Pulsation, Vibration, And Noise Issues With Wet And Dry Screw Compressors

Proceedings of the Fortieth Turbomachinery Symposium, September 12-15, 2011, Houston, Texas (Turbomachinery Laboratory, Texas A&M University)
Pulsation, Vibration, And Noise Issues With Wet And Dry Screw Compressors
Donald R. Smith, Senior Staff Engineer
Engineering Dynamics Incorporated, San Antonio, TX USA
ABSTRACT
Wet (oil injected) and dry (oil free) screw compressors are widely used in many applications.  Limited information is available regarding the pulsation, vibration, and noise problems associated with these types of compressors, however. The tutorial discusses such problems, including case histories where field testing was performed, and provides design recommendations.
Both wet and dry screw compressors normally generate pulsation at the pocket passing frequency (PPF) and its multiples. The pulsation amplitudes are affected by many variables such as mole weight of the gas, operating pressures, speed, screw profile, and shape of the discharge port. The pulsation amplitudes are further amplified by acoustical natural frequencies of the compressor/silencer/piping system.
Dry screw compressors are generally supplied with suction and discharge silencers which are designed to attenuate the pulsation generated by the compressors. Most of the silencers are reactive type (Helmholtz filters), absorptive type, or a combination of these two. Although the silencers are designed to attenuate pulsation at certain frequencies, they can also amplify pulsation when the excitation frequencies are coincident with the acoustical natural frequencies of the silencer itself. Pulsation in the silencers can also increase the vibration levels of the compressor rotors and can cause electrical problems to be fed into the local bus.
Consequently, silencers should be carefully designed to attenuate the pulsation levels over a wide frequency band.
Free Full Text Source: http://turbolab.tamu.edu/uploads/tproc/PDFs/PulsationVibrationAndNoise.pdf