2-speed pump, or just a 2-speed motor?

[DaveAZ]

I have decided to replace my pool's single speed pump with a 2-speed.
My TDH is 42.5 with Kreepy Krawly operating and filter clean. On high speed (3450 rpm) I am looking for 63 GPM.

My existing pump is a 1hp Challenger with 56Y frame motor.
I have an Intermatic T104 timer and I already ordered a T106 for the 2-speed.

My initial idea was to look at pump curves for 2-speed pumps, find my matches, then buy only a matching 56Y 2-speed motor and re-use the rest of my existing pump. The price difference between a new pump and a new motor appears to be more than double with very little justification.

I found two drawbacks to this idea. The first is that 2-speed pumps have impellers that are designed for optimal flow at both 3450 and 1725 RPM, and no such impeller exists for the Challenger that I am aware of. The second drawback is that I can't seem to match up the motors to my selections at AO smith.

My ideal pumps thus far are: Pentair Superflo 340042 and Sta-Rite Supermax PHK2RAY6E-102L.
Both motors have the same specification: 1HP 230V 6.0/2.3 FLA. They both use Impeller part# 355067.
I still need to look at Hayward and Jandy pumps.

Any suggestions or advice?

 

[zea3]

How big is your pool? Do you have any water features the pump would need to run?

 

[Bama Rambler]

Just find a motor that the high speed SFHP matches the SFHP of the one you have now and you'll be fine.

 

[JasonLion]

The impeller is the same on a two speed as it is on the single speed of the same rating. All you need is a two speed motor that matches your current pump when it is on high speed and everything will be fine.

 

[dschlic1]

I have been down this road. My pool was built with a single speed Starite pump. The same basic model pump was also offered in a two speed version. Looking at the parts lists for the two pumps, the impellers for the single speed and the two speed had different numbers? I asked Starite what was the difference, and received a non-answer. I did purchase an AO Smith two speed motor and replaced the original single speed motor. I tried to find just the stator (the outside part of the motor), however could not locate one.
I have been very happy with the conversion, pump works great at both speeds. As a bonus the new motor is a high efficiency unit, so at high speed not only is electrical consumption down, but also the noise level!

 

[DaveAZ]

How big is your pool? Do you have any water features the pump would need to run?

No water features. Size of pool has been addressed in calculating GPM. (I'm at work and I don't have my calculations in front of me.) It should work fine at half-speed.

Just find a motor that the high speed SFHP matches the SFHP of the one you have now and you'll be fine.

Nope. My original pump was significantly oversized by the builder. They used the "rule of thumb" 50-60 for TDH and were way over. I did the TDH calculation and verified it with vacuum/pressure gauges- They did not. I prefer the energy savings of properly sizing it. I have no problem with selecting a pump from a pump curve.

The impeller is the same on a two speed as it is on the single speed of the same rating. All you need is a two speed motor that matches your current pump when it is on high speed and everything will be fine.

The parts diagram show different impellers. I'm betting that you are correct in that I can get by with the single speed impeller. I don't know if I will be getting the optimal flow at low speed without trying both impellers and comparing, so I'll never know what I'm missing.
(Edit: I looked again and it it the same part number. I got confused because they listed the impeller twice- once as a single speed and again as a two speed.)

I have been down this road. My pool was built with a single speed Starite pump. The same basic model pump was also offered in a two speed version. Looking at the parts lists for the two pumps, the impellers for the single speed and the two speed had different numbers? I asked Starite what was the difference, and received a non-answer. I did purchase an AO Smith two speed motor and replaced the original single speed motor. I tried to find just the stator (the outside part of the motor), however could not locate one.
I have been very happy with the conversion, pump works great at both speeds. As a bonus the new motor is a high efficiency unit, so at high speed not only is electrical consumption down, but also the noise level!

That sounds like the exact road I'm on. I thought the stator is included with the motor. My local pool store rebuilds pumps and has a full selection of stators available. I hope mine works out as well as yours did.

Thanks for the responses- it sounds like I'm on the right path!

 

[mas985]

Two speed pumps are usually uprated so when you look at part#s you need to take that into account. The impellers will be the same for the same THP (HP * SF) but not necessarily the same "Label HP".

 

[DaveAZ]

Two speed pumps are usually uprated so when you look at part#s you need to take that into account. The impellers will be the same for the same THP (HP * SF) but not necessarily the same "Label HP".

I have been approaching it by trying to match the motor electrical specifications given by the pump manufacturer. Pentair says it is 1HP 230V 6.0/2.3 FLA. So far I have not found a motor with matching amps, but I only looked at AO Smith thus far.

