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Fix for leaking EC-75 filter (hairline crack)

Severe leak in EC75. Pool store offers only option: 'buy a new filter and we will install it for you'. Water running down side of tank in flat stream about 6 inches wide -- actual gush of water when pump starts up -- sometimes pencil-lead thick stream coming out from under the top-part. Can hear air sucking in when pump is not running, but stops after while -- pump does not lose prime and water does not seem to be draining back into pool thru intake. Leaking about 650 gallons each day. Here is how I fixed it.
Took top off, drained tank and dried it. Felt around top edge and found what could be a crooked hairline-crack, entirely above the 'ridges' on the inside of tank. The crack meandered and was entirely above that side of the tank where I had seen water running down the outside of the tank during operation. The crack is barely visible to the eye but is obvious to the fingers. At first I thought it was a thread of silicone caulk but decided it was a crack when it did not rub off.

Made sure outside of tank was dry all around, filled tank with water (no pressure) to above the suspected crack. Grabbed the sides and squeezed -and-pulled hard, once, trying to emulate the tank's flexure under pressure; the squeeze-and-pull may not have made any difference, but sure enough, water was coming through the side of the tank & draining down the side. Emptied the tank and dried it outside and inside to below the crack.

Cut a patch from pool-vinyl. Made it wide enough to extend down inside the tank (only) and below one or two of the 'ridges' and long enough to extend about an inch (2.5cm) past each end of the crack -- SEE NOTE-- but if I have to do it again I will probably cut it narrower so it will not cover any ridge.

I used "Sticky Jack Glue" that I got from Starcrest and had used to fix a rain-barrel problem. Dried the area that would be patched and spread the glue evenly (?) on it and beyond the ends of the area being patched. I think I used too much glue. Dampened the vinyl patch and applied it, pressing it into place. Did not walk away and leave it.

The glue foams up a little as it cures, which I know Gorilla Glue also does, so maybe Gorilla Glue could do this just as well (better?)..

Checked it after a few minutes and the patch had started sliding down the inside of the tank. I think this was partly because I used too much glue -- the glue is a little viscous and thus 'lubricates" the area until it sets up a little -- and partly because I had cut the patch a little wide and it was sliding down over the top ridge and so was being 'lifted' a bit instead of being impeded by the ridge. The patch had also lifted in 2 places along its length because, after all, it is a flat piece of pool-vinyl (about 1.5" x 9") and the surface I am gluing it to is concave, so it fits unevenly -- this "lifting" or "wrinkling" might have been avoided (?) if I had I stretched the vinyl before applying the patch.

Got some C-clamps and VERY LIGHTLY applied them to hold the patch in place until the glue set up a little. Not tight at all or it wrinkled worse. I did not use clothes pins because I thought they would be too tight a grip.

Checked it after a few more minutes and smoothed out the places where it was still wrinkling and trying to lift. Rolled up a piece of thin cardboard (a political-campaign postcard) and cut an inch-wide chunk off its end, then loosened a clamp and slid it under the clamp and closed the clamp just enough to hold it -- my idea was to spread the clamping force over a wider area and get the advantage of that little roll-of-cardboard's springiness so as to keep a very light pressure over that area.

Checked it about an hour later and everything looks copacetic.
DAY TWO: Removed the C-clamps and put the top on, tightening the bolts in a sequence that spreads the pressure as evenly as possible -- as always -- then started the pump and provided DE.
Pressure is nice and low. No leak. No, wait; there IS still a leak. But not the spurt, sheet, or steady stream like it was. In fact, it makes me think of a cold pitcher of iced tea that I took out of the fridge and put on the patio table -- except it is less than that, and only in one place, not across the whole 6 inches like before. It is so little, and so slow -- I recall that the glue looks like it has a cellular stucture, once dried -- and such slow leakage must have a microscopic pathway -- I recall that I bump the pump because the pressure goes up as DE clogs the internal "fingers" -- and it seems reasonable that maybe the DE will be able to clog this leak. Ran the pump the usual 12 hours (I am in Central Florida: long days and hi temps).
The "sweat leak" is gone. The pump is running fine, the pool looks good, the pressure is low.
Still no leak, pump runs fine, pool looks good, filter-pressure is still low. This looks like it is working.
*NOTE: The classic way to stop a crack from spreading is to drill a small hole at each end of the crack. I forgot to do that -- and I HAVE a 1/64" bit .-- since I did not to this to relieve or spread the strain I should not be surprised if, over time, the crack spreads beyond the edge of my patch. As it turns out, since the patch is holding, I can hope that the effect of the glue-&-vinyl will also impede the strain and maybe reduce it somewhat. However, if I do have to try another fix I think next time I will probably do a compression-patch -- I have seen that on some pressure vessels (low pressure ones) and would expect it to work here. I would probably have to make it of stainless steel and use stainless bolts, washers, and nuts -- probably about $10 worth. My vinyl patch cost less that a buck.
ANOTHER NOTE: Maybe if I had thought more I would have doubled or tripled the thicknesses of pool-vinyl I used, because I now realize that the DE swirling inside the filter will erode the vinyl and expose the underlying cured glue and must eventually expose the crack again. Well, for however long the erosion takes it is money not yet spent. And perhaps the DE will 'mat' on the patch-assembly as it does on the fingers, and thus prevent the erosion and maintain the function.

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