Pump/Filter Sizing Mytery

[kingbud]

We bought a place with a gunnite or concrete pool 20 x 40 x 12’ deep, knowing that we were going to have to work on it. 45,000 gallons. Call it Lake Woebegon. The 1.5 hp pump is shot, it cavitates, it leaks, it is loud. The DE filter is also shot – amazingly, it is a 36 square foot Sta-Rite unit which I discovered at startup had two grid ports permanently plugged, reducing capacity by something like 15%. When you pick the grid assembly up it tinkles like Christmas ornaments, there is so much broken plastic rattling around. No kidding. And the grid’s fabric is punctured in quite a few places. Another delightful surprise we found is that the main drain is plugged with screw-in plugs. To recapitulate: the pool in its present state is being serviced by a severely crippled filter, an oversized pump that is slamming it with air, and one 1-1/2” suction line coming from the skimmer. By the way, there are three return lines, two at each end opposite the skimmer (which is located near the corner of the deep end), and one on the same side as the skimmer in the shallow end.

Those who have read my other recent posts might recall my tale of a massive algae bloom, which with patience and a lot of chlorine we managed to kill off. Well, here’s the kicker: the existing filter/motor setup cleared up the water after the bloom, if not overnight then over two nights. The water is crystal clear.

What am I not getting here? A quick glance at filter sizing charts recommends 72 square feet, a 2 hp motor, and three 2” suctions for 45K gallons. How is my crazy system doing such a good job of clearing the water? Is this a testament to the intrinsic superiority of the DE filtering concept?

Another question: assuming that I can get the main drain opened up and repair or replace the broken sections of plastic pipe, thus giving us two 1-1/2” suction lines, then what minimum filter/motor combination can I “reasonably” get by with when I go to buy new equipment? (I must confess, I am squeamish about punching holes in the pool walls to add suction lines.) Incidentally, I am seriously thinking about converting to a vinyl liner – one big advantage (I assume) would be that I can fill the bottom 4 feet of the deep end with sand and shrink the pool volume to roughly 36K gallons.

Talk about your fun in the sun!!

Let me say this, I am grateful for having the support of the many kind and knowledgeable people that participate in this forum. Where would we be without the internet?

[Vinyl_Guy]

Well you've got your hands full..

How much do you run your system? I've seen inadequate pumps and filters keep pools crystal, but they ran up quite the electric bill. .

I know I'm not much help in this area, but I bet some one here will crunch the numbers. With a single 1-1/2" suction line a 2hp pump is a waste, but if your planning on doing some major overhauls then you'll have to plan for that. 72sqft sounds like overkill to me, a nice Nautilus at 48 should do the trick, don't you think? Or one of those new amazing cartridge filters. I was putting a lot of them in towards the end of my pool days (4 years ago). I didn't do much spec on the pools I built the salesmen and owners always did that. I just built the darn things.

Here's a thought though. Have you considered just converting one of the 3 returns to a "side wall" suction? Rather the trying to fix the main drain? Which tends to be costly and sometimes impossible. Or coring through the wall (not fun either). If you had 1 suction and 2 returns it's just robbing Peter to pay Paul. But with 1 suction and 3 returns, the numbers might work a lot more efficiently with a set up of 2 and 2. And the line already exists.

Is your pool free form, or is it fairly symmetrical with some good straight lines and well defined corners and angles?

I've done a couple vinyl conversions though. They're not fun and if the pool isn't totally uniform I suggest having the liner company measure it also. It costs extra but sometimes they will guarantee the fit when they do. I did a concrete wedge pool conversion once. Shear walls from top to bottom (deep end too). It looked like a car ramp turned upside down. The steps were free form and I had to supply cardboard templates of the treads (tops). I also had to take plumb bob measurements to make sure areas of the bottom didn't bulge too much. It was 8hrs just to measure the damn thing.Then tapconning the extrusion into the wall, was a ball breaker. Needed pipe staging for the deep end. Fit beautiful and the owner loved it. I believe we spray tacked foam on 100% of the pool, if I remember correctly. The liner company couldn't or wouldn't guarantee the liner with out some buffer in between , because of the roughness of the concrete. The only other option would have been to diamond grind the whole bottom and walls.

Just tossing some thoughts out there.

[kingbud]

hmmm... well first, thanks for weighing in. (They don't offer a Smiley icon with a furrowed brow, do they?)

Yeah, I think 48 should be plenty with the properly sized pump. I hadn't thought about cartridge filters, I will check into that. I have had tunnel vision about DE since that is what I had in my old place, and it did such a good job... I have since learned that my old system was oversized for the pool, I guess that had a lot to do with it. I'm gonna investigate sand as well, since I've learned in this forum that you can enhance with DE.

I never thought about converting a jet to a suction, I think that is a great idea! Thanks! I think the one diagonally across from the skimmer would give the best circulation.

On the subject of vinyl... you gave me a lot of food for thought regarding fit that I hadn't recognized. I had realized how much work would be involved to tapcon or otherwise anchor some kind of rail or hanger for the liner - scaffolding or some kind of bosun chair would definitely be necessary - but there are other problems. Even though the pool is rectangular, there are steps to contend with; there is also about a 8 - 10" shelf that runs all around the pool at the elevation of the shallow end, or 42"+/- below the deck. It is kind of a cool detail, but now I don't know how you could put in a liner that would accomodate that, unless the liner terminated where the bottom starts its slope toward the deep end, leaving the shallow end un-lined... maybe that would work. Another consideration is that the walls have a slight taper going down, maybe 3 or 4 inches in the deep end.

