RE: Pump Noise

["Jeffery Ludwig" <jjl22 at drexel_edu>]

> I have always wondered why rotary water pumps can go from 
> totally silent to 
> quite noisy.  I have tried measuring both the magnetic rotating drive 
> "thingy" and the "hole" in the coil.  Nothing definite there. 
>  I now wonder 
> if somehow the "shorting" coil in the potted drive 
> electromagnet, develops 
> more "shorts" and thus messes up the "rotating magnetic 
> field."  Regardless, 
> they get pretty noisy after a few years.  I also notice that 
> the really noisy 
> ones generally don't automatically start spinning the drive 
> cylinder, but 
> have to be "flipped" to start spinning.

A little OT but for those with sumps...

I assume most aquaculture pump manufacturers have built their pumps
conservative, but for efficient centrifugal pump operation it is key
that you meet the Net Positive Suction Head available (NPSHa)
requirements of the pump.  A noisey centrifugal pump usually indicates
there is significant cavitation (vaporization of fluid) in the impeller
chamber.  A simple way to keep enough back presure on the pump to meet
requirements is to keep the liquid level well above the pump intake.
Granted this usually occurs in industrial pumps with a fluid that has a
significant vapor pressure, try raising the liquid level in your sump to
quiet it down.

Cheers,
Jeff Ludwig
Philadelphia PA