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Thread: DE Filter questions: "blowthrough" and normal pressure?

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    DE Filter questions: "blowthrough" and normal pressure?

    Hi,
    Unfortunately I can't get the search feature to work - not sure if I'm inept or if it's broke...

    I've got an inground pool with a Hayward DE filter that I had a couple of questions about. Filter is 36 square feet, three 1-1/2" return lines (one about 20 feet, one about 30, one about 45 that gets no traffic), 1 HP pump, all about 6 years old.

    -Is it normal for there to be some DE "blowthrough" when I charge up the filter? I generally mix the DE in a 5-gallon pail of water, and pour that slowly into the skimmer. When I do that, there's a pretty big plume of DE that gets dumped back into the pool. Eventually it gets picked up by the cleaner, but it sometimes takes a while. There are no obvious cracks/tears on the filter innards, but I haven't done a complete tear-down and inspection yet.

    -Is there a "normal" pressure reading for this type of DE filter? After cleaning but before the DE goes in it's running about 20psi, and that doesn't change much when the DE goes in. (Of course, if all of the DE is being blown back into the pool, that may be why...)

    Thanks,
    -Mike

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    JasonLion's Avatar
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    There isn't a "normal" filter pressure. It depends on many details of your plumbing and is different for almost every pool.

    It sounds like you have a tear in one of your grids/fingers. DE should not be getting through. If it seals up quickly after adding DE then it is probably a very small hole, or several, and not easily visible.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    duraleigh's Avatar
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    Hey, Mike,

    I'm not a DE specialist butI know it should not be blowing back in your pool....that requires investigation.

    It also seems like your pressure should rise a little when you charge it with DE so I suspect you are losing quite a bit thru some mechanical problem in the filter.

    Other DE folks will be along soon and shed more light on the problem.

    BTW, welcome to the forum!!
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    I never see DE going back into the pool. You have a breach inside your filter. Time to find the source of the leak.

    20 PSI is high when compared to my filter, but I suppose it depends on pump size vs. filter size. I have a 60 sf DE filter with a 2.5 HP high head pump. I have about 13 PSI after backwashing and about 14 PSI after I load the fresh DE. I generally backwash and reload at around 20-22 PSI as the water flow is visibly reduced as the back pressure rises.

    OT - I'm an ex-Digital employee from way back. Used to live in Marlborough and Worcester in the 80's. I sure don't miss the winters in your part of the world!
    26,000 Gallon Gunnite IGP
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    A small amount of DE blow back on recharge seems to be normal. At least it has done that on both my DE filters. You need to tear down the filter and remove the grids to look for tears. I found mine to be on all the hard edges of the grids along the bottom edge. I had a top mount manifold. They can be fairly subtle. Also check for broken tubes that hold the grids to the manifold. Both were problems I encountered.
    30,000 gal Pebble Tec, Intellifo 4X160, Pentair 80 DE Quad, Pool Pilot SWG, Easy Touch Controls

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    Thanks for the advice...

    I ripped the filter apart, and one of the elements is broken where it fits into the manifold. Doesn't seem like a big enough crack to cause the problems I'm seeing, but I can't find anything else wrong so I'm hoping that's the problem.

    Harry, the winter around here makes the spring that much nicer. Lived in San Jose for a couple of years, and with the constantly good weather, it just meant that people complained if it was only 70, or if there was a little wind and clouds on a Saturday. It was nice to be able to easily plan outdoor events, but too much nice weather just makes your "bad weather" threshold lower...

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    I doubt it takes very much to cause the blow back. At first glance my grids looked good but there were tears right along the bottom edge that you did not see until you moved the fabric one way or the other. Regardless, any void is an avenue for the DE to go back to the pool. But I believe you will get some normal blow back on a recharge until the grids get coated.
    30,000 gal Pebble Tec, Intellifo 4X160, Pentair 80 DE Quad, Pool Pilot SWG, Easy Touch Controls

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    One problem down, at least one to go...

    So I received the new filter grids yesterday and installed them. The good news is that with the pool cleaner sucking the silt off of the bottom of the pool, there was no visible "blowthrough". The bad news is that it seemed to work fine for a little while and now I'm having some sort of pump/filter problem that I don't quite understand...

