Questions about 2-speed pump

[Pleakpool]

Hi, new member here. Been lurking a while and finally joined last week. I hate that my first post is a question, but oh, well.


Have a 24' ABG (approx 14,000 gallons). Got in on craigslist last year. It was a baquapure system, which we are not using. Have a Goldline aquatrol swg as sanitizer. Pump is starting to die. It and the sand filter are branded baquapure. After digging around, I believe they are Waterway brand as this

http://www.waterwayplastics.com/OwnManB ... andFil.pdf

looks exactly as the setup I have. the sand filter is 26" with 200 lbs of sand. The pump is a 2.5 HP two-speed. Run it on timer 10-12 hours a day on low spped - only use high speed for backwash and the pool cleaner.

In estimating around 30 feet of head for my setup, I was looking at the Hayward Super II pump (3/4) hp. It puts out a little less than 60 gpm at 30 feet. Which should turn over my pool in about 4.5 hours. The guy at the local pool store told me down here (Houston) I need to turn it over at least twice a day. At 11 amps for the Super II, that gets costly. My old pump ran at 4.4 amps on low speed, and I ran it for about 10 hours a day and water was fine. I don't know the gpms unfortunately.

Does anybody know of a 2-speed pump that would put out at least 30 gpm at 30 feet of head? The pools stores around here are pushing only 1 speed pumps. One even told me you don't want a 2-speed pump down here - is there a valid reason for that?

 

[Poolsean]

Most residential pools run with a minimum of one turnover per 8 hrs. Based upon that figure, you'll need a minimum of 30 gpm. A 1/2 or 3/4 hp pump will do that easily. You will have better filtration and chemical circulation the longer your pump run times, or the more turnovers you have. So upsizing it is not a problem. You will have to consider the flow rate requirements for the cleaner too. What type do you have?
It seems like cost of operation is a factor for you, correct?
Two speed pumps have their merits. You will need to consider the low speed flow rate, plus the high speed flow rates to ensure you get proper circulation. When considering 2-speed pumps, it doesn't need to produce 30 gpm at 30'head to be the correct size. Determine how many hours per day your cleaner will be in operation. Backwashing should not be factored in.
Determine how many gallons per day is circulated during our high speed cycle. The determine what flow rate you need for the rest of your run time for low speed.

example. If you're running your cleaner 2 hrs/day on high speed @ 75 gpm, you'll turn over 9,000 gallons in the two hours. That leaves 5,500 gallons to circulate. IF you decide you're going to run low speed at 6 hrs/day (total 8 hrs per day), low speed will need to put out at least 16 gpm. One complete turnover in an 8 hr cycle with a two speed pump.

Is there any valid reason for not wanting a two speed pump in Houston? I don't think there are any unusual reasons that would disqualify a 2 speed pump there. You need to circulate water. Using a one speed vs a two speed is mostly based on operating costs, water features, cleaners, heaters, and hydrotherapy action requirements.

In fact, Pentair Intelliflo is doing a great deal of business with the multispeed pump.

 

[Pleakpool]

Thanks for the quick reply. I'll try to answer all the questions.

Most residential pools run with a minimum of one turnover per 8 hrs. Based upon that figure, you'll need a minimum of 30 gpm. A 1/2 or 3/4 hp pump will do that easily. You will have better filtration and chemical circulation the longer your pump run times, or the more turnovers you have. So upsizing it is not a problem. You will have to consider the flow rate requirements for the cleaner too. What type do you have?

I have a Manta pool cleaner by Zodiac. It's a suction cleaner that attaches to the skimmer. I probably only run it 2 hours a week if that - just when pool is dirty - from pollen, leaves, etc. The pool has stayed extremely clean for the most part.
I have no idea what it's flow requirements are, I just know that on low speed with the pump I have, it doesn't work well, but on high speed it works great.

It seems like cost of operation is a factor for you, correct?

