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

[DaveAZ]

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.

Exactly. Since I am selecting for two speed, I am looking for the maximum that the pool is designed for at high speed. The 63GPM target is intended to get my half-speed at around the 28 GPM you mentioned, and I am basing that on the Kreepy Krawly manufacturer's statement that it's minimum operating requirement is 25-28 gpm. (They told me this on the phone.)

I'd love to be able to calculate the TDH at 1725 rpm. The Hydraulics 101 didn't establish how I would create a plumbing curve to do that and I have no idea as to how people are able to use the low-speed portions of the pump curve without it.

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.

I think I could still get away with dropping it to a 3/4HP impeller in order to stop slamming my grids and breaking ribs during backflushes, too.

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

but if you are selecting the new pump based on the point in the curve of your given TDH and expected GPM, you should get what you are looking for. Either that or my continuity of the conversation is getting very screwed up.

 

[mas985]

I'd love to be able to calculate the TDH at 1725 rpm. The Hydraulics 101 didn't establish how I would create a plumbing curve to do that and I have no idea as to how people are able to use the low-speed portions of the pump curve without it.

Actually, the third post has a spreadsheet that allows you to do just that. But again, I think what you really want is to determine what the flow rate is which the spreadsheet will also do.

I think I could still get away with dropping it to a 3/4HP impeller in order to stop slamming my grids and breaking ribs during backflushes, too.

I don't think you understand. You have an up rated pump which means you already have a 3/4 HP impeller. A 1 HP uprated pump is identical in performance to a 3/4 HP full rated pump in the same model line.

but if you are selecting the new pump based on the point in the curve of your given TDH and expected GPM, you should get what you are looking for.

Only if that point exists on another pump head curve which would be rare. You are making this much harder than it needs to be so let me make a suggestion:

First, you need to determine your current plumbing/pump operating point with some level of accuracy. You gave some numbers but did not explain how you got to head and flow rate. So if you can answer the following questions, I can then tell you the operating point for nearly any pump on the market using the PumpTools spreadsheet.


Distance measured between the pool and the pump (ft)?
Suction Pipe Diameter (1.5" I think)?
Number of suction pipes running from the pool to the pump?
The pump height relative to the pool water height?
The filter pressure (PSI)?

With this information, I can determine your plumbing curve which can then be overlaid on top of any pump head curve to find the operating point at high speed and low speed.

Note too that if you know the operating point of high speed, low speed can be determined by using the pump affinity equations.

Low Speed GPM = High Speed GPM / 2
Low Speed Head = High Speed Head / 4

 

[JasonLion]

The 63GPM target is intended to get my half-speed at around the 28 GPM you mentioned, and I am basing that on the Kreepy Krawly manufacturer's statement that it's minimum operating requirement is 25-28 gpm. (They told me this on the phone.)

You could save a significant amount on electricity if you got a pump that was around 30 to 40 GPM on high speed, and ran it on low speed when you were not using the Kreepy Krawly.

 

[mas985]

Jason,

I don't think there is a IG pump on the market that will do that. The smallest two speed that I know of will produce about 51 GPM on high/25 GPM on low even with the worst plumbing (CEC Curve A).

 

[JasonLion]

The smallest two speed that I know of will produce about 51 GPM on high/25 GPM on low even with the worst plumbing (CEC Curve A).

Fair enough. The point still holds however, get the smallest possible pump that is still at least 30 GPM on high speed, instead of getting a pump which is at least 30 GPM on low speed, and you will save on electricity.

I suppose the exception to my reasoning would be if the Kreepy Krawly was running the majority of the time, then you would be forced to run at high speed, which would be too high in my model, most of the time.

 

[DaveAZ]

First, you need to determine your current plumbing/pump operating point with some level of accuracy. You gave some numbers but did not explain how you got to head and flow rate. So if you can answer the following questions, I can then tell you the operating point for nearly any pump on the market using the PumpTools spreadsheet.


Distance measured between the pool and the pump (ft)?
Suction Pipe Diameter (1.5" I think)?
Number of suction pipes running from the pool to the pump?
The pump height relative to the pool water height?
The filter pressure (PSI)?

With this information, I can determine your plumbing curve which can then be overlaid on top of any pump head curve to find the operating point at high speed and low speed.

Note too that if you know the operating point of high speed, low speed can be determined by using the pump affinity equations.

Low Speed GPM = High Speed GPM / 2
Low Speed Head = High Speed Head / 4

Ok, here is my plumbing information I gathered for a pressure loss calculation and my gauge readings:

Suction side has two runs:

Run#1:
Kreepy Krawly
15' flexible hose
33' 2" Sch. 40
(3) 2" elbows

Run#2
Skimmer
20' 2" Sch.40
(3) 2" elbows

Both suction runs bullhead into a 2" manual diverter valve.
Diverter valve is set to minimum required for cleaner to operate.
(there is a tap to put a vacuum gauge on the cleaner side of the diverter.)

