Screw Pass Frequency for a Screw Type Compressor

Screw Pass frequency (SPF)

We often find screw type compressors, in the example below we collect vibration data transiently (from shutdown-startup-load-full load-unload) until shutdown again

From the field data, the sound of the compressor sounds roughness when compared to other similar equipment. From the data, several findings or indications were obtained:
1. Transient waveform data clearly shows the difference in amplitude
between load, full load and no load
2. Spectrum at load has a higher amplitude and dominant harmonic SPF
(screw pass frequency)

There may be indications of looseness in the internal rotating compressor, bearings or screw parts that have loosened

Those who have experience with high vibration problems in screw compressors, please share your experiences, thanks