Yes, another Grundfos problem

[joepfeiffer]

Hi Guys
I have a 22SQE / CU301 system installed in 07/2006. CU301 went bad in 11/2009, and again now. (By bad I mean there is no constant pressure, just cycling constantly during water use.) I can get the CU301 covered under warranty (labor not covered), but am wondering if that's just kicking the can down the road a little. Well man says he recommends the Cycle Stop Valve, but I'm wondering:
1. CSV website says that pump (when flow is restricted by the CSV) will draw fewer amps. Why? Isn't it 'hard' on the pump to be fighting the restriction of the CSV?
2. I called Grundfos and their local distributor, and both said the CU301 is not unusally problematic. Reading here, though, it IS. Does anyone know how many of these are sold each year, and are we only hearing about the problems of the few who have them?
3.Biggest concern: I have a 1.25" incoming service. Would the corresponding CSV cause me cycling problems anyway? Specifically, when small amounts are used (ice cube refill,rinse dishcloth, etc.) which happens a lot here, wouldn't the pump cycle short? I think the min flow rate is 1 gpm; we often use less.

[Possibly pertinent info: pump is at 160'; static water level is 41';]

Thanks for the help, guys.

Joe

[video=youtube;fYfxK-Pm4Fc]http://www.youtube.com/watch?v=fYfxK-Pm4Fc[/video]

 

[LLigetfa]

Have you seen this video?

http://www.cyclestopvalves.com/video/amps-csv-vs-vfd-dsl.wmv

 

[Sponsor]

 

[joepfeiffer]

Yes, this claims what I said it claims, but I'm a skeptic by nature.
As far as I understand it, the claim for the CSV energy use is that restricting the flow lowers energy (amp) draw. If this is so in theory, then in the extreme, if I restrict flow 100% (i.e. shut off all flow) amp draw should drop to zero, more or less.
Obviously not. But what is the basis for the claim of lower energy use?
And anyone know about concern #3?
Thanks!

 

[Texas Wellman]

I'm sure that Valveman will chime in here shortly but here is my answer.

The pump uses less energy when it is cut back because the amps are directly proportional to flow. The amps will never be Zero while the motor is running but the least amount of amp draw will be when there is zero flow (and max pressure) and the most amp draw will correspond when there is maximum flow.

The pump "sees" work when water is moving for a centrifugal pump. The pump "sees" no work when there is no flow, and you basically draw idle amps. Kind of hard to visualize but once you've clamped an ammeter or two on and watch it move you'll quickly understand the concept.

I don't think CSV ever claims to save energy, only that the energy will be reduced when the flow is reduced. In actually the CSV either saves no energy or actually uses a slight bit more but you'd probably never notice it in your bill.

I have always like Grundfos and their products but perhaps a VFD is not the right choice for your application? I would say that there are some areas where I would prefer VFD over CSV but if you've already had two failures I might cut my losses and try another method.

 

[joepfeiffer]

Thanks, TW. Intuitively, it seemed to me that if a certain amount of work was being done (water flowing), and then you resist it (regulator, CSV), More work needs to be done to not only move the water, but now to overcome the resistance of the CSV. I pictured it as pulling a car with a rope, and pulling a car with a rope and the brakes on. The latter would take more energy to get the same movement.
I'm going to have to think about this some more...

 

[Texas Wellman]

Of course it takes more energy to overcome the CSV, it is a restriction in the line just like a valve, 90, or any thing other than smooth open pipe. But I do not think it adds enough head loss to make a very measurable difference, probably no more than a few dollars per month. I do not think anybody will decde on CSV/VFD based on energy savings/usage (because they do not save energy).

Depending on your usage a VFD can actually consume quite a bit more energy.

 

[LLigetfa]

A rope and a car is analogous to a positive displacement pump which a jet or submesible are not and so it's a poor analogy. Are you suggesting the videos that CSV made of the ammeter are doctored?

 

[Valveman]

Sorry for the delay, I have been working too hard. Thanks Lligetfa and Wellman, you guys explained it very well. These two things about pumps are “counter intuitive”.

1. CSV website says that pump (when flow is restricted by the CSV) will draw fewer amps. Why? Isn't it 'hard' on the pump to be fighting the restriction of the CSV?

You would think slowing the RPM of a pump would reduce energy consumption. In reality it cause 5 to 6 times as much energy to be used per gallon produced.

You would also think restricting a pump with a valve would make it work harder. In reality the amps or work is reduced because it is lifting much less water. So nothing is doctored in the video. I can barely run the camera, much less get that tricky.

2. I called Grundfos and their local distributor, and both said the CU301 is not unusally problematic. Reading here, though, it IS. Does anyone know how many of these are sold each year, and are we only hearing about the problems of the few who have them?

I don’t know how many of these things are sold each year. But I heard the manufacturer loses 6 million a year on the SQE. It is a big part of their R & D. It shows everyone they are the smartest pump company in the world. So when you need a standard 5 HP or 20 HP pump, which is where they make their real money, you will think of Grundfos. Doesn’t seem that smart to me. If I got a bad taste in my mouth over the SQE, I would look for a smarter pump company for all my pumps.