<pump>

Return side:
(3) 2" elbows between pump and filter
Filter (36)
2" Backwash valve
Approx. 90' of 1-1/2" Sch 40. with unknown fittings
(4) 1" Jets

Givens:
Max. flow is limited by 1-1/2" Sch.40 PVC @10' per second. (63 GPM.)
30 GPM is the filter's minimum flow rating.
Kreepy Krawly wants 25-28 GPM to operate.
220V power
Differential elevation is under 1' from top of water to bottom of pump.

Minimum flow calculation:
13,300 gallons / 7 hour turnover rate= 1900 GPH/60= 31.6 GPM (Desired flow rate at half speed)

Gauge readings:
14 PSI at top of filter with filter freshly cleaned and loaded with DE.
09 in. mercury with Kreepy Krawly operating, reading taken at drain plug of pot strainer.
(07 in. mercury without Kreepy Krawly.)

My operating intent is to set the timer to start the pump on high speed so it will prime properly for the minimum time allowed (30 minutes? I don't have the 106 timer yet to see) and to have it run at half speed with the kreepy krawly operating for the remainder of the time.

 

[mas985]

Gauge readings:
14 PSI at top of filter with filter freshly cleaned and loaded with DE.
09 in. mercury with Kreepy Krawly operating, reading taken at drain plug of pot strainer.
(07 in. mercury without Kreepy Krawly.)

Since you measured both pressure and vacuum, I can use that instead of your plumbing description. I estimate that with your current setup and the KK operating has an operating point of 68 GPM @ 46' of head. (Note that to calculate head from those measurements you must take the filter height into consideration).

If you were to replace the motor with a two speed, the high speed operating point would not change and on low speed, the operating point would be around 34 GPM @ 11' of head.

However, since you are drawing from both the skimmer and the KK, that 34 GPM would be split between the two. If you want to run the KK on low speed, you will probably need to run 100% on that port to get the target flow rate. Doing so, will increase the suction head loss and therefore, you may not get 34 GPM. If you can measure the suction again but with just the KK engage and no draw from the skimmer, I can then tell you if there will be enough flow rate for just the KK alone. This would be worst case but at least you would know if it worked at all.

 

[DaveAZ]

If you can measure the suction again but with just the KK engage and no draw from the skimmer, I can then tell you if there will be enough flow rate for just the KK alone. This would be worst case but at least you would know if it worked at all.

22"HG.
16 PSI at top of pump.

(Note that to calculate head from those measurements you must take the filter height into consideration).

3' X 0.43 (gravity) = 1.29 PSI x2.31= 2.979. My TDH calc was three short.

 

[mas985]

Static head is one for one. So 3' high is 3' in head. 0.43 is truncated and should be the same as 1/2.31 = 0.432713.

But something does not make sense about your measurement. A higher suction should result in lower PSI. You should have less than 14 PSI.

 

[DaveAZ]

I took the PSI reading before I set the diverter to full KK.
Do you need the PSI while the diverter is full KK? I coud do it again...

 

[DaveAZ]

I estimate that with your current setup and the KK operating has an operating point of 68 GPM @ 46' of head.

That looks like you used the 3/4 HP curve. That would actually be a reasonable selection for this pool.

The Pentair Challenger 346204 is a 1 HP up rated pump with a SF of 1.25 for a THP of 1.25.

My existing equipment has a 1HP impeller and the side of the housing front is marked 1HP. For the purposes of their curve, 1HP applies, not 3/4 HP . Shouldn't that be 84 GPM @ 46' of head?

 

[mas985]

The pump model # you gave is for a 1 HP UPRATED pump. If you had a full rated 1 HP impeller, your motor would have burned up long ago. Have you taken apart the pump to read the impeller part#?

A 3/4 HP full rated pump uses the same impeller as a 1 HP uprated pump so the will have the same head curve. The brochure on the Pentair web site has only the full rated pump curves so you must use the 3/4 hp curve.

Do you need the PSI while the diverter is full KK? I coud do it again...

Yes but give me both PSI and in hg before and after you have full kk.

 

[DaveAZ]

<deleted>

 

[DaveAZ]

I had my pool store pull the cover and verify the impeller part number the last time I brought it in. It is the 1hp impeller. It never burned up, but it has needed lots of repairs such as bearing and stator replacements.

A 3/4 HP full rated pump uses the same impeller as a 1 HP uprated pump so the will have the same head curve. The brochure on the Pentair web site has only the full rated pump curves so you must use the 3/4 hp curve.

