Abstract: Aiming at vibration problem on air-conditioner pipeline, it discussed the influence of pipeline modality by suction and exhaust pressure of the pipe on the air-conditioner. The result indicates that when considering the suction and discharge pressure, the natural frequencies of the pipeline with the same vibration characteristic increase correspondingly, that is pre-stress enhances stiffness of the pipeline; If the suction and discharge pressure of pipeline are not considered in pipeline modality analysis. it would miss some natural frequencies and misleading the pipeline improvement directions.

Key words: Pre-pressure, Fluid-structure coupling, Pipeline modality