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A compressor is a machine used to increase gas pressure and transport gases. From an energy perspective, a compressor is a machine that converts the mechanical energy of a prime mover into gas pressure energy. With the advancement of science and technology, the application of pressure energy has become increasingly widespread, making compressors one of the essential key devices in many sectors of national economic development. During operation, compressors are bound to experience some faults, or even accidents. A fault refers to an abnormal condition that occurs during the operation of the compressor; once it is resolved, the compressor can return to normal operation. An accident, on the other hand, refers to a situation in which damage occurs. The two are often related; if a fault is not resolved in a timely manner, it can lead to serious accidents. 1. Common faults, their causes, and corrective measures: Insufficient displacement: Insufficient displacement is determined in relation to the designed displacement of the compressor. It can mainly be considered from the following aspects: 1. Fault of the intake air filter: Accumulated dirt causes blockages, reducing the exhaust volume ； The intake pipe is too long and has too small a diameter, which increases the suction resistance and affects the volume of air drawn in; the filter needs to be cleaned regularly. 2. A decrease in the compressor speed leads to a reduction in the volume of air discharged: When an air compressor is used improperly, its discharge capacity is designed based on certain altitude levels, suction temperature, and humidity. When it is used in high-altitude areas that exceed these standards, factors such as a lower suction pressure result in a decrease in the volume of air discharged. 3 The cylinders, pistons, and piston rings are severely worn and out of specification, which increases the relevant clearances and the leakage volume, thereby affecting the exhaust volume. During normal wear, it is necessary to replace wear-prone parts such as piston rings in a timely manner. When the issue is due to incorrect installation or inappropriate clearance, corrections should be made in accordance with the drawings; if no drawings are available, empirical data can be used. For the circumferential clearance between the piston and the cylinder, in the case of cast-iron pistons, the clearance value should be between 0.06/100 and 0.09/100 of the cylinder diameter ； For aluminum alloy pistons, the clearance is 0.12/100 to 0.18/100 of the gas diameter ； The steel piston value can be taken as the lower value of the aluminum alloy piston value. 4 Poor sealing of the stuffing box causes air leakage, reducing the gas volume. The primary reason is that the stuffing box itself was not manufactured to the required standards ； Secondly, it may be due to poor alignment between the piston rod and the stuffing box during installation, which leads to wear and tearing and thus air leakage ； Lubricating oil is generally added at the stuffing box, where it serves to lubricate, seal, and cool. 5 The impact of faults in the compressor’s suction and exhaust valves on the exhaust volume. Metal fragments or other debris falling between the valve seat and the valve disc result in poor sealing, causing air leakage. This affects not only the displacement but also the changes in interstage pressure and temperature ； Leakage occurs due to a poor fit between the valve seat and the valve disc, which affects the exhaust volume. One reason is a manufacturing defect, such as warping of the valve disc; the other reason is leakage resulting from severe wear between the valve seat and the valve disc. The spring force of the 6-valve mechanism is not well matched with the gas force. Excessive elasticity causes the valve disc to open slowly, while too weak elasticity results in the valve disc not closing promptly. These issues not only affect the volume of air flow but also impact power output, as well as the lifespan of the valve disc and springs. At the same time, it will also affect changes in gas pressure and temperature. 7 The clamping force of the air valve is inappropriate. If the clamping force is too low, air leakage will occur; on the other hand, if it’s too high, it can cause the valve cover to deform or get damaged. The clamping force can generally be calculated using the formula: p = kπ/4 D²P², where D is the diameter of the valve chamber, P₂ is the maximum gas pressure, and K is a value greater than 1, typically ranging from 1.5 to 2.5. For low pressures, K = 1.5 to 2.0, while for high pressures, K = 1.5 to 2.5. Choosing K in this way has proven to be effective in practice. If the air valve malfunctions, the valve cover will inevitably heat up, and the pressure will also be abnormal. 2. Abnormal exhaust temperature: An abnormal exhaust temperature refers to a value that is higher than the design value. Theoretically, the factors that affect an increase in exhaust temperature include intake air temperature, pressure ratio, and compression index (for air, the compression index is K=1.4). Factors that affect the high intake temperature in practice include low intercooler efficiency, or excessive scale buildup in the intercooler, which hinders heat exchange; as a result, the intake temperature in subsequent stages necessarily rises, and so does the exhaust temperature. Air leakage in the valve and piston rings not only leads to an increase in exhaust temperature but also causes changes in the pressure between stages; whenever the pressure ratio is higher than normal, the exhaust temperature rises. Furthermore, in water-cooled machines, a lack of water or insufficient water volume will cause the exhaust temperature to rise. 3. Abnormal pressure and reduced exhaust pressure: If the volume of air discharged by the compressor at the rated pressure does not meet the user’s flow requirements, then the exhaust pressure will inevitably decrease. The decrease in exhaust pressure is merely a symptom; the real issue is that the volume of air discharged is not sufficient to meet the user’s needs. At this point, it is necessary to use another machine with the same exhaust pressure but a larger displacement. The main reasons for abnormal inter-stage pressure are air leakage from the valves or leakage due to worn piston rings; therefore, it is necessary to look for causes in these areas and take corresponding measures. 4. Abnormal noises: If certain components of the compressor fail, it will emit abnormal noises; generally, operators are able to identify such abnormal noises. The gap between the piston and the cylinder head is too small, resulting in direct collision ； Loose or detached nuts connecting the piston rod to the piston, damaged thread plugs on the piston’s end face, the piston moving upward and hitting the cylinder head, metal fragments falling into the cylinder, as well as water accumulation within the cylinder – all of these can cause knocking sounds inside the cylinder. Loosening, detachment, or breaking of the crankshaft bearing bolts and nuts in the crankcase, as well as of the connecting rod bolts and crosshead bolts; severe wear of the shaft diameter leading to increased clearance; excessive clearance or severe wear between the crosshead pin and its bushing – all of these can cause knocking sounds inside the crankcase. A broken exhaust valve disc, a soft or damaged valve spring, or an improperly adjusted load regulator can all cause knocking sounds inside the valve chamber. Use this to identify the fault and take corrective actions. 