1、- 1 - 原文 Solving Vibration Problems In Hydraulic Machinery Abstract In the current paper, various cases of vibration problems detected in hydraulic machinery are presented.These cases were found during several years of vibration monitoring.the problems have been classified depending on their origin.
2、For all of them,a systematic approach is given indicating the symptoms,the exciatation provoking them,the possibilities of amplification due to resonance and the remedies that have been applied. Introduction Vibration problems are common in hydraulic machinery.Solving them helps to increase the mach
3、ine life and to reduce maintenance costs. Many cases have been found and solved during last years of monitoring (Egusquiza 1998 and Egusquiza et.2000).Some of them have been due to design or mounting problems and others due to damage in machine elements.The cases presented here correspond to large m
4、achine with vertical shaft and rigid coupling.The problems found have been classified in the following types: Type 1: Excessive excitations of hydraulic origin Type 2: Hrust bearing problems Type 3: Unbalance and misalignment Type 4: Electromagnetic problem A methodology to solve these types of vibr
5、ation problems is proposed in the paper.The steps to follow are indicated in Fig,1.Once the abnormal high vibration amplitudes have been detected through scheduled monitoring or machine malfunctioning.Vibration analysis has to be proformde to identify the origin of the exciation provoking them.Vario
6、us techniques are available - 2 - depending on the type of excitation under consideration,whether it is hydraulic,mechanic or Eletromagnetion. The resulting high vibration levels may also be due to some type of resonace in the hydraulic system or in the mechanical compoents.Therefore, this possibili
7、ty must be checed before a correct diagnostic can be made. Finally, remedies to the probiem are proposed and their success is confirmed comparing the vibrations after the modification with theprevious ones. Type 1: Excessive Hydraulic Excitation. Typical vibrations of hydraulic origin are generated
8、by rotor-stator interaction (RSI) and by cacitation. RSI is due to the interference between the runner blades and guide vanes.It can generate pressure pulsations of high amplitude in hydraulic machines.As a result,cracks in runners and excessive vibrationlevels in machine and piping can be produced.
9、RSI identification is normally easy with spectral analysis of vibration.The problem is to know if the vibration is high due to the excitation itself,to a high hydraulic system is high due to the excitation resonse or to a runner/motor resonance.The vibration will be at a frequency fb given by: Fb=n*
10、f*zb= With maximum amplitude at the lowest diametrical mode excited k according to the following equation(tanaka 1990): n*zv+-k=m*zb Another typical phenomenon that can generate vibrations is cavitation.Cavitation can take several forms and can result in vibrations,losses of performance and erosion.
11、 The most common type of cavitation is part load suige. Its negative effects are usually mitigated by means of air entrapment in draft tube. On the other hand, inlet cacitation provoking erosion of runner blades is also a concern due to its destructive effects. - 3 - Here there are some examples for
12、 both types of hydraulic excitations. High vibrations in thecasingof a multistage pump A multistage pump had high vibration levels in the casing during operation. The generated vibrations produced the burst of pipes and other elements. Initially, it was thought that the vibrations were due to wear o
13、r damage(malfunctioning). As a result, the pump was completely dismantled and repaird. Surprisingly, the vibration did not disappear. A general scheme of the pump is given in fig,2.During pumping the machine delivers a flow rate of 2.8 m3/s to a head of 935 m.Other machine characteristics are listed
14、 in Table 1. To understand the cause of the high vibertion levels some experimental measurements and a theoretical analysis were carried out. From the spectral analysis it was found that the vibration amplitude occurred at 150 Hz which is fb(see Fig,5).therefore,the vibration has a fluid dynamic ori
15、gin and its high amplitude might be due to several reasons such as high RSI excitation due to design,mounting,damage,or resonance. In this case,the RSI analysis gives a pressure pulsation around the impeller with a diametrical mode k=-2 rotating in the opposite direction of the impeller st fb. First
16、 of all, the hydraulic system response of the return channel was calculated using a transfer matrix method. No frequencies around 150Hz were found. Furthermore, the analysis of the measurements(phase and amplitude variation)at different roating speeds neither showed resonance around the excitation f
17、requency. Modal analysis from the impacts done with an insteumented hammer was carried out to check the possibility of mechuanical resonance in the casing or impeller. For the casing,no resonance was found at around the frequency of 150 Hz as it can be seen in Fig,3. Atheoretical analysis with FEM gave similar results. The frequency response functions obtained from impacts in the impeller are
