Help with Pump Replacement

[NoFishInPool]

Can I get some help (i.e., recommendation(s)) on pump replacement?

We have an inground pool (about 32,00-35000 gal) that may be 40-50 yrs old. Recoating starting today (yay!) I have read the Hydraulic 101/Pump Basics postings and appreciate that information but there is still a lot I don't quite understand. The original pump when we bought the house (and pool) seven years ago was 1.5 HP with SF of 1.47 = 2.2 SFHP (220 V). When it went out a little more than a year ago, I replaced it with a 1.5 HP with SF of 1 = 1.5 SFHP (should have read TFP Pump Basics then)...must admit budgetary constraints at the time influenced me...). ~Weak pump that would not pump effectively when filter pressure went up at all. Filter - DE6000 (DE, 60 sq ft, 120 gpm design flow rate). I don't know much about the piping below the concrete. A basic guess is that there is about 207 ft of piping on the supply side and 193 ft on the return side. Max depth is 9 ft. Rough calculation is 97 ft of head...? My question, of course, is - what pump should I buy to replace the cheap pump? I am thinking about SFHP=2, two speed seems most economical to operate...any suggestion?

We have a lot of trees around and end up with a fair bit of organic material (leaves, pollen, catkins, etc.) that requires more attention but will also competes for chlorine in the pool. I do mainly use the BBB approach plus some tablets to supplement (mainly when I travel).

Thanks for the input!

 

[mas985]

Weak pump that would not pump effectively when filter pressure went up at all. Filter - DE6000 (DE, 60 sq ft, 120 gpm design flow rate).

Weak is good. You don't want a pump to blast through a dirty filter and ruin it. Low and slow is much better for filtering.

DE6000 (DE, 60 sq ft, 120 gpm design flow rate).

Ignore that. That is an upper limit. Again, slow is better.

I am thinking about SFHP=2, two speed seems most economical to operate...any suggestion?

Don't do it. Bad decision.


I run my 20k pool on a 1/2 HP pump. That's right, 1/2 HP. Nearly any pump is sufficient for circulation.

Your current pump, IMHO, is too large, not too small. Your problem may be to maintenance or chemistry.

So a few questions.

Are you following the TFP guidelines to clean your filter when the pressure gauge is only 25% above clean temperature?

How often are you cleaning the filter?

What is the CYA level in your pool and what is the FC level right before adding chlorine?

 

[NoFishInPool]

Thanks for your reply mas85. A few answers and and more question...always more questions!

Weak is good. You don't want a pump to blast through a dirty filter and ruin it. Low and slow is much better for filtering.

I run my 20k pool on a 1/2 HP pump. That's right, 1/2 HP. Nearly any pump is sufficient for circulation.

I did read that but was concerned because with my old pump, I could feel a pretty good water flow through the eyeballs; with my new pump, I could hardly feel flow at all even when it was new and filter was clean. (Installed new filter grids at the same time that I put in the new pump.) With the old pump, I had put in a "Circulator" - it seemed to improve mixing and reduced pump run time but with the new pump, there is not enough pressure to make it turn.

It seems to me when I look at pump performance curves, if I do in fact have almost 100 ft of dynamic head, most smaller pumps don't pump - even many 1.5 HP pumps only seem capable of pumping 5-10 gmp - not enough to turn over the pool in the 8 hrs or so that folks (and Pump Basics) talk about...?

Are you following the TFP guidelines to clean your filter when the pressure gauge is only 25% above clean temperature?

I am backwashing when the pressure goes up about 25% above the clean pressure - with the old pump with was from about 22 psi up to 27 or so; with the new pump, clean pressure is only about 12-15 psi and (backwash at 18). It didn't see to take long to get to that point. I did just take the filter apart to clean and found lots of DE and algae (although the pump hasn't been running for a couple of months). I do suspect that my algae problem last summer contributed to the low throughput.

What is the CYA level in your pool and what is the FC level right before adding chlorine?

Pools was emptied this morning for new pebble coating but CYA was typically maxed out (50?) from the previous owner and my first 2-3 yrs of chlorine tablets, until I discovered this website. I am not sure about the FC level but I did have a recurring problem with algae, partly attributed to the degraded plaster. It was difficult to keep the chlorine level high enough to kill the algae. I expect that to be resolved with the new coating and more attention this season to brushing and bleach.

Thanks for sharing your expertise.

 

[mas985]

not enough to turn over the pool in the 8 hrs or so that folks (and Pump Basics) talk about...?

That is another thing to ignore. Turnover is not a very good indicator of water quality. Many pools can achieve excellent water quality (i.e. sanitation) in as little as a 1/20th of a turnover. So it is not a very good metric for determining run time.

Since you are on bleach with a robot, I bet you could get away with only 2 hours of run time or even less.

with the new pump, clean pressure is only about 12-15 psi and (backwash at 18). It didn't see to take long to get to that point.

That is usually an indicator that the FC level is not high enough and algae is clogging the filter. Using bleach, it should be kept at 10% of CYA or higher.

 

[kadavis]

How did you come up with 100ft of head figure. There's really no pool pump that operate at that resistance. Maybe a picture of your equipment set could help.

 

[kadavis]

swimming pool hydraulics - Bing, scroll down to the PDF Hayward Hydraulics and pump sizing. In there you can find how to figure your head out

 

[NoFishInPool]

Thanks, kadavis, for pointing out my confusion: - D - which I freely admit to - My original calculations were based on some tables I found estimating head based on my estimates of unknown (underground) piping - estimated at minimum of 207 ft of 2 inch pvc on supply side and 193 ft (2 inch) on the return side (plus presumed 90s where lines would turn). For whatever reason the previous owner used a pump with 1.5 in. inlet and outlets, multivalve is 1.5 going into filter...assorted reducers in above ground piping to make things fit.
Other things I know:
1 main drain
2 skimmers (seem like outlets may be 1.5 inch but pipes coming above ground to splitter valve are 2 in. reduced to 1/5 for pump)
4 working returns
2 returns (maybe one for vac?) plugged or not operating.

How did you come up with 100ft of head figure. There's really no pool pump that operate at that resistance. Maybe a picture of your equipment set could help.

Thanks for steering me to the Hayward Hydraulics booklet. I don't have a pump that is operating (so can't measure supply side) but if I use the example estimate (2/3 size of my pool) for their supply side and I add up my turnover rates and pipe flow rates - I come out with something like 50 - 56 TDH (hopefully much more reasonable than 100). That puts me at needing 70 gpm @ 56.1 TDH (max) as parameters to look up on the pump performance curves. I am thinking of variable speed or variable flow (didn't realize until reading more in the forum that there are both types (again thanks to earlier mas985 forum posts) but budget is of some concern. Mark (mas985) suggested 3/4 HP based on my original post; if I look at perf. curves for Whisperflo (just as an example) the ~60 TDH and 70 gpm suggests a 1 HP would work. Variable speed pump option might make the 1 HP all fall in line with Mark's comment that 8 hr turnover is not really needed, if operating mainly at lower speeds.

Please keep the clarity and suggestions coming?

 

[mas985]

You really needn't be concerned with head loss and flow rates. Again, for your setup nearly any pump is going to work fine.

However, I think your issue is with your chemistry and not your pump. A common misconception. I would get that in order before deciding on changing any hardware.