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Danny Harvey

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Reply with quote  #1 
I have been asked to do vibration analysis on four of this type of pump:

http://www.pemopumps.com/pompe/pompe-orizzontali/

They all have a fairly high amplitude at 4 x pump speed (which I believe is vane passing frequency) but don't really show the broad band energy that would indicate cavitation.

Can anyone confirm that this type of pump has an inherently high vpf?
fburgos

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Reply with quote  #2 
I remember a case where bpf was so high it didn't had broadband at high frequency but impellers where destroyed in short time, the cause was an oversized pump or low inlet flow
Curran919

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Reply with quote  #3 
You can have high BPF and low cavitation if you have a high NPSHa.
Danny Harvey

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Reply with quote  #4 
Ferdy,

That's what I'm concerned about.  I don't have the exact particulars about these but I believe them to be the open impeller type that is shown in the lower right photo on the Pumps Presentation page.

This is a belt wash pump in a granite quarry.  I'm not sure of the exact make-up of the material pumped but I know it is water with some granite so it is abrasive.  I'm assuming that the reason for the open impeller is to keep rocks from getting stuck. I know that the casing is some sort of abrasion resistant alloy which is brittle as shown by the cracked housing they have experienced in one pump. (That is the pump with the highest VPF.)

To me this suggests maybe fines build-up on the impeller/housing leading to jamming of particles that are considered normal for a clean pump.

Curran,

I don't know anything about the pump selection, but as a rock quarry, these are not the most pump-savvy folks.  They really know their conveyors, Cats, etc., but there's just not that much call for pumps in the rock-pounding business.

I'll ask them to review the selection process to see what the NPSHa is.

Thanks for the tips guys.

Edit:  Now I'm wondering if perhaps particle size may have been a determining factor in selection of the pump which lead to excess NPSHa.


I'll try to get some answers to these questions.

Walt Strong

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Reply with quote  #5 
I have worked on a lime slurry pump that was part of a flue gas scrubber system. The pump had a rubber lining that would occasionally tear, and vane pass frequency would be excited. The machine was outdoors at grade level sitting on a concrete foundation. The belt-drive motor was supported above the pump on threaded rods to adjust belt tension. High motor vibrations occurred a few times after plant personnel changed belts. The entire machine was rocking on the foundation. I adjusted belt tension and vibrations diminished significantly. Structural natural frequency with nearby forcing frequency can occasionally cause goofy vibrations.

The website picture of the Pemopump installed with suction very close to a header pipe looks like a good candidate for high pulsation from poor inlet flow.

Walt
Danny Harvey

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Reply with quote  #6 
Walt,

This has the same threaded rod adjustment.  It's really easy to overtighten, even to the point of deflecting the shaft.

This is the same thing you are describing except that this one does not have the rubber liner.  They have others that do, but not these.

This actually seems like a very good installation. It was set on the anchors with the pipes aligned and then grouted. Running speed is real low. VPF is about 4-5 x higher on all pumps.
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