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As the operating time of the screw air compressor increases, the bearings within the main unit inevitably wear out, which in turn leads to axial movement and increased radial displacement of the screw rotors. Such changes result in alterations in the gaps between the screw rotors themselves, as well as between the screw rotors and the main unit’s housing and its front and rear end surfaces. These variations in clearance are normal throughout the bearing’s service life, and the resulting decline in the air production capacity of the screw air compressor as well as the increased load on the main motor are also normal. As the operating time of the screw air compressor gradually approaches the scheduled major maintenance period for the main unit, the lifespan of its bearings approaches the maximum allowable limit. At this point, the axial and radial displacement of the screw rotor also approaches the maximum design limits. Such changes cause significant variations in the gaps between the screw rotors, as well as between the screw rotors and the main housing as well as the front and rear end surfaces. At this point, although the host is still running safely, it is time to consider planning a major overhaul for it. Once the operating time of the unit exceeds the period required for major maintenance, bearing wear and the clearance between the components of the machine reach the limits permitted by its technical specifications. At this point, the machine is in an unsafe operating condition, and serious consequences may occur at any time: 1. The exhaust volume of the air compressor will decrease significantly: An increased clearance between the machine’s components leads to a sharp drop in its efficiency, resulting in a significant reduction in the air compressor’s exhaust volume, which in turn affects the normal production processes of the organizations that rely on this air supply. Especially for those users whose air compressor capacity is not significantly excessive, as the output of the air compressors decreases, and given that the demand for air in the systems using it remains relatively stable, the pressure of compressed air in the piping network drops considerably. This can result in the equipment in those systems failing to operate properly or even stopping completely, thereby affecting the normal production of the facility or causing temporary shutdowns that incur losses for the company. 2. The operating load on the main machine increases, posing a risk to the main motor and electrical systems: Intense friction that can occur between the screw rotor and the other components of the main machine, as well as between the screw rotor and the front and rear end surfaces, as well as between the screw rotor and the main machine housing, can lead to a sharp increase in the operating load of the main machine. Additionally, bearings that are severely worn also generate high operating loads. As a result, the motor will be operating under overload conditions, which can seriously compromise its safe operation. In severe cases, if the electrical protection devices of the air compressor unit are not sensitive enough or fail to function properly, it can also lead to motor burnout. 3. Sudden locking of the motor: When this occurs, if the electrical protection system does not respond in time or fails to function properly, it can also cause serious damage to the main motor and the electrical system. Regarding the handling of a ‘stuck’ main unit, on the one hand, the repair costs for a major overhaul will be much higher than those for a regular overhaul; on the other hand, since the components of the main unit are damaged, its overall performance after repair will also be lower compared to that of a main unit that has undergone a regular overhaul. If the damage to the host is severe to the point where it has no value for repair or cannot be repaired at all, the only option is to discard it and replace it with a new one, resulting in the greatest possible loss. The cost of purchasing a new compressor unit is usually around one-third of the cost of buying an entire air compression system, which is far higher than the cost of routine maintenance for the compressor. In normal circumstances, the overall technical performance of a compressor that has undergone proper maintenance is very similar to that of a new one! In summary, routine maintenance of compressors is not only a basic requirement for equipment upkeep but also essential for companies to control their maintenance costs, avoid unnecessary financial losses, and ensure uninterrupted production. Therefore, it is necessary to carry out regular maintenance on compressor units in accordance with established standards. So, how can one determine when a screw compressor unit needs maintenance? Precisely speaking, the time for maintenance should be determined based on the lifespan of the bearings. However, it’s difficult to have accurate indicators to determine whether the bearing lifespan is about to expire or has already expired. As a result, leading international compressor manufacturers, drawing on their nearly century-long experience, have established a standard of performing maintenance on compressors after 20,000 hours of operation or after 4 years.