The non-intrusive detection of incipient cavitation in centrifugal pumps

This thesis investigates methods for the detection of incipient cavitation in centrifugal pumps. The thesis begins by describing the working of the centrifugal pump which makes this type of pump particularly prone to cavitation. The basic mechanisms of cavitation are described, which explain why this phenomenon is so damaging. The thesis reports the results of experiments to predict the onset cavitation using a range of statistical parameters derived from: the vibration signal obtained from an accelerometer on the pump casing, the airborne acoustic signal from a microphone close to the outlet of the pump and the waterborne acoustic signal from a hydrophone in the outlet pipe close to the pump. An assessment of the relative merits of the three methods for the detection of incipient cavitation is given based on a systematic investigation of a range of statistical parameters from time and frequency domain analysis of the signals. It is shown that is the trends in the features extracted are more than their absolute values in detecting the onset of cavitation. A number of recommendations are made as to which features are most useful, and how future work incorporating these suggestions could give a powerful method for detecting incipient cavitation. A major contribution of this research programme is the development of a novel capacitive method for the detection of cavitation. Some basic theory is presented to show the principles of the device and then the details of its construction and placement in the test rig built for the purpose. The data for the tests using the capacitive sensor are given and we can say definitely that it has been confirmed as a method of detecting cavitation in a pipe system, and that it is a promising method for the detection of the onset of cavitation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Early Failure Detection and Diagnostics of High Speed Self Aligning Journal Bearing

Because of their high load carrying capacity and low cost, journal bearings are widely used to support the rotor of industrial machinery with high loads, such as steam turbines, centrifugal compressors and pumps. However, sudden catastrophic failure journal bearings can result in huge economic loss and high safety problems. It is necessary to develop effective condition monitoring technologies to detect and diagnose the failures at early stage and avoid such catastrophic failure. Previous researchers have studied the low frequency vibration characteristics as well as the high frequency vibration and acoustics emission for the early detection of journal bearing failure. However, these studies give relatively little information to the vibro-acoustic characteristics of high speed self aligning journal bearings. This paper focuses on the condition monitoring of high speed self aligning journal bearings through vibro-acoustic analysis

Diagnosis of Centrifugal Pump Faults Using Vibration Methods

Pumps are the largest single consumer of power in industry. This means that faulty pumps cause a high rate of energy loss with associated performance degradation, high vibration levels and significant noise radiation. This paper investigates the correlations between pump performance parameters including head, flow rate and energy consumption and surface vibration for the purpose of both pump condition monitoring and performance assessment. Using an in-house pump system, a number of experiments have been carried out on a centrifugal pump system using five impellers: one in good condition and four others with different defects, and at different flow rates for the comparison purposes. The results have shown that each defective impeller performance curve (showing flow, head, efficiency and NPSH (Net Positive Suction Head) is different from the benchmark curve showing the performance of the impeller in good condition. The exterior vibration responses were investigated to extract several key features to represent the healthy pump condition, pump operating condition and pump energy consumption. In combination, these parameter allow an optimal decision for pump overhaul to be made [1]

Prediction of metal pm emission in rail tracks for condition monitoring application

Exposure to particulate material (PM) is a major health concern in megacities across the world which use trains as a primary public transport. PM emissions caused by railway traffic have hardly been investigated in the past, due to their obviously minor influence on the atmospheric air quality compared to automotive transport. However, the electrical train releases particles mainly originate from wear of rails track, brakes, wheels and carbon contact stripe which are the main causes of cardio-pulmonary and lung cancer. In previous reports most of the researchers have focused on case studies based PM emission investigation. However, the PM emission measured in this way doesn’t show separately the metal PM emission to the environment. In this study a generic PM emission model is developed using rail wheel-track wear model to quantify and characterise the metal emissions. The modelling has based on Archard’s wear model. The prediction models estimated the passenger train of one set emits 6.6mg/km-train at 60m/s speed. The effects of train speed on the PM emission has been also investigated and resulted in when the train speed increase the metal PM emission decrease. Using the model the metal PM emission has been studied for the train line between Leeds and Manchester to show potential emissions produced each day. This PM emission characteristics can be used to monitor the brakes, the wheels and the rail tracks conditions in future

The Non-intrusive Detection of Incipient Cavitation in Centrifugal Pumps

This thesis investigates methods for the detection of incipient cavitation in centrifugal pumps. The thesis begins by describing the working of the centrifugal pump which makes this type of pump particularly prone to cavitation. The basic mechanisms of cavitation are described, which explain why this phenomenon is so damaging. The thesis reports the results of experiments to predict the onset cavitation using a range of statistical parameters derived from: the vibration signal obtained from an accelerometer on the pump casing, the airborne acoustic signal from a microphone close to the outlet of the pump and the waterborne acoustic signal from a hydrophone in the outlet pipe close to the pump. An assessment of the relative merits of the three methods for the detection of incipient cavitation is given based on a systematic investigation of a range of statistical parameters from time and frequency domain analysis of the signals. It is shown that is the trends in the features extracted are more than their absolute values in detecting the onset of cavitation. A number of recommendations are made as to which features are most useful, and how future work incorporating these suggestions could give a powerful method for detecting incipient cavitation. A major contribution of this research programme is the development of a novel capacitive method for the detection of cavitation. Some basic theory is presented to show the principles of the device and then the details of its construction and placement in the test rig built for the purpose. The data for the tests using the capacitive sensor are given and we can say definitely that it has been confirmed as a method of detecting cavitation in a pipe system, and that it is a promising method for the detection of the onset of cavitation

