CSV vs. VFD

VFDs are pretty reliable, but they might not be as precise in maintaining constant pump discharge pressure as a downstream pressure regulating valve could be. Which of these is this valve company actually talking about?

What percentage of the rated motor capacity is the system presently using and how much can you cut things down before low flow/pressure problems arise?

Then from that what is the calculated return on investment for energy/operatinal costs saved Vs the purchase and installation prices of each system?

That's the data that will tell you which will work best.

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http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1011&context=archengdiss

I don't know much about heat pumps, but the title "cycle stop valve" seems at odds with maintaining a constant outlet pressure.

Also it sounds like there is something else in the circuit to reduce the flow. Presumably the CSV throttles to maintain pressure downstream of the CSV. Depending on the pump curve that might reduce power a tad (or it might increase it), but unlikely to be significant.

I order for any pressure regulating valve to work the pressure on the upstream side must be higher or equal to than the set pressure.The name of the valve suggests that the system pumps up to above set pressure then stops the pump until the upstream pressure decays to just above the set pressure before restarting the pump. I presume that the over pressure range can be adjusted but a 25HP motor draws a lot of current on start up, which heats the windings and limits the number of starts per hour. Given that the pump is currently running 24/7 it suggests that the pressure decays rapidly so the over pressure setting will be high to limit the number of starts per hour. A pump running at full throttle to generate a higher pressure in stop start mode always consumes more power than a pump running at lower speed using a VFD. A consistently high number of starts will reduce the motor life. The VFD will auto correct but the actual energy saving will depend on how much the pump has been over sized. VFD regulation will not be as precise (lag on the feedback will be longer) but that is the penalty you pay for a reduction in power usage. In your application the difference in precision may not be noticeable.

I just did a quick calculation on running a 25HP pump 24/7/52 and it came out at £28,000pa using typical UK industrial electricity prices. So I looked back at the post and realized that it is the whole system running at 25HP so the pump is probably only ½HP. Look at the power factor of the pump. You might make more savings by just adding power factor correction capacitors.

I've followed the csv vs vfd debate for some time. My motive is that I have three domestic wells. I retrofitted two of them with vfds in 2011 and 2014. So if mtbf is 10y, my first vfd failure is due in 2021. It could well run well beyond that.

I worked in power plants for almost 40y. Every day, I watched centrifugal pumps in many applications. I know that minimum load (amps) is deadhead. That is why a centrifugal pump should always be started with the discharge valve closed or cracked. I've seen the consequences of doing otherwise. I also saw pump amps vary with load. So that shouldn't be a matter of debate.

I paid $500 on Ebay for my first NEMA 4 Monodrive XT. I paid $1000 for my second, NEMA 1 XT. I like what they do. I don't have to size sprinkler zones now. Golf courses use VFDs for the same reason.

I recently bought my neigbor's place. It had a well with a pump that I suspected was beyond its life cycle. So I thought a lot about refitting it. This is what drew me to the csv vs vfd discussion. I worked with vfds from 1 hp to 8000 hp, so I understood the application, and liked it. The best, I thought, was when we replaced coal feeder clutches with vfd motors. Truly amazing.

I am also a businessman, so I cringed at the thought of refitting this new well with a 1.5 hp pump and motor, and a Monodrive XT. I do all of my maintenance, so my cost was about $3000 for a pump and motor, XT, flex hose and new cable. The area pump people would have charged as much as $5000. This is what motivated me to look for an alternate constant pressure solution.

As I said, I worked in power plants. I understand centrifugal pump amps and minimum flow requirements. I also understand pressure control valves that are described in these forums as "cycle stop valves." One fundamental difference is that the CSVs are made so that they don't completely close. That meets the minimum flow requirement. And that they begin to restrict when the set pressure is achieved meets the constant pressure requirement. And the < $100 price of the CSV is certainly beats the current $1300 price of a Monodrive XT.

That leaves economics. My CSV throttles mainly when my tenant uses domestic water. When pressure falls to the lower pressure switch setting, the pump starts. Pressure rises quickly to the 40 psi CSV setting, and begins to throttle. That the CSV does not close completely causes the pump to run long enough to prevent the effects of short cycling. When my irrigation cycle starts, the pump starts. The CSV prevents the pump from stopping for the entire 1.5 hour irrigation cycle. And pressure is 40 psi max, unless a zone causes perssure to fall below 40 psig. So the CSV appears to be functioning as I need it to. And the cost savings was $1300-$100. One would have to save much more than that in power over a 10-year pump life cycle to justify a VFD. Based on my experience and understanding of centrifugal pumps. there may be NO power savings.

Finally, I installed my first pump in 1978, when I built my home. I maintain a log on my three wells. Pump life cycle is as long as 15 years. In the summer, two pumps run 2 hours daily each, and the new one runs 1.5 hours. All three are connected to domestic water systems, so they also cycle for that reason. All three pumps are Franklin pumps with 1.5 hp single phase motors. All three are set at about 100 feet. Static water level is 65 feet. As I said, the two older pumps have Monodrive XT controls. The new one has a 40 psi CSV. It is in its second irrrigation season. I paralleled an LED lamp on a 100' extension cord to the fence between the rental and my house so that I can see when the pump cycles.

I think my three wells are near-ideal laboratory settings for this CSV vs VFD debate. I'm willing to share my experience with the CSV as it unfolds. I will consider it a profound success if the pump, motor and CSV life cycle is 10 years. And if one does a disciplined financial analysis, it doesn't have to be that long. With a VFD, commercial cycle cost is $4k-$5k, or $500 annually. My cost is $2k. With a CSV, my cost is $1100, or $110.

I want the facts in this matter. I've heard some real experience with CSVS, and a lot of pontificating about VFDs. I'd like to hear more real-life experience with both. Looking forward to hearing about them.

I started working with pumps over 50 years ago, and with VFD's over 30 years ago, which led me to Cycle Stop Valves in 1993. Having been doing this for so long I know what your outcome will be. But I am happy for the comparison. I have been looking for the con's to Cycle Stop Valves all these years and have yet to find one. It took several years for me to find out the major pump companies couldn't find any flaws either. About 1998 I finally found out the major pump companies had blacklisted the CSV. They told all their employees they had tested the CSV. "The CSV makes pumps last longer and use smaller tanks. This company makes pumps and tanks. So, any employee who mentions a Cycle Stop Valve will be fired immediately."

After hearing something similar from about the third major pump company I realized there are no flaws with the CSV. The reason pump companies do not promote the CSV is BECAUSE it makes pumps last longer, and they don't like that. I have learned the hard way that too many things in industry are controlled by the marketing people and their planned obsolescence. The best engineering and what is best for the end user gets pushed completely out of the market in favor of repeat sales. Doing what the big companies are spending the most marketing like VFD's keeps the cash flowing to the corporate offices. Doing your own research and figuring out how these big companies are duping the people is the best way to make your water system last longer and be more efficient.

first queston.. what type of pump you using? Centrifugal or a another? Second, what type of motor? Single phase or 3 phase!

VFD or variable frequency drive, controls the output Hz, which in turn controls the RPM of the motor/pump and using the laws of affinity, the flow rate and head.

The type of pump will dictate the type of control you use. While a VFD is one method and it can be used in a closed loop control to deliver a constant flow, it might not be suitable for this application as most motors will stop at 40Hz and lower, and if the control lowers the Hz to that or less you might find your pump has stopped.