# Thread: 2 speed vs VS pump selection

1. ## 2 speed vs VS pump selection

Hi,

I need to order a new pump and I am narrowing down my selection. I live near Houston.

18000 gallon in ground with Spa
Hayward DE 60 sq ft.
Heater
in line chlorinator
Polaris booster pump PB4-60, Polaris 380

Here is my short list and logic:

1) Superflo VS 1.5hp uprated variable speed - the intermediate speeds will surly be enough flow for filtering, but will it be strong enough for the spa jets? I think high speed will be about 60 GPM. Built in timer saves the cost and installation of a two speed timer. I am concerned this pump might be a little cheap and not last as long as a Whisperflo.

2) Whisperflo 1.5hp full rated 2 speed (WDFS-6) - sized so the low speed will move at least 25 GPM. At high speed I estimate 90 GPM which seems more than enough

3) Whisperflo 1.0hp up rated 2 speed (WDFS-4) - I am concerned the low speed will not move enough water but high speed should be OK but not great.

This is all predicated on the total dynamic head which I guess is 50-60 at full flow. But I really don't know.

2. ## Re: 2 speed vs VS pump selection

Welcome to TFP!

What is your current pump? You want to make sure you match the performance curve so the spa flow is not reduced.

The Superflo is not a lesser pump than the Whisperflo. It is just smaller for people who don't need higher flow rates.

3. ## Re: 2 speed vs VS pump selection

Originally Posted by Chris43
This is all predicated on the total dynamic head which I guess is 50-60 at full flow. But I really don't know.
Each pump will have different head loss so it isn't wise to use the same head loss for every pump because it will lead to the wrong conclusion. You are much better off guessing which plumbing curve comes close to your plumbing situation.

Curve-A - Typical for 1 1/2" plumbing - Head Loss (ft) = 0.0167 * GPM^2

Curve-C - Typical for 2" plumbing - Head Loss (ft) = 0.0082 * GPM^2

To find the operation point for each pump, you plot the plumbing head curve on top of the pump head curve and see where they intersect. Kind of like this:

BTW, the Whsiperflo may not produce enough flow rate for the spa jets. As JB points out, you are best matching what you have now.

4. ## Re: 2 speed vs VS pump selection

Also, what are your electrical rates? Your electrical rates will help determine if the slightly more expensive VS pump will be able to pay back it's initial investment.

5. ## Re: 2 speed vs VS pump selection

My current pump is a Pac Fab 700 with 2 hp motor. I can't read the entire motor name plate so I assume it is 2hp uprated. I guess it is not putting out its rated GPM due to worn impeller because the spa jet velocity is not very high.

When I compare the pump curves of Superflo and Whisperflo it looks like the Whisperflow puts out at least 10% more flow with the same motor. I conclude that it is a more efficient design.

- - - Updated - - -

Right now power in Houston is reasonable at \$0.0926 per KWH.

6. ## Re: 2 speed vs VS pump selection

With the low power cost, a 2 speed mashes more sense, the added cost for a VS may never be recouped.

The Whisperflo will use more power to move more water so not necessarily more efficient.

I have not looked at the pump curves, but with a spa, I would guess you would be wanting to look at the 1.5HP Whisperflo 2 speed to have good action in the spa. The Superflo is likely too small.

7. ## Re: 2 speed vs VS pump selection

Originally Posted by Chris43
When I compare the pump curves of Superflo and Whisperflo it looks like the Whisperflow puts out at least 10% more flow with the same motor. I conclude that it is a more efficient design.
It is the wet end design including the impeller that determines the flow and head curve of the pump. Not the motor. The two pumps have very different designs and are suited for different applications. But the efficiency of the two pumps in terms of gallons pumped per watt-hr is about the same.

I guess it is not putting out its rated GPM due to worn impeller because the spa jet velocity is not very high
Has it ever been high? Have you ever inspected the impeller for blockage?

8. ## Re: 2 speed vs VS pump selection

Wow this is interesting. I look at your curves above and I took a pencil and paper and drew Curve C onto a blow up of the Superflo VS and Whisperflo curves from the Pentair web site.

