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OLi

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Reply with quote  #1 
Have you seen a direct drive 2 bearing fan OH where H reading is low 3-4 mm/s and V at one end of the bearing is 4mm/s and the other end 50-70 mm away is 12mm/s at reduced speed and 20mm/s at desired speed and the other bearing is the same but mirrored in axial respect. Balancing gave readings fluctuating 100 DEG so they didn't really try. It seems that the support differ at those points so I told them to look at that last evening possibly prop up by a 2"x4" to see if it changed so they could run as desired and I have not heard anything more so it may be the case. It was a phone distance support but it was a funny variation I can't say I have seen before so I thought I would share it. Fans do have all kind of features. It gave the user a quick intro in "in head" brute ODS thinking by measuring a few points around those previously measured anyway. It sure may be more complicated but it was one of the simple things possible to test during operation. Olov  
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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Danny Harvey

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Reply with quote  #2 
Oli,

In a typical middle sized fan manufactured in the eastern US, they use an A-frame pedestal to hold the bearings in an overhung configuration.

I have seen quite a few instances where maintenance has perceived vibration under the fan side bearing and, being unable to balance, welded the plate to the horizontal stiffeners. In almost every case, it has resulted in increased amplitude at 3 x running speed. Removing the weld and balancing the fan has corrected things.

I think it was Rick Little who identified this issue to me. Whoever it was, it was right on the money and I thank him.

I should add that my case referred to v-belt driven fans.
OLi

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Reply with quote  #3 
That was also a special one with 3xRPM, my case supposedly have at least 70-80% 1xRPM and made in south Sweden but I have not seen any data yet. It is only a year old and the fan center plate had cracks and fan wheel was replaced. A test was now performed with jacking vertically and improved a lot. I did tell them that if hydraulic jack was used it is in fact a hydraulic damper they apply and that is a bit different.... at least compared with a 2"x4" pine. They stop Tuesday so we will see. Olov
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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Dan Timberlake

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Reply with quote  #4 
Hi Oli,  got any pictures of the actual installation, or a very representative one?

regards,

Dan T
OLi

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Reply with quote  #5 
Something like this. I thought I had seen it but it was another they also had problems with. Olov

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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se

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