Upgrade recommendations for replacing 14" Intex sand filter combo?

My thinking was that since Hayward pairs the 18" filter with the single speed 1 HP pump and a 1.5 HP 2 speed pump as complete systems - I couldn't be going too far wrong with a 1 HP 2 speed pump. If it needs throttled to backwash on high without flushing sand out - so be it. The only way I see this is a bad deal is if the pump doesn't provide enough circulation on low, and I don't think that's likely. As far as the valves go, I hadn't realized one was "pool rated" and the other "industrial".

I just realized the S210T 21" filter is only about $35 more than the 18". Hmmmmm?? More thinking. The flow rate for the 21" is 44 GPM at 20 GPM/sq.ft and 27 GPM at 12 GPM/sq.ft. And I saw somewhere that the 1 HP 2 speed pump puts out about 40 GPM @ 25' of head - on low. Is the profit margin really that much higher on motors than filters? Or do the filter people think they'll sell more other stuff if they sell you a terribly mismatched system?

What the sales people know is that HORSEPOWER sells, and filter INCHES do not. I've never seen any evidence that they care enough about anything else to even learn how negatively excess pump size affects pool operation!

It's the same mentality that produced ads associating Marlboro cigarettes with sexy independent toughness, rather than with black and leathery lungs that are prone to cancer, long after EVERYONE knew that that the 2nd association was the true one.

I found a Hayward pump/filter sizing .pdf that tells how to calculate which pump and filter you need. Based on that document, with a 21" filter, I need a pump that produces between 12 and 44 GPM @ 30' head. According to your suggestion of 12 GPM/sqft - 27 GPM would be the max flow. What would be the minimum flow required to adequately backwash a 21" sand filter - the Hayward S210T in particular?

15 GPM / sft is accepted. It's what I've designed for on large commercial rehab projects, and always seemed to work OK.

Generally, a centrifugal pump that will deliver 12 GPM through a filter and return piping is -- under most conditions (obligatory 'weasel' words) -- likely to deliver 15 GPM in a full open backwash.

Doesn't that work out to 36 GPM for a 21" filter - to backwash? And 27 GPM or less to filter? I guestimate that I have about 30' total head restriction in my system. The flow curves in this brochure

https://hayward-pool-assets.com/asse...f?fromCDN=true

Show that the SP1750 1/2 hp pump is making about 35 GPM at 30'. That pump might still need throttled to get down to 27 GPM on my system. It also shows that this pump makes about 40 GPM at 25'. Almost exactly what I read the 1 hp pump makes on low. Is 27 GPM enough flow for a manual vacuum head to be effective? I'm certain the 18" filter is plenty big enough for my pool, but it looks like there is no pump small enough to properly operate that filter. It looks like even the 21" filter needs to be throttled on my system - because there is so little piping restriction - to get down to a 12 GPM/sqft flow rate. A one half hp pump would be fine and dandy for a 21" above ground filter system, and Hayward is marketing a 1.5 hp 18" system. Makes me shake my head in confusion.

You have to look at the flow/head tables. 1/2 HP vs 1.5 HP doesn't necessarily mean ANYTHING, because of all the games they play with horsepower ratings.

One of the things I've dreamed about, is setting up a pair 'Consumer Reports' type test pools, to test various pumps, valves and filters and then publishing the results. Doing so would provide objective data about that equipment that is not currently available.

Well, one thing is for sure - I now know more than I thought I wanted to about pool filter systems. I can't find much (in some cases - any) flow/head info on AGP pool pumps. I emailed Hayward and asked for that information specifically about the 1 hp 2 speed PowerFlo Matrix. We'll see where that leads.

At this point, I'm planning on the S210T Pro Series filter and the SP15922S PowerFlo Matrix pump. If I was sure I could still vacuum effectively (with a manual vacum), I'd strongly consider the SP1750 1/2 hp pump. We are leaving for a few days of vacation this month and I'm going to wait till we get back to order.

I think the system above will clean my pool in about half the time it takes my current system. If I throttle the pump so there's no sand washed out on high, then only use high for backwash and vacuum, this system ought to be a good one. My 14" filter has about 1.06 sq.ft of filter area, the S201T has more than double that. I think I'll be running about the same GPM - if you believe Intex propaganda. I know the Intex system I have blows stuff through the sand.

Am I kidding my self?

Power-Flow II flow / head ratings, including SP1750

https://i.imgur.com/iM37D6h.jpg

Also from https://www.hayward-pool.com/shop/en...ii-a-pppow2--1
https://i.imgur.com/yLGqTez.jpg

BTW, the KW rating in the first image is nominal, not actual. I can't find actual amps at load for this pump ANYWHERE.

Thanks! Now if I could just get the same info - including low speed - for the PowerFlo SP15922S. I suspect the "Power-Flow II" and "PowerFlo Matrix" tables and charts all have very similar numbers, but I don't know that.

I'm worried that the SP1750, when the vacuum hose and vacuum head are attached, will not have enough flow to vacuum the pool floor. I don't know how much additional head the vacuum adds and I don't know how much flow is needed for vacuuming. I have this head

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If the SP15922S on low has performance similar to the SP1750, and it won't vacuum on low, I can turn it on high, then throttle the flow as necessary.