Superflo VS = 35 GPM / 58 GPM / 68 GPM / 78 GPM at 1600/2600/3100/3450 RPM

Whisperflo 2 speed WDFS-4 1 HP Full Rated = 40 GPM low speed and 83 GPM High speed. Your curve above shows about 77 GPM for 1 URHP which I guess means uprated.

Whispefflo 2 speed WDFS-6 1.5 HP Full Rated = 45 GPM low speed and 90 GPM High speed.

To me this confirms the initial concern that the Superflo VS is not quite ideal at high flow for the spa.

Surprisingly the 1HP full rated is probably fine at low speed (35 GPM gives an 8 hour turnover) and OK at high speed. If I bypass the filter for spa mode it could be about acceptable.

But the Whisperflo WDFS-6 is only \$53 more than the WDFS-4 (today at Poolplaza) so it seems to be the best choice (given my pencil curve may not be too accurate it is best to have some safety margin)

The downside of the Whisperflo 2 speed units is that I don't have a two speed timer and the Superflo VS has a built in timer. There are a couple of low internet prices for the Superflo VS that make it tempting.

Does anyone have any ideas for a cheap solution to the 2 speed timer problem?

Thanks for the great info.

9. ## Re: 2 speed vs VS pump selection

According to the interesting graphic above that shows several pump curves together the Whisperflo moves more GPM than the Superflo at the same head with the same 1URHP motor. From this I conclude that the Whisperflo is more efficient. Are you saying the Whisperflo is drawing more power to move more water? Makes sense since it is doing more work.

Regarding the second point, I just moved into this house and I guess the pump is 10 years or more old. So I am just guessing the impeller is worn. It is really struggling to prime.

10. ## Re: 2 speed vs VS pump selection

You don't need a timer. Just use a 3 way light switch to manually select speed.

11. ## Re: 2 speed vs VS pump selection

This is precisely why you cannot size a pump by the label HP. It only has a very loose relationship to pump power. A 1/2 HP Whisperflo will generate more flow rate than a 1.5 HP MaxFlo.

Is this too much? http://www.amazon.com/Intermatic-P13...eed+pump+timer

Are you saying the Whisperflo is drawing more power to move more water? Makes sense since it is doing more work.
Yes

Regarding the second point, I just moved into this house and I guess the pump is 10 years or more old. So I am just guessing the impeller is worn. It is really struggling to prime.
That could be because the impeller is clogged.

12. ## Re: 2 speed vs VS pump selection

Why do you need a two speed timer? Normally you run a two speed pump on low speed nearly all the time and have a manual switch to switch to high speed if it is required. The only at all common exception is when you have a pool cleaner powered by the main pump, which often needs high speed to clean and then runs on low speed the rest of the time.

Impeller worn essentially never happens. Usually there is either an air leak or something blocking the impeller causing the symptoms you describe.

13. ## Re: 2 speed vs VS pump selection

I want timer to switch the pump to high speed when the Polaris comes on. Or, is it not necessary to be on high speed when the Polaris is running? I do have a booster pump.

14. ## Re: 2 speed vs VS pump selection

As long as you have a booster pump there is no need to be on high speed to run the cleaner. Low speed will deliver plenty of water to the booster pump and it will take care of the rest.

15. ## Re: 2 speed vs VS pump selection

I see lots of air in the basket. The lid is on tight. When I shut off the pump I see a little leak (not a spurt) at the suction side threaded fitting. I have put JB Weld WaterWeld on it which has helped. Is there something better to try to seal externally? Cutting the pipe and re-plumbing will be a half day job.

Is it possible that the pump shaft seal leaks air inward?

16. ## Re: 2 speed vs VS pump selection

Originally Posted by Chris43
Is it possible that the pump shaft seal leaks air inward?
No. The seal is on the pressure side of the pump so if that leaks, which sometimes they do, it will leak water outward.

Most air leaks are caused by the pump basket lid gasket and can be sealed with a little pool lube.

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