Upgrade recommendations for replacing 14" Intex sand filter combo?

[PoolDoc]

My experience has been that the Hayward pool valves are lower grade than the Hayward industrial valves.

Will this make a practical difference to you? Dunno. What's going to matter is whether you can operate the valve. Larger ball valves can be 'stiff'. That's why I suggested the S-80 nipple as the attachment point, so you will have a firm strong connection to stand the torque of handle operation.

One caution: AG filter "design flow" is bogus, and has been for years. Sand filter 'efficiency' at particle removal INCREASES as flow rates DECREASE. Inground pools are rated at 15 GPM per sft of sand filter area. Above ground pools are rated at 20 gpm. An 18" filter is rated at 26 GPM for an in-ground pool, but up to 35 for an above-ground pool. The lower rating on that filter is possibly that it has a shallower sand bed, which lowers the rating. Unfortunately, for good filtration you need to run at 12 gpm/sft, or 22 gpm.

Why the difference? Just because . . . of marketing needs. There's no science or engineering behind it; filtration requirements on AG pools are actually MORE demanding than on IG pools.

So, do what you like. But 58 gpm is more than TWICE the optimal flow through that filter. Low speed probably won't be enough to backwash, but on high, you'll likely lose sand every time. And if you ever turn it on 'high' when it's set to filter . . . you'll clean the sand right into the pool!

[Pappy]

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".

[Pappy]

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?

[PoolDoc]

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.

[Pappy]

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?

[PoolDoc]

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.

[Pappy]

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.