Detection of incipient cavitation in pumps using acoustic emission

This work concerns the detection of incipient cavitation in pumps using acoustic emission (AE). Three activities have been pursued in this context: (a) the construction of a small-scale rig for the investigation of cavitation detection using AE sensors; (b) the acquisition of data on a 75 kW single-stage centrifugal pump in an industrial test loop under normal running and cavitation conditions; (c) the determination of parameters that could be used for the early diagnosis of cavitation within pumps. In the laboratory-scale apparatus water was pumped around a short loop by a 3 kW centrifugal pump. The flow loop contained a section specifically designed to induce cavitation by means of reducing the pressure level to that of the vapour pressure of the fluid. This apparatus was used to produce a variety of well-controlled cavitation conditions which were useful in determining the suitability of AE for the detection of cavitation. The industrial-scale tests consisted of progressively reducing the net positive suction head in a 75 kW pump while recording the AE signals at various points on the test loop and pump. Results are presented from both laboratory and full-scale tests which demonstrate the feasibility of detecting incipient cavitation using AE in the face of background noise from normal running of the pump. The features of AE which are indicative of cavitation are also seen to change continuously as NPSH is decreased. Thus early detection of cavitation is possible, certainly before any indication is seen on the dynamic head.