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? Loss of lubricating oil in the moving parts: Whether it is a lubricated compressor or an oil-free compressor, its moving parts (crankshaft, connecting rods, crosshead components) require lubricating oil to ensure better mechanical efficiency and to reduce energy consumption and temperature increases caused by friction. Various types of compressors, especially those that use air as the compression medium, often encounter the following situation: a compressor that appears to be operating normally still requires its lubricating oil in the oil reservoir to be replenished after just a few days, indicating significant oil loss. When checking for any oil leakage defects in the engine block, it was found to be in excellent condition, with no signs of lubricant leakage. So how did such a large amount of lubricating oil disappear so mysteriously? We conduct a detailed analysis of this issue to avoid the serious consequences that may result from loss of lubrication. The poor performance of the wiper components leads to the loss of lubricating oil. Improper structural design of these components, incorrect installation, poor quality of the manufactured parts, as well as wear resulting from prolonged operation of the wiper rings, can all result in a diminished ability of the wiper components to remove oil. This allows the lubricating oil in the engine’s oil sump to flow into the collection container through the gap between the piston rod and the wiper rings. In compressors without a suction tube structure, the lubricating oil enters the cylinder directly through the packing seal ring and throttle ring, resulting in loss of lubricating oil. If the amount of lubricating oil entering the sump or cylinder is excessive, there is definitely a problem with the wiper. This can be resolved using the following methods: a. Disassemble the wiper components to check whether the direction of the wiper rings is incorrect, which may prevent them from performing their function of removing oil effectively. The correct installation direction is such that the blade of the one-way oil-scraping ring faces the fuselage side. b. Check the wear condition of the oil-scraping ring, and verify whether the tension spring is still capable of holding the ring in place. If the oil scrapper ring is severely worn, it should be replaced with a new one; if the tension spring has failed, it must also be replaced. It is recommended to turn a rod made of carbon steel or cast iron using a lathe, then grind it to the same diameter as the piston rod. The oil scrapper ring should be installed on this rod (with the spring used to secure it in place). A small amount of lubricant can be applied to the friction rod, allowing the oil-scraping ring to move back and forth along the rod. The purpose of this is to remove any burrs on the oil-scraping ring, thereby enabling its cutting edge to fit closely against the piston rod and improving its ability to scrape off oil. c. Check the gap between the wiper ring and the wiper box; if the gap is too small or non-existent, it can prevent the wiper ring from moving freely inside the wiper box, preventing its cutting edge from making close contact with the piston rod, and thus rendering the wiper ring ineffective at removing oil. Conversely, if the gap is too large, due to the back-and-forth movement of the piston rod, the oil-scraping ring will move along with it and continuously strike the oil-scraping box from side to side; as a result, the oil-scraping ring is also unable to perform its function of scraping oil effectively. The correct installation clearance between the oil wiper ring and the oil wiper box should be between 0.05–0.1 mm. d. Structural design of the oil scraper component: The oil scraper component serves as a barrier to prevent the leakage of lubricating oil inside the aircraft body, and a rational design of its structure is crucial. As the crankshaft rotates, it strikes the lubricating oil in the engine’s oil sump, causing the oil to splash. Similarly, as the crosshead moves back and forth along its sliding track, it also impacts the lubricating oil, leading to splashing of the oil. If the oil baffle of the wiper component cannot cover the majority of the splashing lubricating oil, then even the best-performing wiper rings will not be able to remove such a large amount of lubricating oil. Therefore, the structural design of the wiper component is very important; it is necessary to ensure that its structure can prevent the majority of the splashing lubricating oil from entering the interior of the wiper component, thereby reducing the workload on the wiper ring. At the same time, the oil return port of the oil-scraping box must be designed in such a way that all the lubricating oil scraped off by the oil-scraping ring flows back into the aircraft’s oil tank. Seal leakage is also a key factor in lubricant loss. Many people assume that lubricant loss and seal leakage are two unrelated issues, but this is not the case. Based on years of work experience and on-site inspections, the author concludes that filler