Very much so. We have such a long season here and rates have become ridiculous. I wanted two speed because of the lower current draw. I am looking for a pump that does everything. Low capital cost, good cleaning/circulation, low electricity usage. :-D

Two speed pumps have their merits. You will need to consider the low speed flow rate, plus the high speed flow rates to ensure you get proper circulation. When considering 2-speed pumps, it doesn't need to produce 30 gpm at 30'head to be the correct size. Determine how many hours per day your cleaner will be in operation. Backwashing should not be factored in.
Determine how many gallons per day is circulated during our high speed cycle. The determine what flow rate you need for the rest of your run time for low speed.

example. If you're running your cleaner 2 hrs/day on high speed @ 75 gpm, you'll turn over 9,000 gallons in the two hours. That leaves 5,500 gallons to circulate. IF you decide you're going to run low speed at 6 hrs/day (total 8 hrs per day), low speed will need to put out at least 16 gpm. One complete turnover in an 8 hr cycle with a two speed pump.

Since I don't run my cleaner daily, if I could find a pump that ran only 30 gpm, it seems like that would work. All the pumps I have found though seem to flow more than that (and thus use more electricty) And when I was looking at the flow charts for two-speed pumps, it seems like that on all the pumps, they topped out at less than 30' of head pressure. SInce I have the sand filter - that seems it would preclude a low speed pump.

In fact, Pentair Intelliflo is doing a great deal of business with the multispeed pump.

I would love to have that, but I priced one and it violates the capital cost requirement.

 

[JasonLion]

Dynamic head varies depending on the flow rate, and for a give pump flow rate depends on head. It can be rather confusing.

You don't want to use the 30 ft of head number when calculating low speed. Instead calculate high speed and then figure that the flow rate on low speed will always be half as much as the flow rate on high speed. On low speed the pump will use just a little more than one quarter as much electricity. Any of the two speed pumps, 3/4 HP or above, should be fine.

 

[Pleakpool]

I agree - calculating head can be a nightmare. Especially when you have older equipment that you can't find any specs on.

So what you are saying is that I use my 30 ft of head. And looking at the performance chart for a Pentair Superflo, the 3/4 hp on high speed looks to be putting out around 60gpm. So I could assume that on low speed, it would flow in the neighborhood of 30gpm? Because on their chart, all of the low speeds zero out at somewhere between 15-20 ft. That's what was throwing me off. According to this chart, I could get by with even a 1/2 hp - at 30 ft, it appears to flow in the neighborhood of 50gpm on high speed.


Am I mixing up static head vs. dynamic head? i.e. - the 30 ft assumption is dynamic head - which takes into account the gpm flowing through it. So less gpm = less dynamic head. Is any of this paragraph at all correct? :?:

 

[JasonLion]

Yes, you are getting the idea. Static head is the same at all flow rates, while dynamic head increases with increased flow rate.

The reason I said that you should get at least 3/4 HP is that your current 2.5 HP pump on low speed should be giving 5/8 HP and you said that wasn't enough for the cleaner. Now, not all 1/2 HP pumps are the same, so an efficent 1/2 HP pump will probably be fine, but a lower efficency 1/2 HP pump wouldn't run your cleaner as well as you would like.

 

[mas985]

Pleakpool,

How do you know you have 30' of head? Seems a bit low for a 2.5 HP pump.

What is your filter pressure reading on high speed and low speed for your current pump?

 

[Pleakpool]

Pleakpool,

How do you know you have 30' of head? Seems a bit low for a 2.5 HP pump.

What is your filter pressure reading on high speed and low speed for your current pump?

It was a ballpark figure. I read it at
http://www.poolplaza.com/pool-pump-sizing-2.shtml

and a couple of other places - and since I don't have solar panels or any other restrictions besides the swg and filter, that what I was using. Surprisingly, even the local pool store guy used 30 ft as an estimate.


Pretty sure my gauage is not working correctly - also will be changing that when I get new pump. But before current pump troubles, low speed was 3-4 PSI and high sppeed was a little under 10 psi

 

[Pleakpool]

Has anybody ever used AquaFlo pumps? I found the following:

http://www.pumpwarehouse.com/aquaflo.htm

performance curves. I was looking at the 3/4 HP FMHP - at 30 ft. of head in puts out a little more than 70gpm and and 35 ft - 65 gpm. If I cut that in half for running at low speed - I'm looking at a little less than 8 hour turnover.

I called Aquaflo - the 3/4 hp FMHP runs 8.8 amps at high speed and only 2.6 on low. That's excellant! Two year warranty (+3 year prorated after that). ANd they are cheap. Now the question is - do they last- anybody ever used one - this sounds almost too good to be true.