The guy that invented the CSV goes by valveman on several different sites. Here is one where he talks about the thrust bearings and impeller wear.
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www.terrylove.com/forums ··· e-ValvesHere is a post on valveman's site where they talk about the increased pipe pressures. Basically it's not as bad as you would think. (FYI my well pipe is stamped 450 psi)
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cyclestopvalves.com/smf/ ··· c=1897.0In this thread a plumber gives his endorsement to the CSV and why he doesn't like VFD's.
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www.ridgidforum.com/foru ··· /t31330/In this thread some engineer types talk CSV vs VFD.
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www.eng-tips.com/viewthr ··· d=254975Here some electricians talk about the life expectancy of VFD pumps.
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forums.mikeholt.com/show ··· t=130792I could go on, but I did a lot of research on the subject. It's safe to say that there are a lot of very knowledgeable people out there who believe VFD pumps aren't that great. There are also a lot of professionals out there installing CSVs over VFDs. In the end there are several topics in play here.
Upfront cost: The VFD is undisputed as costing more
Pumping cost: The electrical usage of a 10gpm VFD and 10gpm CSV pumping @ 5gpm are very similar
Pump cycling: The VFD and CSV both reduce pump cycling a similar amount if you size the pressure tanks correctly.
Long term cost: The VFD would have to last longer than a standard submersible pump with a CSV to come out on top, and yet I find lots of people stating the VFD doesn't last as long, and basically nobody stating the VFD lasts longer.