    With the new grids installed but not charged up with DE, the pressure gauge on the filter is reading 20psi (the same as with the old grids). I decided to try cleaning the pool (with a kreepy krauley) without adding any additional DE, based on the fact that the silt is probably 50% DE in the first place.

    With either the skimmer/KK or main drain open, the pump appears to be working properly, and the filter pressure reads 20psi. However, within a few minutes, the pressure gets up to about 27psi, and the KK stops moving. When I backflush, however, the water that comes out is clear. I put it back into filter mode, the pressure reads 20psi again, everything seems to work fine for a while, then the same thing happens.

    I know that I've got some problems with the filter valve (new one should be delivered today), however I can't exactly figure any way that the valve would be causing the problem. The return lines (3 x 1-1/2") all appear to be working fine as well.

    Any ideas?

    TIA,
    -Mike

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    Actually, I may have just figured something out...

    The filter valve is designed with 2" inputs, as is the heat pump (and probably the chlorinator). I don't remember if the pump input is stepped down to 1-1/2" or if that's as big as it can be. Everything between the ball valves for the main drain/skimmer and the return line manifold is piped as 1-1/2", with reducers at each "fixture". I'm no expert (I didn't do so well in 2.20), but it seems that restricting the system to 1-1/2" (down from 2 x 1-1/2 on the input side and 3 x 1-1/2" on the return side) is pointless.

    Since I need to cut and replace a bunch of the piping when I replace the valve (nope, no unions used on this job...) is there any reason not to bump it all up to 2"? I believe the only part not readily available at Lowe's is the backflow preventer before the heat pump, which I know could stand to be replaced...

    The guys who installed the pool were idiots; there's not much value in detailing the things which they did incorrectly, but when they started the install I trusted that they had an appropriate filter system design, and in retrospect I have no reason to believe that was the case.

    All of the drain and return lines are 1-1/2" flexible PVC, with 1-1/2" rigid PVC above ground at the filter. The pool has a main drain and one skimmer (probably 45 feet and 25 feet to the pump), and three return lines (runs of approximately 20 , 40, and 45 feet). In order, I've got a 1HP Hayward superpump, a 36 square foot Hayward DE filter, an Aquatemp heat pump, and a Hayward in-line chlorinator.

    Thanks,
    -Mike

  10. Back To Top    #10
    How old is your gauge ? Are you sure it's accurate? My 48sf DE filter with a 1 hp pump runs about 10psi charged and I backwash at 14-15psi... 20+ would scare me.
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    JasonLion's Avatar
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    If you are vacuuming up heavy silt a DE filter can clog up very quickly. Running a DE filter without DE can clog the grids in a way that backwashing won't clean out. You may need to take the grids out and clean them.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Quote Originally Posted by Phillbo
    How old is your gauge ? Are you sure it's accurate? My 48sf DE filter with a 1 hp pump runs about 10psi charged and I backwash at 14-15psi... 20+ would scare me.
    I've replaced the gauge, so I'm relatively confident that it is accurate. When I was standing next to the filter when I turned it on the other day, there was a significant swelling of the top of the filter housing as it became pressurized (it seemed like at least 1/2" of vertical height), definitely more than seemed safe. When I saw it, it pretty much scared the junk off of me...

    I just found another problem with the Hayward in-line chlorinator. I've had various problems with the flow through it (as opposed to "past" it) since it was installed. It comes assembled with a 3/8" plastic hose from the base to a lower port on the housing (1/3 up the housing), and two years ago I moved the line to the upper port (top of the column) because I stopped getting adequate chlorination. Last year I removed the valve which regulates the flow through that tube, because even at "full open" it was letting through only a trickle, much less than had been going through in the past. I just disconnected the line with the filter running and at 25psi, and there was barely a trickle, and with no legitimate pressure. My guess is that the other end of that hose is somehow clogged.

    However, it also points to a flow obstruction up-stream from the chlorinator; if the cause of the 27psi were downstream, I would expect much more pressure at the chlorinator. My guess is that the check valve is causing more of a problem than I first thought...

    I'm off to replace the filter valve, check valve, and all of the piping in between the pump and the return lines with 2" - I'll let you know what happens...

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