5. Overheating fault: When the temperature at points of friction such as the crankshaft and bearings, the crosshead and slide plates, as well as the packing and piston rod, exceeds the specified value, it is referred to as overheating. The consequences of overheating are: first, it accelerates the wear between the friction pairs; second, the excess heat keeps accumulating until it burns the friction surfaces and causes severe damage to the machine. The main causes of bearing overheating are: uneven fit between the bearing and the journal, or too small a contact area ； Bearing misalignment, crankshaft bending, torsion ； Too low viscosity of the lubricating oil, blockages in the oil passages, and faults in the oil pump that cause a lack of oil supply, etc ； During installation, leveling was not done, the gaps were not properly adjusted, the main shaft and the motor shaft were not aligned, and there was tilting between the two shafts. 6. Compressor accidents – Fracture accidents: Crankshaft fracture: Such fractures mostly occur at the transition zone between the shaft journal and the crank arm’s rounded corners. The main reasons for this are as follows: the transition radius is too small (r refers to the crankshaft journal) ； During heat treatment, the rounded corners were not treated, resulting in stress concentration at the junctions ； The corner rounding is irregular, with sudden changes in the local cross-section ； Prolonged overloading, along with some users arbitrarily increasing the speed in order to boost output, leads to an improved stress condition ； The material itself has defects, such as sand holes and shrinkage cavities in castings. Furthermore, breakage caused by cracking at the oil holes on the crankshaft can also be observed. Breakage of the connecting rod: There are several scenarios: the connecting rod screw breaks, and the reasons for this include plastic deformation occurring as a result of long-term use of the connecting rod screw ； Poor contact between the screw head or nut and the large-end surface creates an eccentric load; this load can be as much as seven times greater than the axial force acting on the bolt. Therefore, any slight misalignment is not allowed – the contact must be even, and the maximum distance at which the contact points are separated must not exceed 1/8 of the circumference, that is, 450 ； There are issues with the processing quality of the bolt material. Piston rod fracture: The main areas where fractures occur are at the threads connecting to the crosshead and at the threads used to secure the piston; these two points represent the weak spots of the piston rod. Fractures tend to happen frequently due to design flaws, careless manufacturing practices, or operational issues. If there are no issues with the design, manufacturing, or material quality, the preload during installation should not be too high; otherwise, when the maximum force reaches the yield limit, the piston rod will break. After prolonged operation, due to excessive wear of the cylinders, the pistons in the horizontal row may sink. This creates additional loads on the connecting threads; continued operation could potentially lead to the breakage of the piston rods. This aspect requires special attention during maintenance. Furthermore, if the piston rod is subjected to a severe impact due to damage in other areas, it is possible for the piston rod to break. Cracking of cylinders and cylinder heads: Main cause – In water-cooled machines, if it is forgotten to drain the cooling water from the cylinders and cylinder heads after shutting down the machine in winter, the cooling water will freeze and cause the cylinders and cylinder heads to crack. This is especially true in the northern regions of China, where it is necessary to drain the cooling water after shutting down the machine ； The water supply was interrupted during operation and not detected in time, which caused the cylinder temperature to rise; the sudden introduction of cooling water then led to the cylinder bursting ； Reasons such as an excessively small dead center clearance, loose piston nuts, metal debris falling into the cylinder, and the removal of the plug on the piston can all cause the piston to strike the cylinder head and cause it to crack. 7. Combustion and explosion accidents: Oil-lubricated compressors often suffer from carbon buildup, which is something we do not want. Carbon buildup can cause piston rings to get stuck in their grooves, disrupt the proper functioning of air valves, and reduce the area of the airflow channels thereby increasing resistance. Under certain conditions, this carbon buildup can catch fire, leading to explosions in the compressor. Therefore, not too much lubricating oil should be supplied to the cylinder. Gases that are not properly filtered and contain a large amount of dust must not be allowed to enter the cylinder; otherwise, carbon deposits may form, and contact between these deposits and gases rich in volatile substances could lead to an explosion. To prevent fires and explosions, it is essential to plan regular maintenance and clean the oil deposits in the gas storage tanks and pipelines on a periodic basis. In addition, the following operational factors can also cause combustion and explosion accidents in compressors: an explosion occurs because air is not thoroughly expelled using low-pressure nitrogen before the compressor is tested under hydrogen, oxygen, or hydrogen-nitrogen load conditions. Due to a lack of operational knowledge, after starting the engine, the valve from the compressor to the air tank was not opened, causing the exhaust pressure to rise sharply and resulting in an explosion. Therefore, to prevent such accidents, it is necessary to be familiar with the operating procedures before driving, and after starting the vehicle, to pay close attention to the readings on the pressure gauge. In general small and medium-sized compressors, it is advisable to remove the gate valve from the pipeline from the compressor to the air tank, leaving only a check valve. Furthermore, compressor operators should receive training before taking up their duties. Due to the poor sealing of the gas valves in the high-pressure stage of the compressor, high-pressure and high-temperature gas returns to the cylinder, causing high temperatures near the exhaust valve; when carbon deposits are present, this can lead to an explosion. To avoid accidents, it is necessary at this time to service the exhaust valve, check for air leaks, and eliminate the faults.