Monitoring of Screw Compressor Bearings and Rotational Elements

Introduction

Monitoring screw compressors can be very different from monitoring other types of equipment, such as pumps, fans and motors. The primary difference is the extremely high noise level caused by the gas
pulse that is generated as the compressed gasses are discharged from the unit. This is compounded if the unit is a two-stage compressor with two discharge gas pulses. The gas pulse frequency will be equal to the female rotor speed (or speeds), and enveloped acceleration amplitudes will be high. Under normal operating conditions, amplitudes in excess of 15 gE have been observed.

Two techniques may be used to help prevent overlooking these “hidden” enveloped acceleration amplitudes. The first, and easiest, is to use the Frequency Analysis Module (FAM) and assign the installed
bearing’s fault frequencies to the measurement POINT. When data is collected, overlay the FAM markers on the spectrum, regardless of how the spectrum looks, and look for energy spikes at the marker
positions.  The second technique will provide you with the same information in a different way, but will allow you to alarm on the bearing fault frequencies more easily.

This application note provides detailed instructions on how to carry out both techniques.