Torsion Vibration Calculation in Recipracating Compressors

The trend in the development of compressor trains is that manufacturers are striving to increase its capacity while reducing the mass-dimensional parameters of the machine and maintaining its reliability. One of the main way to raise the capacity of a reciprocating compressor unit is to increase the shaft speed. However, as the speed increases, the risk of torsion vibration appears. The resulting torsion vibration is the reason of an additional source of noise, and also cause additional dynamic loads that reduce the life of the crankshaft and may lead to its breakdown. Furthermore, crankshaft failure can cause breakdown of other parts of the compressor unit such as bearings, crosshead, piston and etc. Additionally, the large generated peak torques can overload components such as gears, splines, and couplings. Accordingly, a thorough torsion vibration analysis should be included as an integral part of the reciprocating compressor design process. This paper presents main stages of torsion vibration calculation in a multi-row reciprocating compressor including natural and forced vibration analysis. General rules of modeling an equivalent torsion system, natural frequencies calculation by Holzer's method and matrix-eigenvalue method, evaluation of operation mode of a compressor unit by Campbell diagram, harmonic analysis of the torque, determination of the vibration amplitudes and additional stress caused by torsion vibration are described in this work.