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Vertical Pump - Modal Analysis

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If I'm not mistaken, Vibrant Technologies has a version of MeScope that allows the user to input variables (e.g. mass of water) and make assessments of what you are looking for. You might want to contact them directly. For the modal test, are you impacting above ground and obtaining response data from the support column below ground? I've not done that but would be very curious how well the data comes out. So when the ODS is performed (now there is the added mass of the water in the wetted piping) you are hoping you might see a change in Fn. You're right in that you may or may not even excite or see the mode(s) depending on location of Fn to running speed. You could try to "jog" the pump to provide an impulse to the whole structure in the hopes it might provide enough energy to see the modes. If you do find solution to this testing, please share. Best regards, Jim Powers

Hi Jim, Thanks for looking at this and replying. I will most certainly look into the mass of water/ME' Scope issue. I am curious about this as well. The guy we've hired to do this testing is one of the best at Modal/ODS that I know of and has years and years of experience so I am the results we will get are as accurate as possible. Like you said, we will be using a combination of coast down testing, ODS, and Modal data to try to narrow down where those frequencies are and how much they shift with and without water. I will look into the ME'Scope possibility and get back to you. Will also share the amount we find the NF's shift with and without water. Thanks again for your help. KB

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I have done this type of testing on large vertical pumps, but not with ME-Scope. Water inside and outside the pump column adds mass. A rule-of-thumb is to use twice the volume of water inside with same sump level to account for the mass of water outside the column. There can also be a difference in natural frequencies with the impeller support conditions between wet and dry. Pray that the stop logs hold back the water when you are standing knee deep in water, muscles, and gunk while impacting the pump inlet bell! Walt

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