Paging mas985 (or anyone else who can help with pump question)

[sktn77a]

OK, so I am about to upgrade my pump to a 2 speed - probably a Pentair Whisperflo. I have estimated my total head to be approximately 40-50 feet. Looking at the head curves for this product, a 1hp pump (1.5 SF) at a head of 50 ft would produce a flow rate of 75 GPM at high speed and at low speed, the flow rate falls to zero by about 20 ft of head (implying that low speed won't pump anything at all). I know this is incorrect, but how on earth are these pump performance curves of any use to anyone and how do you determine whether a given HP/RPM will work in your pool???

Thanks in advance,

 

[jblizzle]

The head changes with pump speed. Just match high speed flow rate at a given head with your existing pump at the same head. Or have it higher or lower if you want to change from what you have.

 

[JamesW]

Half speed should result in roughly half the flow rate and 1/4 the head loss. Power is about 1/8th.

So, if high speed is 75 gpm and 50 feet of head, low speed should be about 37.5 gpm and 12.5 feet of head.

 

[mas985]

OK, so I am about to upgrade my pump to a 2 speed - probably a Pentair Whisperflo. I have estimated my total head to be approximately 40-50 feet. Looking at the head curves for this product, a 1hp pump (1.5 SF) at a head of 50 ft would produce a flow rate of 75 GPM at high speed and at low speed, the flow rate falls to zero by about 20 ft of head (implying that low speed won't pump anything at all). I know this is incorrect, but how on earth are these pump performance curves of any use to anyone and how do you determine whether a given HP/RPM will work in your pool???

Thanks in advance,

Why do you care about any of that?

 

[sktn77a]

Why do you care about any of that?

Well, because I'm trying to use the data the pump manufacturers provide to correctly size the pump. According to the pump curves, the pump delivers 0 GPM on low speed at any head greater than 20 ft. I realize that's not correct but how else do you estimate anything from these curves. Also, if they don't provide any useful information at low speed, how can I rely on the data at high speed?

 

[sktn77a]

Half speed should result in roughly half the flow rate and 1/4 the head loss. Power is about 1/8th.

So, if high speed is 75 gpm and 50 feet of head, low speed should be about 37.5 gpm and 12.5 feet of head.

Thanks James. I agree with your estimates, based on the affinity law and the flow vs head relationship as a power (squared) function. But I'm still intrigued as to what the manufacturers' curves tell us. As I responded to Mark, if you can't easily use the low speed curves, how useful are the high speed curves?

 

[mas985]

Unless you are running a spa, flow rate really doesn't matter much. Just go with the smallest pump possible to save the most in energy costs.

But to answer your question, head loss changes with flow rate so at low speed, the flow rate is 1/2 as much as high speed and head loss is 1/4th of high speed. But that really doesn't help you much because I am pretty sure your head loss estimate is not all that accurate to begin with since that depends on not only the plumbing but the pump you put on the plumbing. That's why it is pretty much pointless to go down this road unless you really really need to know flow rate.

But if you really want to know flow rate, download the spreadsheet in my signature. You can use to determine the current plumbing curve with the current pump and then determine flow rates with other pumps as well.

 

[JamesW]

If you want to estimate the flow for various pumps on your system, you have to generate a "system curve" to plot on the same graph as the pump curves.

A system curve plots the pressure vs flow for different flow rates.

A system curve starts at 0,0 and rises exponentially by about a square factor.

The best way to generate a system curve is to put various flow rates on the system and measure the suction and pressure head by pressure gauges.

The points where the system curve crosses the pump curves are the operating points.

You can estimate the system curve from a measure of total head and gpm assuming a square factor for head vs flow.

For example if you measure total head at 64 feet and flow at 64 gpm, you could estimate the system curve as follows:

Ft. Head...........Flow
64.......................64
16.......................32
4.......................16
1.........................8.

Plot that against the pump curves to find the places where the system curve intersects the pump curves.

Maybe consider getting a variable speed pump so that you can adjust the flow as needed.

In most cases, you can operate at very low flow rates for power savings and noise reduction.

 

[sktn77a]

Well, I've read all of the materials on this, I understand Bernoulli's and Poiseuille's laws from my college physics but I'm b_ggered if I can get this!

In any event, I think I've spent enough of my and your all's time on this, so I'm just going to get a 1HP Pentair WFDS4 2 speed pump and be done with it!

 

[mas985]

That is a very LARGE high head pump. You really don't need all that power and is really too much for 1 1/2" plumbing. A WFDS3 or even a 1 HP two speed SuperFlo is a much better option.

 

[JamesW]

I would suggest the SuperFlo VS.

Check for a rebate from Pentair and your local utility or government.

The cost of the VS is not much more than a 2 speed.

If there are rebates available, the choice is easy.

 

[sktn77a]

That is a very LARGE high head pump. You really don't need all that power and is really too much for 1 1/2" plumbing. A WFDS3 or even a 1 HP two speed SuperFlo is a much better option.

Well, my existing pump is a 1 HP 1.65SF DuraGlass (same specs as the WFDS4) and seems to have worked OK for the last 20 years, so I figured a 2 speed running on low low most of the time would work (I can use the high speed for cleaning/vacuuming, backwashing)?

 

[JamesW]

For high speed, I would suggest a total hp of about 1.0 to 1.25.

In my opinion, 1.65 is overpowered for your pool and system.