leakage is the most important and direct cause of lubricant loss in air compressors. Taking the 5L-40% and 4L-20% air compressors, which are designed according to national unified standards, as examples, these two types are the most commonly used models in air compressor stations. The packing components of these compressors feature a combined structure in which the oil-scraping ring is located at the bottom (near the body of the compressor), while the packing seal ring is located at the top (on the side of the cylinder). Such a packing component serves both to scrape off oil and prevent lubricating oil in the engine body from entering the cylinders, as well as to seal the gases inside the cylinders and prevent them from escaping. When the wiper is not functioning properly and cannot remove all the lubricating oil adhering to the piston rod, the lubricating oil will enter the cylinder through the gap between the piston rod and the wiper ring, resulting in loss of lubricating oil. If the sealing ring of the filler does not function properly, a negative pressure is created in the first cylinder as the piston component moves toward the cylinder head (i.e., during the headstroke). This fact can be clearly demonstrated through thermodynamic calculations carried out during the design of piston compressors. A large amount of oil and gas inside the engine block is drawn into the cylinders, especially when the oil scrapper rings do not function properly; at such times, oil mist and liquid lubricant end up in the cylinders. Imagine, with the piston of the compressor moving back and forth hundreds of times per minute, how much oil-containing gas (and in severe cases, liquid lubricant) will be drawn into the cylinder? The rate at which its lubricating oil is lost is extremely high; this is why, even in the absence of any defects in the compressor’s structure that could cause leaks, large amounts of lubricating oil still get lost. The simplest and most straightforward way to determine whether excessive loss of lubricant is caused by a faulty wiper ring or an imperfect packing seal is to open the drain valve of the intercooler, and to check for any leakage of lubricant by observing the color of the liquid that comes out of the valve. When the liquid discharged is milky white (a mixture of lubricant and water forms a milky-white solution, similar to soapy water), it indicates that a large amount of lubricant has entered the cylinder. At this point, the packing components must be inspected, and new packing seals, throttle rings, and oil-scraping rings need to be replaced. Incidentally, I would like to mention that workers operating compressors should pay attention to draining the oil-water mixture accumulated in the intercooler of the air compressor in a timely manner, in order to prevent liquid slugging incidents that could lead to damage to the compressor equipment. Especially on rainy days in summer, due to high air humidity and significant condensation, it is necessary to open the drain valve multiple times per shift to drain the liquid. When the discharge is clean water, it indicates that the compressor packing components (oil scrapper ring and seal ring) are functioning properly. In oil-lubricated compressors where the cylinders are lubricated with oil, it is also normal for the oil-water mixture discharged from the drain valve to have a very light milky white color. If the liquid discharged from the drain valve is milky white, it indicates that a significant amount of lubricating oil has entered the cylinder; in such cases, the wiper ring and seal ring should be replaced promptly. Otherwise, not only will a large amount of valuable lubricant be wasted, but the loss of lubricant can also lead to serious consequences. The impact of respirators on lubricant consumption: The piston compressor’s frame contains components such as the crankshaft, connecting rods, and crosshead mechanisms, which constitute the heart of the compressor. The lower part of the frame stores lubricant as well as the lubricant that leaks from these mechanisms, serving as a tank – essentially a sealed container. For ventilation inside the machine body, and to prevent the vaporization of lubricating oil from creating high concentrations of flammable gases that could lead to combustion and explosion, strict process requirements mean that compressors typically use nitrogen displacement. Most compressors achieve this by installing one or several breathers on the casing. Another important function of the respirator is to mitigate the negative pressure suction caused by leaks in the packing components, thereby maintaining the balance of the lubricating oil. Therefore, ensuring that the components of the respirator are in proper working condition is crucial for preventing the consumption of lubricating oil, and this matter should be given high priority. The components of the respirator should be checked regularly for blockages. If the metal mesh of the respirator is clogged with oil, it should be removed, cleaned thoroughly with a cleaning agent such as carbon tetrachloride, dried, and then reinstalled in place.