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1

Frequently Asked Questions / Re: Still reading ...

« on: August 15, 2018, 08:17:03 AM »

Cavitation happens when you restrict the suction of a pump, which we do not.

I specifically said "Discharge Cavitation".  I pasted a link and pasted text from the link that specifically addresses discharge cavitation.  At no time did I say anything about restricting the suction.

Restricting the discharge of a pump can cause re-circulation within the pump, but as long as the water doesn't heat up from re-circulating, it doesn't cause any damage.

That's not true.  Restricting the discharge of a pump can cause cavitation as explained in the link I included in the post to which you are responding.  Last night I spoke with a mechanical engineer who specs pumps and knows more about this subject than you and I can ever hope to know. He agrees with me.  Unless you design the bypass according to the pump curve of a specific pump, you can get discharge cavitation.  The bypass you have designed might be right for some pumps and wrong for others.

I read some reviews.  I don't care about reviews.  Reviews are from people who may not understand how this stuff works or may not have run the product long enough to know whether the product is causing damage.  The more I learn about CSV's (which is really just a pressure control valve, not some curious new invention), the less I trust that it will not damage my pump.   I don't need to read reviews because I have no doubt that a pressure control valve works great, when spec'd properly against my pump curve.  It's even possible that your pressure control valves will work great with my pump.  But you have not convinced me that your pressure control valves will not damage my pump because you don't know what kind of pump I have nor do you know what the pump curve looks like for my pump (and neither do I, actually).

If pump manufacturers could find a more profitable way to control pumps, then they would do so because it would give them a competitive advantage over their competition.  I don't believe they are all conspiring against you.

My VFD has not eaten any pumps in 8 years in stark contrast to your claims.

Thank you for trying to address my concerns.  I will stick with my VFD.

2

Frequently Asked Questions / Re: Still reading ...

« on: August 13, 2018, 03:57:16 PM »

The conspiracy theory stuff doesn't particularly interest me, just the technical.

As such, I guess I don't understand your statement:

A CSV can never close completely, therefore it can never deadhead the pump or cause cavitation.

...when there are lots of sites that describe discharge cavitation when operating against a restriction at rates far below BEP, for example:

https: //blog.craneengineering.net/what-is-pump-cavitation   (I can't post links so I've added a space in the preceding link to fool the parser).

When a pump's discharge pressure is extremely high, or runs at less than 10% of its best efficiency point (BEP), discharge cavitation occurs. The high discharge pressure makes it difficult for the fluid to flow out of the pump, so it circulates inside the pump. Liquid flows between the impeller and the housing at very high velocity, causing a vacuum at the housing wall and the formation of bubbles.

So are you saying that the CSV's are calibrated for each particular well and pump to ensure the pump does not run far enough below BEP so as to cause cavitation?  It would seem that would be something more important to put on your site than the many conspiracy articles.

3

Frequently Asked Questions / Still reading ... from a VFD owner

« on: August 12, 2018, 08:50:43 AM »

First, let me provide a bit of background.  We bought our place about 8 years ago with a 60/40psi 60gal pressure tank and a Franklin Electric pump controller (capacitors and contacts).  I didn't like how water pressure varied and we were renovating the entire house while living in it on weekends. So I went into the Pump store and they sold me on a Monodrive to run the pump (that had been down-hole for, my estimate, 25 years).  I was happy to get rid of the big 60gal tank and reduce my pumping footprint to a small amount of wall-space.  I'm not an engineer but I play one on weekends and a VFD made intuitive sense to me.  For 4 years we ran the pump that way and it was awesome.  I even ran an A/C coil in my furnace plenum but pumped well water through it because the water comes out of the ground at 6degC in these parts.  The coil was a 1/4" ID so flow rate was small but the VFD ran it fine.  Some months, the thing ran continuously because we have a lot of south facing windows and the place heats up real good.  The well is 10gpm and I was monitoring the head by tracking current draw on the pump (the higher the current draw, the lower the head, I wanted to see whether I was drawing the well down close to the pump.  Turns out I wasn't, even with irrigation and regular household use).  Suddenly after about 4 years, the well failed.  The drive started pumping black silt and the Monodrive kept shutting down the pump because it was plugged.  The well guy came out and it turns out he's the same guy who drilled the well 35 years ago and as far as he knew, that was the original pump that was in there.  Turns out the steel casing collapsed into the well and he tried to retrieve the pump but after a few hours, it was clear it wasn't coming out.  So we abandoned that well and drilled a new one about 50' away.  He dropped in a new 3/4" hp pump and hooked it up to the Monodrive.  He's not a VFD fan but wasn't able to explain why; just that he'd seen controller problems in the field.

That was about 4 years ago.  2 years ago we ditched the hillbilly swamp cooler and bought a real A/C unit but are doing a lot more spray irrigation now.  The new pump has run flawlessly for 4 years of regular use with some irrigation. 

Last night we had a terrific light show outside.  A couple hours of lightning and cracking thunder.  Then at 9:00PM I noticed we had no water.  I checked the Monodrive and it was reporting an under-voltage condition.  I buzzed out the line and it was a nice solid 240VAC.  I checked the cooling fan and it ran nicely at 9v. I cycled the Monodrive a few times and it kept reporting the same condition. I threw my oscilloscope on the incoming power and it looked clean.  I decided to start googling and came upon this site.  While reading the site, I heard the shower turn on as my teenager decided to have a "shower" (yeah, yeah)... I looked at the Monodrive and it was all happy as though nothing happened.  I concluded that something was going on down the line from the lightning storm giving us crappy power that I wasn't able to see on my scope.

