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Surge in centrifugal compressors: When the flow rate through the compressor becomes low enough, severe rotational stall occurs throughout the diffuser channel. This leads to a sudden drop in the pressure at the compressor outlet, causing the pressure in the pipeline network to become higher than that at the compressor outlet. As a result, the airflow is forced to flow back into the compressor, until the pressure in the pipeline network drops below that at the compressor outlet, after which the compressor resumes supplying air to the pipeline network and returns to normal operation. When the pipeline pressure returns to its original level, the flow rate remains below the surge flow rate; the compressor suffers from severe rotational stall again, the outlet pressure drops, and the airflow in the pipeline flows back into the compressor. This cycle repeats itself, causing periodic and significant fluctuations in the compressor’s flow rate and outlet pressure, which in turn leads to severe air flow fluctuations in the compressor; this phenomenon is known as compressor surge. Generally, the larger the capacity of the piping network, the greater the surge amplitude and the lower the frequency; conversely, the smaller the capacity of the piping network, the smaller the surge amplitude and the higher the frequency. 1. Characteristics of compressor surge: (1) The compressor operation is extremely unstable; the outlet pressure and inlet flow rate of the compressed gas fluctuate significantly on a periodic basis at a low frequency, while the average exhaust pressure decreases. (2) Surge is characterized by intense periodic airflow noise, with a howling sound from the airflow. (3) Vibration of the airflow in the unit occurs, with a sharp increase in the amplitude of vibration in the machine body, bearings, and pipelines. Due to intense vibration, the liquid lubrication conditions of the bearings are disrupted, damaging the bearing bushings. Friction and collisions can occur between the rotor and the stator. The sealing element will be severely damaged. 2. Conditions to prevent surge in centrifugal compressors: (1) Prevent low inlet pressure, high inlet temperature, and a decrease in the molecular weight of the gas. (2) Prevent blockages in the pipeline network from causing changes in the pipe’s properties. (3) During startup and shutdown, the speed should not be increased or decreased too rapidly; speed should be increased first before voltage is increased, and voltage should be decreased first before speed is decreased. (4) Operate the anti-surge valve slowly and smoothly when opening or closing it. When closing the anti-surge valve, start with low pressure and then high pressure; when opening it, start with high pressure and then low pressure. If surge occurs, all anti-surge valves should be opened immediately to increase the compressor flow rate, and then appropriate actions should be taken in accordance with the situation, following standard procedures.