The monitoring of cavitation in centrifugal pumps based on the analysis of vibro-acoustic measurements

Cavitation in centrifugal pumps causes damages to pump components and produces high levels of vibration and noise, which not only reduces pump performance but also consumes additional energy. Unfortunately, many pumps operate under a certain degree of cavitation for a number of reasons such as varying operating conditions, inadequate installation and harsh environments. To evaluate the degree of cavitation online and to take necessary actions at an early stage, this research focuses on developing a cavitation measurement technique using non-intrusive vibro acoustic techniques. In this paper, conventional vibro-acoustics measurements are examined with different dimensionless parameters for characterizing the signals and hence for cavitation diagnosis. Conventional parameters such as peak factors and kurtosis from both the time domain and frequency domain have been evaluated to be inefficient for indicating cavitation in different stages. However, the spectral entropy has been found to be more accurate in presenting the cavitation. Especially, the spectral entropy from airborne acoustics can yield a better diagnostic result than the surface vibration

A clamping force measurement system for monitoring the condition of bolted joints on railway track joints and points

Many industrial structures associated with railway infrastructures rely on a large number of bolted joint connections to ensure safe and reliable operation of the track and trackside furniture. Significant sums of money are spent annually to repair the damage caused by bolt failures and to maintain the integrity of bolted structures. In the UK, Network Rail (the organization responsible for rail network maintenance and safety) conducts corrective and preventive maintenance manually on 26,000 sets of points (each having approximately 30 bolted joints per set), in order to ensure operational success and safety for the travelling public. Such manual maintenance is costly, disruptive, unreliable and prone to human error. The aim of this work is to provide a means of automatically measuring the clamping force of each individual bolted joint, by means of an instrumented washer. This paper describes the development of a sensor means to be used in the washer, which satisfies the following criteria. 1. Sense changes in the clamping force of the joint and report this fact. 2. Provide compatibility with the large dynamic range of clamping force. 3. Satisfy the limitations in terms of physical size. 4. Provide the means to electronically interface with the washer. 5. Provide a means of powering the washer in situ. 6. Provide a solution at an acceptable cost. Specifically the paper focuses on requirements 1, 2 and 3 and presents the results that support further development of the proposed design and the realization of a pre-prototype system. In the paper, various options for the force sensing element (strain gage, capacitor, piezo-resistive) have been compared, using design optimization techniques. As a result of the evaluation, piezo-resistive sensors in concert with a proprietary force attenuation method, have been found to offer the best performance and cost trade-off The performance of the novel clamping force sensor has been evaluated experimentally and the results show that a smart washer can be developed to monitor the condition of bolted joints as found on railway track and points

Prediction of metal pm emission in rail tracks for condition monitoring application

Exposure to particulate material (PM) is a major health concern in megacities across the world which use trains as a primary public transport. PM emissions caused by railway traffic have hardly been investigated in the past, due to their obviously minor influence on the atmospheric air quality compared to automotive transport. However, the electrical train releases particles mainly originate from wear of rails track, brakes, wheels and carbon contact stripe which are the main causes of cardio-pulmonary and lung cancer. In previous reports most of the researchers have focused on case studies based PM emission investigation. However, the PM emission measured in this way doesn’t show separately the metal PM emission to the environment. In this study a generic PM emission model is developed using rail wheel-track wear model to quantify and characterise the metal emissions. The modelling has based on Archard’s wear model. The prediction models estimated the passenger train of one set emits 6.6mg/km-train at 60m/s speed. The effects of train speed on the PM emission has been also investigated and resulted in when the train speed increase the metal PM emission decrease. Using the model the metal PM emission has been studied for the train line between Leeds and Manchester to show potential emissions produced each day. This PM emission characteristics can be used to monitor the brakes, the wheels and the rail tracks conditions in future

Monitoring Cavitation in Centrifugal Pumps using a Noninvasive Capacitance Sensor

Cavitation in centrifugal pumps damages pump components, reduces delivery performance and consumes additional energy. This paper presents a novel non-invasive method based on capacitance measurement techniques for detecting and diagnosing cavitation in a centrifugal pump. Two cylindrical metal plates placed on the external wall of non-conductive pipe in the discharge line constitute the two electrodes of the capacitive sensor. The electrode plates and the pipe wall can be modeled electrically using a RLC circuit. The frequency shift of the circuit at resonance due to dielectric changes of different air to water ratios is measured to quantify the level of cavitation. Test results have shown that the frequency shifts can be as high as 200kHz with only a small amount of bubbles induced in the flow. The frequency shifts exhibit a nonlinear increasing behavior but give a good indication of the onset of cavitation and different levels of cavitation activity