I do embedded firmware for a living so my day job has me closer to being an electrical engineer than anything else, but in my hobby time, I tend towards the mechanical.

Now this morning, I'm digesting the contents of this site and I'm somewhat skeptical as I am with all new things.  I'll buy into something if it makes intuitive sense.  I immediately understand how a centrifugal pump uses less energy with greater back-presssure, that's just intuitive to me.  Unfortunately, from what I know about centrifugal pumps, when there's excessive back pressure, running outside of BEP, they begin to cavitate.  I know that cavitation is what will prematurely destroy a centrifugal pump and that's also intuitive to me.  So it would seem that a CSV would cause a pump to cavitate which is not what you want.  That's the biggest thing I can't resolve in my mind.

Around here, electricity is fairly cheap so I'm not super concerned about saving electricity.  I just want to have a nice shower and that's the biggest reason I have a constant pressure setup.  I've got to be honest, reading the content of this site, the wording is very "snake oil" even though I completely understand the principal behind the CSV and it makes perfect sense.  But when I start reading articles with lots of unbacked assertions and possible falsehoods, I lose interest and increase my skepticism.  Because of this verbiage, I'm not inclined towards replacing my VFD with a CSV.  It seems like the site is trying too hard to sell something that should be self-evident if it was truly better.

Examples (new account, I'm not allowed to post links):

1) The power-consumption-cycle-stop-valve-vs-large-hydro-tank page is doing payback calculations on 1200GPM pumps.  I'm thinking the average acreage owner doesn't have a 1200GPM well and I'm not convinced this stuff scales down linearly to 10GPM.  Based on current measurements I've taken from my system while it's running, there is definitely less power consumption when the pump is spinning slower (though it's tough to correlate because I don't know what's happening with the water level inside the casing).

2) One of Cary's posts in the forum, he asserts "The only restriction that will hurt a pump is one that make the water heat up." and I don't think that's true for a centrifugal pump, as above.  A restriction causes cavitation which will hurt a pump.   Overheating should be the least of your concerns with a submerged pump in the bottom of a hole full of 6degC water that is constantly moving while the motor is spinning.

3) The internal memo from Grundfos makes a lot of sense.  I don't see it as a 'sales tactic' and in fact raises some good points that are not adequately (in my mind) refuted in the response posted above the letter. In fact, in the response is the sentence "Many studies have also proven that VFD's do not save energy and shortens the life of pumps and motors" but in fact, there is only one 'study' in the links that attempts to explain this but it is a power point slide that is missing the corresponding speech that would expand on the points.  The rest of the links are all expired (404).  So the response reads (to me) like FUD.   If there are 'lots of studies', they should be easy to find and the links shouldn't disappear.

4) The "Letters from Pump & Motor Manufacturers" page section attributes the same letter (Kevin Price of Sun-Star Electric, Inc) to two different sources.  (Hitachi and Centri-Pro Sub Motors as well).  That might have been an oversight.

5) The page "csv-vs-vfd-power-factor-and-kw" appears to show that a VFD actually does use less energy than a pump controlled by a CSV.  Again, I don't care about energy savings but it does suggest there is some truth to the VFD manufacturers claims in direct conflict to the unbacked response to the Grundfos letter.

Again, I'm not inherently skewed towards VFD and I only have one horse in this race.  I do agree that sometimes simpler is better; in fact I own a 1972 Toyota as well as a 2015 Ford.  The '72 Toyota is way easier to fix than the 2015 Ford and is several orders of magnitude simpler.  Unfortunately, the '72 is a hobby vehicle because, in just about every way, the 2015 Ford is superior and day to day, I prefer to drive the Ford. 

The two biggest things I can't resolve in my mind are:

1) Pump cavitation.  How is this not a problem when controlling a pump with a CSV?

2) The CSV site says over and over that I will be replacing my pump every 2-3 years.  In stark contrast to this, I have now run 2 pumps for 4 years with no problems that can be attributed to the VFD.  In fact, the first pump was at least 25 years and possibly 35 years old, and it ran fine for an additional 4 years on a VFD so I have trouble believing that a VFD is hard on a pump.  The previous owners of this home warned us the pump was likely in need of replacement as they had never had it replaced since they had the well drilled.  I'm willing to concede that they may be mis-remembering but at least it was probably 25 years old.  In fact, the VFD might have saved that pump because it detected a problem and shut down the pump.  We'll never know since it's now at the bottom of the old well.


On to the financial... I paid $1100CAD for my Monodrive setup which included the controller, manifold, pressure switch and 1gal pressure tank.  If the controller itself fails, maybe it costs $800CAD to replace.  Just an estimate.

To replace the Monodrive with a CSV setup including a monitor is about $255+$365 so about $600USD plus shipping, so about the same as replacing my Monodrive when it fails.

Since I haven't seen any empirical evidence that pump life is shortened by the VFD, the buy proposition is simplicity.

But I can still be convinced.