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askjoet
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Join Date: Aug 2006
Posts: 99
Good Answers: 1

Harmonic Dissonance and Vibration

04/24/2007 2:06 PM

I need to evaluate vibration in a water fluid system when pump speed is increased via a VFD through a test cell pressure drop. I suspect dissonance but it has been quite a while since I chased that particular gremlin. The vibration is at the pressure drop device in a 1" pipe. No problem at slower speeds/ velocities. I can probably solve with pipe change but want to be sure what I am dealing with. Comments?

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Howetwo
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Join Date: Jun 2005
Posts: 394
Good Answers: 1
#1

Re: Harmonic Dissonance and Vibration

04/25/2007 10:53 AM

I cannot visualize your system, but cavitation will occur with resultant vibration if the NPSH for the pump is exceeded (you're pulling too much suction for the temperature of the water being pumped).

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techno
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Canada - Member - Our strength is our diversity

Join Date: Jan 2007
Location: Canada
Posts: 1024
Good Answers: 40
#2

Re: Harmonic Dissonance and Vibration

04/25/2007 2:40 PM

The only possibilities that comes to mind is:

Air has become trapped in the pressure drop device, and the increased pressure (due to higher speed) is causing a hammering effect in the device. The hammering effect would coincide with the vanes on the pump. A fix is to have the pressure drop device under the pipe, or if it has a bleed screw- bleed it.

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