Help choosing and sizing a filter

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TFPJules111

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Aug 16, 2007
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Denton, TX
For anyone who's followed the story so far: Homeowner - 0, First American Home Warranty Co - 1

They're denying my claim because the old filter was repaired "improperly" (ie. epoxy) by the previous homeowner, instead of having the (obsolete, not available) part replaced. On the plus side, I get to put in whatever filter I want. On the negative, I also have to pay for it.

I've studied the different types and I'm leaning toward sand or DE - more towards sand. From what I've read, it looks like there's less maintenance with sand and no hazmat DE.

Pool size ~13000 gal. I have a whisperflo 1 1/2 hp pump. I've used the hayward pump/filter sizing worksheet http://www.haywardnet.com/pdfs/Pump_filter_sizing.pdf to come up with a 22-27 GPM turnover rate (8-10 hour). Based on the worksheet, I have about 36 ft of head. In this post, http://troublefreepool.com/viewtopic.php?t=2581, Dave suggested using 45 ft of head to calculate pump GPM.

Based on Pentair's pump curves for this model 45 ft of head = 118-120 GPM and w/ 36 ft of head = 130 gpm

That seems grossly oversized for this pool, but I understand the $$$ incentive of pool stores to "upsell" stuff.

In that same post Dave says:

Your filter size should be in relations to your pump's capacity to push your water. If your pump is rated somewhere around 50-70gpm, a filter size about 20% bigger than that would be okay. Larger filters are generally better. For sure, do not get one rated less than your pump.
Click to expand...

When I look at the technical specifications for Hayward Sand Filters (just an example, haven't settled on brand or type) it seems like I'd have to get a HUGE filter.

Am I misunderstanding pump/filter sizing guidelines? Do I need a smaller pump?

What filter types (cart, sand, DE) do you folks like (and why)?

What brand & model would you recommend?

Thanks.
 
You are to be commended for your dilligence. You have done your homework well. Yes, your current pump is too much for your pool. A 3/4 hp 2 speed pump (low speed for energy savings and filtering, high speed for vacuuming) should be all you need if you have no special water features. I would choose the 24" 300# sand filter. This is somewhat oversized, but for some reason you can usually find them cheaper than the 21-22" 200# filters. This would probably lead to lees frequent backwashing.
 
Do you know the pipe sizing? I would imagine that your head is probably higer than you think. That is a pretty stong pump and if you want to keep it then I would go with the 31" side mount hi flow filter. This is an expensive route. :( I think that you could replace the pump and use the 24" filter for less money than just buying the 31" filter. Your pump is sized for a pool twice your size. Sorry for the bad news.
 
You can usually get away with exceeding the flow rate of the filter by a little but I wouldn't try a combination that has double the flow rate of the filter. Even if nothing is damaged you will still have inferior filtering. You should either get the huge filter or a smaller pump. The smaller pump will also save you a significant amount of electricity, paying for it's self in a couple of years.
 
Thanks for all of your help.

@ Matt 633: pipe sizing to and from the pool is 1.5". Pipes between pump, filter, pressure cleaner are all 2"

You guys bring up a good point about replacing the oversized pump. Energy savings is appealing. I'll price both the huge filter, no pump & 3/4hp 24" filter options.

It looks like just replacing the pump motor is a lot less expensive than replacing the entire pump. I'll check the whisperflo manual for specs. If the 1 1/2 HP & 3/4 HP use the same volute (is that the right term?) then I could just replace the motor and save some $$$.

Can you enlighten me on the benefits/drawbacks to top vs. side mount valves? Is it about mounting convenience or reducing the head?
 
Jules, I think the side mount vs top mount is more related to the size of the filter than anything else. I have nothing to back that up....just seems like the bigger ones are side mount.

Either of the options you're considering will work. The big pump and filter would require a little less maintenance but burn a lot of electricity.
 
Thanks Dave. Thanks for the test kit also - very clear instructions, glad I chose your kit.

It looks like I can fit a 3/4 HP 2 speed motor to my existing pump head. I'm going to check with Pentair tech support to see if I need to change the impeller - the manual shows different parts for each HP.

Anyone have experience doing this type of down-sizing modification (or motor replacement) that can offer tips? It appears to be as simple as removing 4 bolts, replacing the seal and possibly impeller, and rewiring.