I have not found webpages with motor specs for Emerson or any other motor manufacturers. If anyone has links to post, I'd appreciate the leads.

 

[mas985]

THP is the better way to match the motor. I have found that the definition of maximum amps and FLA are not always consistent so you might end up with the wrong motor. However, what is consistent and most important is the THP. Also, your new motor can exceed the THP of the old by a little and still be fine.

At 6 FLA, that is probably a 1 HP uprated motor and a two speed motor that would work is a A.O. Smith B2980.

 

[DaveAZ]

THP is the better way to match the motor. I have found that the definition of maximum amps and FLA are not always consistent so you might end up with the wrong motor. However, what is consistent and most important is the THP. Also, your new motor can exceed the THP of the old by a little and still be fine.

At 6 FLA, that is probably a 1 HP uprated motor and a two speed motor that would work is a A.O. Smith B2980.

B2980 was the closest match that I had found thus far. I'm not convinced that it is an exact match, though.

 

[mas985]

It is a direct replacement. Why don't you think it is a match?

 

[Bama Rambler]

Dude, you're seriously overthinking this, If Mark says it's a direct replacement, slide your little plastic card in the slot and order it. It'll work perfectly!

 

[DaveAZ]

I think I found the flaw in my thinking. I'm expecting the same results from a Challenger pump as I see in the Superflo/Supermax pump curves.
Perhaps it is the difference in impellers, but to get my desired flow rate at my given head, I am not landing where I want to on the Challenger pump curve.

(I'm selecting 2-speed pump motor based on 63GPM and 42 TDH)


The Challenger High Flow pump curve shows a 3/4 HP moving [email protected].
The 1hp Challenger pump (OE with pool) is showing [email protected].

The SuperFlo & SuperMax curves show a 1 HP moving [email protected].

To use the Challenger High Flow pump with my application, I'm thinking I should have had a 3/4 HP impeller since the beginning.
Should I be trying to match the SFHP of the 3/4 HP challenger motor? (which I do not know) Does a 240V 2-speed 3/4HP 56Y motor even exist?

Buying an entire pump is sounding easier than swapping the motor with specific expectations...

 

[JasonLion]

What are you trying to do???

When replacing a motor, you match or exceed the motor that you currently have. The process depends only on the THP of the motor and has nothing at all to do with GPM or TDH.

I don't understand why you are even thinking about GPM or TDH. There is nothing in your pool description that appears to require any particular flow rate. In any case, you are not comparing the pumps correctly. TDH does not remain constant. The TDH will be different for every pump, and therefore the GPM will not be what you think it will be.

 

[mas985]

DO you have pump model # for the Challenger? Is there any information on the nameplate?

 

[DaveAZ]

What are you trying to do???

I was trying to Select a 2-speed motor for my pump that would give me 63 GPM at 42 TDH at high speed. I was assuming that I could re-use my impeller, but I cannot because my original pump was oversized.

When replacing a motor, you match or exceed the motor that you currently have. The process depends only on the THP of the motor and has nothing at all to do with GPM or TDH.

You are under the impression that I am only trying to replace a motor, which is not the case. The first thing I did was conduct a proper pump sizing calculation. I was hoping to only need to replace the motor with a 2-speed motor, but apparently I also need a smaller impeller to compensate for the fact that my original pump was WAY oversized.

I don't understand why you are even thinking about GPM or TDH. There is nothing in your pool description that appears to require any particular flow rate.

I don't want to continue to exceed 63 GPM when I have 1-1/2" Sch. 40 PVC on my discharge side. I also don't want to continue to exceed the filter data which says the max. GPM should be 72, since the ribs in the grids were frequently breaking at 88 GPM during backflushes ever since the pool was built.

In any case, you are not comparing the pumps correctly. TDH does not remain constant. The TDH will be different for every pump, and therefore the GPM will not be what you think it will be.

Not exactly. TDH is a constant based on your pool system as installed, discounting 23.1 ft./water difference between a clean filter and a dirty filter, and not including any adjustments one may make on their pool equipment.
The GPM output at a given TDH is different for every pump and with each impeller available for that model, and this is where the pump curves come into play and why the exact TDH of a pool system should be calculated prior to selecting a pump for each specific pool.
My mistake was looking at pump curves for a different model pump and thinking I could match the output with a different model of pump. I ignored the design differences between impeller, diffuser and volute. Luckily I caught on before buying the motor.

Do you have pump model # for the Challenger? Is there any information on the nameplate?

