Goulds constant press & variable speed pumps

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Bob from Plains

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Do any of you out there have any advise on the Goulds ITT variable speed constant pressure submersiable pumps and associated equiptment that goes along with it. How is their track record for maintance and do they do what they say they can?
Bob
 

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Variable speed pumps are not a new thing. However, many of the band aids they come up with to try and solve some of the inherent problems of VFD are new. Flow through tanks help keep the water in the tank from stagnating. Switches instead of transducers help the reaction speed of the VFD to reduce some of the water hammer and pressure surges. Harmonic filters help keep the VFD from sending dirty power back into the electric grid. Computers installed inside the motor instead of above ground, allow the water to help keep the electronics cool without the need for a fan in the control box. This helps keep out lint, bugs, and heat, which are the worst enemies of a VFD that is hanging on the wall of a well house. Some of the new larger VFD's now have a "sleep mode" which allows a pressure bandwidth so a pressure tank can actually accept and express some water. VFD's are getting smaller, lighter, cheaper, and may even be lasting a little longer.

All of these things are just band aids. Unless you can change the laws of nature, there are many things about the VFD that can never be fixed. Higher RPM's of a VFD pump can cause premature wear. VFD pumps and motors vibrate at certain speeds from a resonance frequency that can only be skipped not fixed. Reflective waves and pulsing DC voltages cause the motor to receive much higher voltage than it was sent, depending on the length of the wire. This higher voltage can cause premature failure of the windings in the motor. The list of side effects from using a VFD can go on and on.

The function of a VFD is so complicated and the side effects are hidden by so much smoke and mirrors, that it does not surprise me that even someone with Speedbumps experience in the pump industry, has not heard of these things. Many of the people who sell VFD systems either don't know or don't want you to know all of the ins and outs of this type system. The long list of negative side effects are never mentioned, as all they want you to hear is "constant pressure" and "energy savings".

Restricting the flow of a normal pump with a simple valve can reduce power consumption the same as a VFD. Therefore, claims that a VFD can save energy, are simply not true in these type applications. The CSV mimics the "constant pressure" and "variable flow" of a VFD. However, the CSV gives you these benefits without any of the negative side effects that are inherent with VFD controls.

Here are some more links on the subject;

http://www.cyclestopvalves.com/comparisons.html
 
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