This makes no sense to me. If it is marked as 1hp and has a 1hp impeller, why would having a slightly weaker motor suddenly jump it's performance down to an entirely different profile that matches the 3/4hp curve? Everything else I am reading says that the pump design dictates its output as long as the motor speed is constant at its 3450 RPM.

I'll be able to set up the vacuum gauge and take readings again tonight.

 

[mas985]

You really should spend some time reading up on pumps and motors and how they are labled. This is well known issue with the industry and leads to a lot of confusion. So if you don't believe me, then you might want to read up on it. Here are a few articles:

http://www.poolplaza.com/pump-ratings.shtml
http://www.poolsupplyworld.com/blog/Gen ... motors.htm
http://www.inyopools.com/guide_pool_mot ... ement.aspx

Also, if you look at the Challenger manual on page 12, you will see a parts list and in that list part way down on item #5, you will see a part# for an impeller but two different HP numbers next to each impeller. The first is for a full rated motor and the second is for the up rated version. For example,

Part # 35-5187 shows "IMPELLER-3/4F, 1A" which means that this impeller is for the 3/4 HP full rated motor and also for the 1 HP up rated motor (see page 4 for definitions). Same Impeller two different rated motors. However, even though the motors have different lable HP, they have the same THP so essentially, they are the same strength motor. This is why you cannot just go by the label HP. You must also include the service factor so you can then determine the true HP of the motor.

Look at this page from Pentair: http://www.pentairpool.com/pool-owner/p ... mps-24.htm

On the Specs tab, note that the 345203 and the 346205 have the same SFHP (or THP) but their label HPs are different. The first is a 3/4 HP full rated pump while the second is a 1 HP up rated pump. This means that they both have the same impeller.

Do YOU actually have the impeller part#?

If you call up Pentair or any parts store and ask them for the impeller part# for the Pentair Challenger 346204, I bet it will come back as a 3/4 HP full rated/1 HP uprated impeller.

 

[DaveAZ]

I'm willing to get the number off of the impeller. I might be able to do that tonight as well.

Considering mine is an old Pac Fab, it may or may not be identical to the pentair part number unless you used the data I which pulled from the motor to verify. It has also been in and out of the pool store enough times that I don't know if the impeller was ever changed out.

Thanks!

 

[mas985]

Another way to tell is to look at the motor label service factor if you can read it. If the motor label states that the motor is rated at 1 HP with a service factor of 1.25, then it can only support a 3/4 HP full rated/1 HP up rated impeller. Anything larger would have burned out the motor.

 

[svenpup]

I scanned through your posts and I feel like you may be over thinking it, but more knowledgeable people than me have already weighed in.

Last year I swapped my old 3/4 hp for the A.O. Smith B2980 (documented here) and love it. I got a Tightwatt2 to control it and soon afterward added a Pool Pilot Digital Nano SWCG. I only run on high when I am running my cleaner booster pump. Otherwise it runs on low along with the SWCG.

 

[DaveAZ]

Today's update: The haboob had packed my filter with dirt overnight, so I had a good reason to start with a clean filter for my readings.

The new readings at full KK: -22"Hg with 3-4 psi at the top of the tank.

With the diverter wide open to both:
17PSI@ top of tank
-5"Hg at housing front.

Pump the pool came with (update):
Impeller number: 35-5369. The exploded parts diagram says: "Impeller-1F, 1 1/2A"
The pool was built in 1992 and per the internet that impeller wasn't available until 11/1994. It must have been changed at some point.

I found a small silver sticker on the housing front. it reads: CHII -N1-1FE 2-13-A02
The correct Pentair equivelent part number is 345205.
(My pool store gave me the wrong pentair number, which they based on only seeing the motor.)
The motor is marked as made for Pac Fab by Magnatek and BJ-11-224.

I may be overthinking it, but I'd rather do my homework and get the best possible sized motor and/or pump to accomplish the job that I'm attempting with the least electricity use. I'm also thankful for the experienced outside help.

 

[mas985]

Ok now that you have the pump figured out, there is another issue.

With a pump that large I would have expected a lot more head loss on 2"/1.5" plumbing. 48' of head loss is very low for 1.5" plumbing and would put the flow rate at 90 GPM. Is there only a single 1 1/2" return line from pool to pad or are there actually 4 separate return lines that split at the pad, one to each eyeball?

Also, the other thing that doesn't make sense is that when you have the KK fully engaged, you have less head loss than when you have two suction ports, 37' of head vs 48' with both suction ports open. That is impossible so one or more of the measurements must be incorrect. Because of the excess head loss on the suction side, this makes the pressure readings very low so I suspect there is a lot of error in the pressure reading. Are you confident that both gauges are opearting correctly?

At this point, I can't tell you what is going on since nothing seems to make sense.

Have you thought about a VS pump? In situations such as this, it takes the guess work out of things. Of course it costs a lot more too.