Yep. It is an old Pac Fab, but the equivelent of current Pentair #346204. Namplate: Motor B-168887 56Y frame 7.8-7.4/14.8A. http://www.pentairpool.com/pool-pro/pro ... mps-23.htm
To do what I want I would need to get a 3/4HP impeller and a 2-speed motor. It seems easier to sell this pump on craigslist and get a new pump.

 

[mas985]

Not exactly. TDH is a constant based on your pool system as installed, discounting 23.1 ft./water difference between a clean filter and a dirty filter, and not including any adjustments one may make on their pool equipment.

Sorry but this is not a true statement! Head loss in pipe, fittings and equipment is dependent on the flow rate through them. Higher flow rate results in higher head loss. If you change the size of the pump both the flow rate and the head loss will change.

There are two equations that need to be solved simultaneous to determine the operation point of the pump. The head curve of the pump is one equation and the plumbing curve is the other equation. The pump curved does not depend on the pump head curve and visa versa. However, these two curves are nearly orthogonal and cross at only one point, the operating point.

I would encourage you to read through the "Hydraulics 101" thread in my signature. There is an example of a pump head curve and overlaid plumbing curves. Also, the link called "PumpEd 101" is site that is very good and explains everything you would ever want to know about hydraulics and pumps. The articles are written by Joe Evans a PHD from Pentair.

As for your own situation, you would probably be better off going with a new pump unless you way to replace both the motor and the impeller which you can do.

 

[DaveAZ]

Not exactly. TDH is a constant based on your pool system as installed, discounting 23.1 ft./water difference between a clean filter and a dirty filter, and not including any adjustments one may make on their pool equipment.

Sorry but this is not a true statement! Head loss in pipe, fittings and equipment is dependent on the flow rate through them. Higher flow rate results in higher head loss. If you change the size of the pump both the flow rate and the head loss will change.

There are two equations that need to be solved simultaneous to determine the operation point of the pump. The head curve of the pump is one equation and the plumbing curve is the other equation. The pump curved does not depend on the pump head curve and visa versa. However, these two curves are nearly orthogonal and cross at only one point, the operating point.

I would encourage you to read through the "Hydraulics 101" thread in my signature. There is an example of a pump head curve and overlaid plumbing curves. Also, the link called "PumpEd 101" is site that is very good and explains everything you would ever want to know about hydraulics and pumps. The articles are written by Joe Evans a PHD from Pentair.

I was basing my statement on use of a single-speed pump where the flow rate is a constant because the impeller spins at 3450 RPM.

If you change the size of the pump both the flow rate and the head loss will change.

If I was using the same pump/impeller at 3450 RPM and only changed the size of motor without undersizing enough to affect performance, my flow rate would not change.

As for your own situation, you would probably be better off going with a new pump unless you want to replace both the motor and the impeller which you can do.

That's pretty much the conclusion that I have come to. It opens up my choices to a lot more pumps to choose from as well.

 

[JasonLion]

For a 13,300 gallon pool, using the common commercial pool requirement of three turnovers per day gives a desired pump flow rate of just under 28 GPM. Residential pools don't need anywhere near the flow rate required by commercial pools. In fact the flow rate requirement for a residential pool of 13,300 gallons is so low that other considerations, like being able to vacuum, become the dominant consideration, Any pump that will be able to vacuum the pool will provide more than enough water flow to satisfy the filtering requirements. At that point it becomes a question of getting the smallest pump you can that will still be able to prime, vacuum, and will work correctly with your filter, all of which are going to be at lower flow rates than your current 63 GPM target. Getting a pump larger than what you need will work, but it will use more electricity than you need to be using and provide no advantages.

 

[mas985]

I was basing my statement on use of a single-speed pump where the flow rate is a constant because the impeller spins at 3450 RPM.

But our discussion was about changing the pump size. And when you do that both the head loss and flow rate changes.

If I was using the same pump/impeller at 3450 RPM and only changed the size of motor without undersizing enough to affect performance, my flow rate would not change.

True, but my statement that you were commenting on was about a change in the pump size.

However, if you simply change the motor to a two speed, you can still save quite a bit of money. While high speed will still use the same power. On low speed, a two speed pump will use about 1/4th the power as high speed but the flow rate will only drop by 1/2. So your net savings for the same number of turnovers is about 50%.

The Pentair Challenger 346204 is a 1 HP up rated pump with a SF of 1.25 for a THP of 1.25. The motor I orignally suggested, A.O. Smith B2980, is a perfect fit for your existing impeller and would still allow you to save both energy and money.