3.Biggest concern: I have a 1.25" incoming service. Would the corresponding CSV cause me cycling problems anyway? Specifically, when small amounts are used (ice cube refill,rinse dishcloth, etc.) which happens a lot here, wouldn't the pump cycle short? I think the min flow rate is 1 gpm; we often use less.

The only time friction loss in a CSV is a concern, is when you are trying to use the max flow the pump can produce. Then the friction loss of the valve and everything else reduces the flow somewhat. When the CSV is restricting the flow because you are only using a small amount of water, it is adding artificial head to make the pump think it is in a deeper well, so it pumps less water. The same pump put in a deeper well, will pump less water and draw less amperage. Sounds funny but its true. Just how pumps work. Even or especially engineers have problems with this. They expect everything about pumps to be intuitive, but its not.

The CSV is nearly always one size smaller than your pipe size. The CSV is matched to the pump, not the pipe. A short 1” valve is not going to restrict the flow when using less than about 30 GPM.

You can use as large a tank with the CSV as you like. I prefer a 4.4 gallon tank, that holds 1 gallon of water. 1 gallon lets an icemaker fill or you can rinse a toothbrush without the pump starting. Even using less than 1 GPM will not cause short cycling. Drawing ½ of a GPM with a CSV will still cause the pump to run for 2 minutes and be off for two minutes. A larger tank would allow a few flushes before the pump must start. No matter the size of tank you use, the CSV allows all the water to be used from the tank before the pump starts. The SQE is always at 50 PSI, so no water every goes in or out of any size tank. The pump must start every time a faucet is cracked open the smallest bit. So you have been living with absolutely zero drawdown from the tank using the SQE.

 

[Cacher_Chick]

I don't want to steal the thread, but what I would like to see is a measurement of the force applied to the thrust bearing of a pump which has it's output restricted vs. the thrust force on a pump that has an unrestricted flow.
This seems to me like it would be a valuable measurement in determining what the potential difference there would be in pump wear.

 

[Valveman]

Good question CC. There is most certainly more pressure on the thrust bearing in a motor when the pump flow is restricted. This can be measured as the K factor. As long as the K factor at shutoff is less than the rating of the thrust bearing, there is absolutely no wear. This is because a Kingsbury type thrust bearing is completely frictionless. There is a thin film of water between the thrust pads and the plate. As long as there is enough flow (1 GPM) to keep the motor and bearing cool, the plate never actually touches the thrust pads. 1 GPM is plenty for cooling, because the amps are reduced and the motor is “de-ratedâ€. It is actually de-rated enough to safely pump hot water, so 1 GPM of cool water is more than sufficient for the motor.

There is also more radial deflection of the impeller, and more load on the radial bearings. However, this is not a problem because a submersible has a bearing or “bushing†above and below each impeller. These radial bearings are also water lubricated and cooled. A thin film of water makes an excellent bearing as well as a lubricant, as long as it stays cool. This is the reason for the 1 GPM minimum that is built into the CSV.

Large end suction centrifugal pumps are more susceptible to radial deflection. This is only a problem if the motor shaft and radial bearing are not strong enough. And I would say that if these things cannot handle a little radial deflection, you should look for a more reputable pump company.

Take a look at the picture in the following link to see a thrust bearing and impeller that was tested at very low flow for 12 years. Both still look like new. Pump and motor companies have had to quit saying the CSV will damage bearings, because in over 18 years it has never happened.

http://www.cyclestopvalves.com/csvtechinfo_4.html

 

[joepfeiffer]

Thanks, Everyone for the imput. I was shut out of the forum today ( site down?) and couldn't monitor responses as timely as I wanted to.
I think I'm 'kind of' getting it as far as the energy use issue, and looking at their own figures with a fresh eye, I'm not too enthused about the SQE. But I'm still thinking about the following:
Suppose I turn my SQE into an SQ (it's already that - he was out here today and replaced everything [cu301, sensor, pressure tank] but the pump - still cycles 60-80psi every 10 seconds, diagnosis: must be the 'chip' on the pump). Ice cube tray trips the pump on. Only water draw needed is to fill the pressure tank. at 1gpm, takes about 1min. Pump on for 1 minute to fill ice cube tray? Main question - will this low flow - 1gpm for 1 min - be enough to cool the pump (10,000+ rpm) or not?

 

[Valveman]

If you have the 2.2 gallon tank (<1/2 gallon draw), it should only be taking a couple of seconds to fill from 60 to 80 PSI. It can't be pumping for 1 minute unless water is going somewhere. But yes 1 GPM is enough to cool that pump, even at 10,000+ RPM.

 

[joepfeiffer]

So, I should make sure to have at least a 1 gal drawdown in my pressure tank, so as to keep the pump on for a minimum of 1 min?

 

[Valveman]

Sort of. The gallon of storage is more for filling the icemaker or wetting a toothbrush. Most other times water will be used for more than 30 seconds, the CSV makes the pump run for as long as you are using water, so you really only need about 30 seconds of tank fill time. But you don't get any run time or drawdown with any size tank when using a VFD.