Of course if I did manage to deal with all these issues, then in my scheme to "shrink" the pool by partially filling the deep end I would have to figure out a way to extend the main drain up to the new floor, assuming I could get it opened up and working (one advantage of my day gig is I have free access to master plumbers... )

sigh... I guess I'll just have to deal with the water bill and go ahead and fix the cracks in the concrete - I think I can do that myself. I would grind them out to a uniform width and then -- caulk or grout them back. Would you mind giving your opinion on which method would be better?

Hey man, thanks a lot for your time!


PS: What I meant by "shelf" was that I have vertical side wall 42" tall, then the pool wall cuts in 10 - 12", and then it drops, slightly tapered, to the bottom. So the measurement at the top would be 20' across, and then 42" down, it would measure a little over 18' across. Incidentally the top side walls appear to be some kind of plastic or fiberglass panel with caulked (leaking) seams, and lovely blue patterned glazed tiles topping it off, with a central 4" main tile and 2" border tiles top and bottom. It's really pretty, although it's missing one section and it looks like somebody with a tooth knocked out... I don't know how the top side panels mount or tie in on their bottom edge.... yet

[Vinyl_Guy]

No problem KB,

I know how you feel, it's hard to translate this type of thing into words that make sense.

The "shelf" is generically called a safety ledge. At some point designers had an idea that if some one fell in the deep end (that couldn't swim), the ledge would give them the ability to "stand", and orientate themselves.

What happened more often was, adventurous children used it for venturing out from the shallow end, using it like a sort of cat walk. They ended up being more trouble then they were worth.

Vinyl comes in rolls that contain a wall pattern, tile at the top, and a pattern below it, in several common wall heights. 42", 40" and so on. What happens when there is a safety ledge (shelf), is the additional volume of the the triangle that makes up this area is added to the calculation of what the deep end would be with out it. They figure out the bottom as if it wasn't there, then add extra liner, minus a bit for a tight fit. That's the simple version of how they do it. The ever decreasing deep end angles is all done on CAD machines, and some how they add the volume of the this shelf into the those numbers. The CAD program spits out a sort of parts list of triangles and other shapes. It's all cut out of vinyl of the the "floor pattern" you've chosen and "seamed" together. It's actually more like a triple stitched weld since the vinyl actually melts a bit. It's done with low intensity lasers.

As far as the main drain goes. If (and that's a big if), it can be repaired, theoretically hammering it out to the point where you can attach a pipe to it and extend it through the added sand is not an impossibility. I've done a few like that, but it was during builds in which the original dig was too far into a water table and the pool had to be "shortened". Also this entire process would have to be done before the liner is measured by any outside parties. Allowing for the variations in how it might be done would be far too complicated.

The liner can't really stop at the deep end or terminate anywhere underneath the water for that matter. Unless something has been specifically designed to receive it that way. At one point in history a pool was created opposite of how you describe. With a liner in the deep and shallow ends but terminating about 6" up the wall. The wall was designed with a water proof "track" to receive a normal liner in it. The theory being that most liners fail above the waterline due to UV and chemicals accumulating on the surface of the water. I believe the company was named Polynesian or something to that effect. They were a miserable failure and plagued with problems. It was a short lived design. I've only seen two, one is still hanging in there, as I said plagued with problems. The other was torn out completely and the hole was reused for a new pool.

Liners were intended to "line" the pool's entire volume of water, that's how they work best, IMO anyway .

A liner can be measured to fit the "shelf" and your steps, and just about anything. How well, and with how few or no wrinkles is the question. A liner company might guarantee the fit if they themselves measure it, but it costs to have a team of them come onto the site and do that. They might not even guarantee it if the pool is far too irregular.

Tapconning or whatever method you use to attach the extrusion (track), is another story. With a rigid metal track there's more strength to it, and they require less fasteners. With something more durable with the water a plastic for example, they need them every 6". The track is usually the same as any other one for a vinyl liner. But it's only the slot itself and no coping or decorative edging to finish it off, or receive a concrete deck. It's basically a rail with the extrusion as part of it. Except it's mounted vertically (the slot) and the liner goes up and over the forward edge of the rail, and then down and into the "slot" itself. The few I've done were "spec'd" out this way by the vinyl people. I think it allows for the rail itself to be more narrow as it now would not have to accommodate the size of the liner bead horizontally. A wider or thicker rail with the liner bead inserted horizontally would have a lot of down force or pull on it. In close and tight to the wall or "thin" is better when exterting downward forces.

Whether the pool is gunite or concrete makes a difference too. Gunite is not really all that substantial of an material to drill into. Since it has no aggregate (stone in the case of concrete), it's more like mortar or grout when drilling into it. Gunite tends to deteriorate from drilling and holds fasterns not nearly as well as concrete. Plus if it's gunite there's a layer of plaster that dulls drill heads quickly since most pool plaster contains a an element of marble dust as part of its make up.

I've not done a lot of gunite or concrete work and sealing anything like cracks in either of these materials is a whole nother discipline. The times I have done it, a "V" groove is carved out of the crack itself to widen it. Then a water proofing like mortar is added. Thorite or some kind of water plug. Caulking below the water is rarely used since it always remains "gummy" after water is added. I suppose a two part deck sealing epoxy might do the job, but I don't know about it be submersed for long periods. And if the cracks are on anything other then a flat surface deck sealing products don't work well, they are very "runny". Unless your referring to cracks in the deck, then disregard this last part .

If any of this doesn't' make sense.......I'm not surprised. Something always gets lost in the translation when things get this complicated.

[kingbud]

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wow, dude, you are really generous with your time!! thanks. I'll be back later... processing... processing... processing...

[Vinyl_Guy]

Thanks

My time is sort of relative at the moment.

I'm unemployed (as of now) and I type like the wind.

It's good for me to stay busy and feel useful .