Am I correct that I can use a 2 speed motor, even though my current motor is single speed? I can't see how any of the parts in the pump head would need to be different, and pentair offers a dual-speed model with the same "wet parts".

One more question regarding pump HP sizing: I have a polaris 360 that connects to the pressure cleaner line, powered by my current 1 1/2 hp. Will the 3/4 HP pump have enough oomph to drive it?

I am SO looking forward to getting all this sorted out so we can SWIM!
 
Hmmm, good thought on the 360. I've had two suctionside cleaners and they both have been finicky about pressure and volume. That could be an issue if you downgrade the pump. You can always restrict flow but never increase beyond the pumps capacity. That a question I'd pose to the Polaris folks or someonw here who has one.

BTW, what's keeping you from swimming? How does your water look?

PS - Thanks for the kind words on the kit. It's rewarding to watch a kit order go out and the see test results posted on the forum a few days later.
 
BTW, what's keeping you from swimming? How does your water look?
Click to expand...

At the moment it looks fine, because I drained 1/2 & am refilling. CYA levels were crazy high, I think because the previous owner (we've been in the house about 2 weeks) used large amounts of trichlor tablets to deal with the broken/failing filter. When we moved in, there was a good bit of mustard algae on the bottom & sides - the pool sat unmaintained for about 2 weeks. I brushed & shocked it, and was cleaning the filter when I discovered that it was broken. Believe me, as soon as that baby's full, I'm in the water.

I talked to Pentair tech support and some of their answers didn't quite ring true. The tech claims you can't downsize more than 1/2 HP, even though almost all of the pump parts are interchangeable across their whole line of 3/4 - 2 HP whisperflo's. When I asked why, he said they didn't cover that in the training, only that you couldn't go down more than 1/2 HP - I'm not buying it - if you look at the replacement parts diagram in the pump manual - the ONLY different parts across the HP range are impeller & motor, and the diffuser assembly which is the same for .5 - 2HP and different for 3HP.

The tech also said that a Tagelus TA40D filter would be a good match for my pool & pump - this thing has a flow rate of 40GPM and the suggested pump size is 1/2 - 3/4 HP...

I think I'm going to try come up with a more accurate estimate of my head - that seems to be the sloppiest piece of my guesswork.

The plot thickens...
I noticed in the pump manual that the HP rating on the impeller for my pump (WF-26) is 1, not 1 1/2. Perhaps this is an "uprated" pump? If so, then I've been looking at the wrong pump curves. 1HP w/ 50 ft head = 90GPM and w/ 60 ft = ~76 GPM - which is close enough to the 62 GPM filter rating that I may not need a new pump/motor.
 

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It sure sounds to me like you've got a grip on the issue.

Calculating TDH (head) is likely to drive you a little crazy. Mas985 is the guru and he'll probably see this or you can PM him. For your purposes, you'll probably be fine with the "guesstimate" approach.....anything more detailed is w-a-a-y out of my pay grade.
 
Hello Julian,

Did you come to a resolution? I appreciate your in depth study of the situation and possible remedies.

The typical differences between a top mount and a side mount on filters are their design characteristics. Side mounts are typically all designed for high flow applications with an external valve.

Is there a dedicated return for your 360?
 
I found a 24" Hayward S244T on e-bay for $235.

I'm sticking with the current pump for now.

I do have a dedicated return for the 360. This, combined with the HP stuff I've noticed in the manual that leads me to believe I may have an uprated 1HP pump, means the pump & filter are more closely matched than I thought (I think).

Other (good) news is that my homebrew fix to the current cartridge filter appeared to work, so the water's in decent shape, until the new filter is delivered. Thanks to some very helpful folks here, I'm confident I'll be able to do the hookup myself.

Once it's up and running, assuming the pressure in the filter looks reasonable, I'll leave it alone and pour a margarita.
 
TFPJules111,

Nice homework on your part discovering that your pump impellor puts a load of 1 brake horsepower on the motor.

Only an engineer would be crazy enough to delve into pump curves (I are (sic) one also), so I'm assuming you realize that it doesn't matter whether the motor is rated for 1 HP or 1.5 HP. If the motor only "sees" a brake horsepower load of 1 HP from the impellor, then that is all the horsepower that the motor will draw. Similarly, a load of 1 brake horsepower on a 5 HP motor will still draw only 1 HP of load from the 5 HP motor.

I'm looking forward to seeing pictures of your pool and your new equipment.

Titanium
 
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