 

[mas985]

Well, my existing pump is a 1 HP 1.65SF DuraGlass (same specs as the WFDS4) and seems to have worked OK for the last 20 years, so I figured a 2 speed running on low low most of the time would work (I can use the high speed for cleaning/vacuuming, backwashing)?

You have to be careful when sizing a pump by label HP. It isn't that it would work poorly, just less efficiently.

For example, on typical 1 1/2" your pump would produce 62 GPM and consume 1.7kw while the WFDS4 would produce 63 GPM and consume 1.8kw. In other words, to get 1 more GPM, the WhisperFlo uses an extra 100 watts to do it.

However, the SuperFlo 1 HP, which is an up rated pump, would produce 56 GPM @ 1.4kw. A much better choice.

[Corrected for full rate and wrong data]

 

[sktn77a]

OK, I don't have those specs on the pumps so I'm trying to figure out the differences between them. From what I can gather, the difference between the 1HP up-rated Superflo (30042) and the 3/4HP full-rated and 1HP up-rated Whisperflo variants (012430 and 012485) is the 1.5" plumbing port size on the Superflow and 2" on the Whisperflo. Is that it? The prices are all over the place (even at the same dealers) so you can't go by price. Also, I see the single speed Superflo pumps have a Standard and High Efficiency versions while the dual speed and Whisperflo pumps do not. Are all the sual speed Superflo and all Whisperflo the high speed variants?

 

[mas985]

OK, I don't have those specs on the pumps so I'm trying to figure out the differences between them. From what I can gather, the difference between the 1HP up-rated Superflo (30042) and the 3/4HP full-rated and 1HP up-rated Whisperflo variants (012430 and 012485) is the 1.5" plumbing port size on the Superflow and 2" on the Whisperflo. Is that it?

No, the impeller sizes are different and wet end performance/efficiencies are different (i.e. different head curves).

Also, the SuperFlo was developed to be competition for Hayward's SuperPump which is a smaller and lower end pump line. Both have 1 1/2" ports and both have about the same performance and efficiency. The WhisperFlo is intended to compete with Hayward's TriStar line of pumps. Again, a bit larger (i.e. higher head curve) at each rating vs the SuperFlo and have about the same performance and efficiency as the TriStar. The best way to compare two pumps is to compare their head curves. The higher the head curve, the more flow rate it will deliver for a given plumbing system but it will also cost more to run.

The prices are all over the place (even at the same dealers) so you can't go by price. Also, I see the single speed Superflo pumps have a Standard and High Efficiency versions while the dual speed and Whisperflo pumps do not. Are all the sual speed Superflo and all Whisperflo the high speed variants?

Two speed pumps in general use exactly the same wet end as the single speed counterpart. What is different, is the motor. A two speed motor has a second set of windings that are used for low speed so they cost a bit more.

Again, as I had suggested in the beginning, if you do not have any high flow rate requirements (i.e. a spa, large water fall, etc), the just get the smallest two speed you can find and it will end up being the most efficient and costing you the least amount of money to run (other than a VS pump). But if you want complete flexibility, just get a VS pump. It will save you the most amount in energy costs but costs a bit more up front.

 

[sktn77a]

Thanks. I'm going with the two speed pump for a simpler integration with the rest of my equipment. Cost isn't an issue but I just want the simplest way to make sure no-one turns on the Polaris booster pump without the main pump running on high. It more involved with the Superflo VS pump as all the timing controls are on the pump where they are not easily accessible to the booster.

So, the 3/4HP uprated Whisperflo (01245) is a higher end pump than the 3/4HP uprated Superflo (30042)? They have different wet ends, based on the different port size, but are there any other differences (impeller/volute)? How about the motors, are they the same?

 

[jblizzle]

The main pump does not need to be on high to run the booster pump. Low speed is fine.

 

[JamesW]

Probably the only thing that you will need high speed for is when you use the heater.

Low speed might not generate enough flow for the heater.

I would suggest that you choose the pump based on the total hp of high speed.

Total hp is rated hp x sf.

I suggest that you get a pump where the rated hp x service factor = 1.0 to 1.25 hp.

 

[mas985]

So, the 3/4HP uprated Whisperflo (01245) is a higher end pump than the 3/4HP uprated Superflo (30042)? They have different wet ends, based on the different port size, but are there any other differences (impeller/volute)? How about the motors, are they the same?

Everything is pretty much different (check part list in manual). Different wet ends and different motors. However, theoretically, since both use a 56y frame motor, it would be possible to find a single motor that would work on both wet ends as long as the THP was large enough to meet the requirements of both pumps. The motor is really not the main difference between these pumps.

The main difference between the pumps is the head curve and that has nothing to do with the motors and everything to do with the wet end design. Mostly, the impeller diameter and vane gap defines the shape of a head curve. And as I said before, it is the shape of the head curve that determines the efficiency of the pump. A lower flatter head curve will produce less flow rate but also use much less in energy.

I am not sure which WhisperFlo you are referring to, I don't see it on Pentair's web site, but as far as I know, the smallest two speed in the WhisperFlo line is the WFDS-3 or 24. That is a full rated 3/4 HP (WFDS-3) or the up rated 1 HP (WFDS-24) both technically the same pump just different ratings. Either pump would produce around 58 GPM @ 1.61kw. However, the SuperFlo 1 HP uprated pump (340042) would produce 53 GPM @ 1.35kw. The SuperFlo uses less energy mainly because it delivers less flow rate.