failure.
Therefore, when assembling parts, maintenance personnel must understand the structure and installation direction requirements of the parts, and cannot blindly install them for granted.
5. Maintenance methods are irregular, and "treating the symptoms but not the root cause" is still the habit of some maintenance units.
When repairing equipment, some maintenance personnel do not adopt correct maintenance methods, thinking that emergency measures are omnipotent, replacing "maintenance" with "emergency", and there are still many phenomena of "treating the symptoms but not the root cause". Such as the often encountered "welding instead of repair" is an example. Some parts can be repaired, but some maintenance personnel often use the "welding" method to save trouble; in order to make the diesel generator "powerful", the fuel supply volume of the fuel injection pump and the injection pressure of the injector are artificially increased.
These irregular maintenance methods can only be used in emergencies, but cannot be used for a long time. The cause of the fault must be found out fundamentally, and formal maintenance methods must be adopted to eliminate the fault, which should attract the attention of maintenance personnel.
(Source: Equipment Man)