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Common faults and solutions of reciprocating piston air compressors. Reciprocating piston air compressors play an extremely important role in the flexible packaging plastics industry. For example: it is used on a punching machine for pneumatic punching during bag manufacturing ； When printing plastics, it is also used on cylinders to lift and lower the offset printing rollers. Reciprocating piston compressors offer excellent performance, featuring low noise, low fuel consumption, and low specific power. However, in operation they are prone to problems such as reduced displacement, high exhaust temperature, high oil temperature, knocking noises, and piston jamming or seizure. Reciprocating piston air compressors play an extremely important role in the flexible packaging plastics industry. For example: it is used on a punching machine for pneumatic punching during bag manufacturing ； When printing plastics, it is also used on cylinders to lift and lower the offset printing rollers. Reciprocating piston compressors offer excellent performance, featuring low noise, low fuel consumption, and low specific power. However, in operation they are prone to problems such as reduced displacement, high exhaust temperature, high oil temperature, knocking noises, and piston jamming or seizure. I. Working principle of reciprocating piston air compressors: A reciprocating piston air compressor is typically driven by an electric motor, which rotates a shaft through a V-belt; the piston then moves back and forth via connecting rods, causing changes in the volume of the piston chamber formed by the air valves, piston, and cylinder, thereby achieving the compression of air. Compressed air is compressed again through an intercooler, and finally enters the air storage tank. The air storage tank is mainly composed of a cylinder, pressure gauge, safety valve, etc., and it can stabilize the pressure in the air pipeline, reducing the pressure fluctuations caused by the operation of the compressor. If, for some reason, the compressed air inside exceeds the rated pressure, the safety valve will open automatically to release the compressed air into the atmosphere, ensuring safe operation. Our factory uses V-0.3/10 and W-0.6/10 type air compressors produced by Fujian Compressor General Factory, with the opening pressure of the safety valves being 1.05 to 1.08 times the rated exhaust pressure. Of course, the opening pressure of the safety valve varies for air compressors of different specifications. II. Pre-production inspection Before starting the air compressor, it is necessary to conduct some inspections to rule out potential faults. Pre-start checks mainly include checking the power supply voltage and the oil level. Power supply voltage: The allowable fluctuation range for the power supply voltage is around ±5%. Oil level check: The oil level should generally be between 1/3 and 2/3 of the oil gauge. When the oil level is 1/3 below the mark, filtered lubricant of the same grade should be added promptly; 13# compressor oil is suitable for winter use, while 19# compressor oil is appropriate for summer use. Use SAE30 when the temperature is above 10°C, and SAE10 when it is below 10°C. III. Decreased displacement 1. Lack of oil – A decrease in displacement is directly related to a lack of oil. Once during production, the air compressor developed a problem of reduced exhaust volume; it was unable to raise or lower the pressure rollers of the printing machine, and there was also a certain knocking sound coming from the cylinder. We first inspected the air silencer and cleaned it, then checked the oil level; finding it below 1/3 of the mark, we immediately added oil of the same grade. After turning on the power switch and attempting to start the device, knocking noises were still heard. Later, the components of the motion mechanism—the crankshaft, connecting rods, pistons, and cylinders—were taken apart one by one for inspection, and it was found that the crankshaft had cracks; it was obvious that it was on the verge of breaking, likely due to a lack of oil for some time already. Due to a lack of oil, the moving parts experience dry friction, and excessive loading causes varying degrees of damage to these parts. We cleaned and ground the various moving parts that were damaged, replaced those that were severely damaged, then reinstalled them and tested the machine. The knocking sound disappeared, and the displacement returned to normal. It is clear that engine oil is absolutely essential; otherwise, there will be serious consequences. 2. Poor tightness of the air silencing filter and air valves: The reduction in exhaust volume is also related to the tightness of the air silencing filter and air valves. The air silencing filter must be cleaned regularly. Cleaning the dirt on the valve plates and valve discs helps the air compressor maintain a proper exhaust volume. Under normal conditions, the filter should be cleaned every 200 hours, and the air valve should be cleaned every 500–800 hours. 3. Poor quality of lubricating oil: Low-quality lubricating oil can cause the piston rings to be stuck, thereby reducing the exhaust volume. Therefore, high-quality lubricating oil should be selected. After long-term use, the lubricant will contain impurities and dust, so it also needs to be filtered. Generally, the engine oil should be replaced every 500 to 800 hours, and the oil used previously should be filtered. 4. Excessively high exhaust temperature: An excessively high exhaust temperature can also cause the piston rings to be stuck, resulting in a decrease in exhaust volume. Lowering the temperature will solve the problem. Two points need attention here: (1) The ambient temperature should not be too high, generally not exceeding 40°C. (2) If the gas valve leaks, the high-temperature gas discharged will return to the cylinder. At this point, we should carefully inspect the air valve, grind the valve plate, or replace the valve element in order to eliminate air leaks; only then can the problem of excessively high temperatures be resolved. IV. Causes of freezing issues and countermeasures: Air compressors can also experience “freezing” problems during operation. The reasons that cause air compressors to \"freeze\" can be attributed to both electrical and mechanical factors. 1. Electrical reasons: The electrical part of an air compressor mainly consists of a motor, an air pressure automatic switch, etc. When the air compressor is operating normally, the pressure switch is closed. When the pressure in the air reservoir reaches the rated discharge pressure, the compressed air pushes against the rubber element, causing the spring to move via the bridge mechanism; this in turn separates the moving contact from the stationary contact inside the bakelite housing, breaking the circuit and stopping the motor from rotating. Conversely, when the pressure in the air tank drops to a certain level, the spring rebounds, the circuit is connected, and the motor starts to operate. If the coil of contactor C is not powered, the pneumatic switch cannot function, resulting in a \"freeze\" condition. For example, when a phase is missing, the power switch K cannot close, and coil C does not receive power, resulting in a \"freeze\" condition. 2. Mechanical reasons: The mechanical causes of a \"freeze\" include broken connecting rods, pistons stuck in the cylinders, and excessive or insufficient clearance between the piston and the cylinder. Rod breakage is mostly related to overloading, so overloading should be avoided to prevent rod breakage. At the same time, attention should be paid to the assembly clearance of the cylinder and piston as well as their lubrication condition. Additionally, when the air compressor is shut down and not in use, the drain valve at the bottom of the air tank should be opened to release the wastewater. If not used for an extended period, care should be taken to prevent moisture from entering, keep the air valves and oil seals clean, apply oil to the open surfaces of the cylinder, piston, etc., and seal them with oil-paper. In short, to ensure the proper operation of the compressor and extend its lifespan, regular maintenance is extremely important. At the same time, it is required that maintenance workers have a strong sense of responsibility in order to detect and fix faults as early as possible. Cutting machine failures and blade sharpening: Some minor issues that arise during cutting due to the blades often leave operators confused and unable to identify the problem. The following points are provided for reference by colleagues. Fault 1: The newly sharpened blade is put into use, and although it does not come into contact with any hard objects during cutting, a part of the blade edge suddenly breaks off. The main reason for this problem is an improper control of the feed rate during grinding (the feed rate being too high), which leads to excessively high temperatures during grinding (that is, high temperatures at the point where the blade contacts the grinder wheel), thereby \"damaging\" the blade. Fault 2: The cutting blade does not reach the bottom during cutting. This is mainly due to the out-of-tolerance straightness of the blade edge. Fault 3: Shortly after the blade has been sharpened and is used for cutting, the cut surface of the paper shows blade marks, or poor cutting quality occurs during the cutting process. This is mainly due to overheating during sharpening, which makes the blade too soft.