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Thread: Oscillating water

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    Oscillating water

    Hello: This morning about 30 minutes after turning on the pump and filter, I developed this huge oscillation. My daughter spotted it and said "Dad, we have a tidal pool." The water would bulge up, direct center, actually going higher than the edges of the pool, then fall, with water splashing over the sides, then repeat. It was strong/violent enough that if we had not noticed, I think the whole assembly would have easily torn itself apart.

    Pool is above ground, 6,000 gallon round intex. A bought a 1.5HP pump and cartridge filter--it's strong, and more than enough for the pool, I'm told--maybe too much?

    Question is, is it possible to dampen this? And not sure why it only happened now, when everything's been fine since I set it up about a week ago...

    One more detail, the location of the input line is near the top water line. So the pump pushes water in and away, then the water rushes back in, then gets pushed away again--I guess this is what starts the oscillation.

    It's quite a sight, with that huge bulge rising and falling. I'm sure it would be fun to swim in--but I'm also sure the forces being generated will soon result in disaster!

    Any ideas???

    Thanks

  2. Back To Top    #2
    Mod Squad JohnT's Avatar
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    Re: Oscillating water

    Just as a point of reference, my 21,000 gallon inground pool uses a 1HP pump which is more than sufficient. You are way oversized for your pool.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
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    Re: Oscillating water

    Quote Originally Posted by JohnT
    Just as a point of reference, my 21,000 gallon inground pool uses a 1HP pump which is more than sufficient. You are way oversized for your pool.
    Thanks. I was afraid of that... Any downside--other than the current one, and wasted $ on the purchase--for being oversized with the pump?? I guess it eventually might tear the liner, near the intake and outlet ports...

    Regards

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    UnderWaterVanya's Avatar
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    Re: Oscillating water

    Can you add something to the return and maybe get it lower in the water? A 90 degree elbow down and then an eyeball? That should stop the surges.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Oscillating water

    Quote Originally Posted by UnderWaterVanya
    Can you add something to the return and maybe get it lower in the water? A 90 degree elbow down and then an eyeball? That should stop the surges.
    Good idea, thanks, I'll try that. As usual, the proprietary/non-standard/downright funky nature of the intex parts makes it difficult to fashion something from the standard parts at pool supply or big box stores...

    When I add something to make the return lower, is there a preferred place--e.g. near the bottom of the pool, middle, top? And for that matter, should I lower the suction side as well? Any 'rule' about where the ins and outs should be, and whether one should above/below the other??

    Thanks again.

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    cramar's Avatar
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    Re: Oscillating water

    I could be wrong but I can't see you dampening the pressure with a couple of elbows, I have a 1hp pump for my pool, I hard plumbed some solar panels on my roof and it was a pretty good run of pipe with alot of joins, didn't do all that much to drop the pressure.

    Maybe buy a new one and try to sell the old?
    20' X 54" Sharkline Matrix Resin AGP, 9400 Gallons, Sta-Rite 1 HP Dynamo Pump, 150 lb Pentair Sand Filter, Gorilla Pad,
    Foam Cove, Taylor K-2006 kit, BBB method, 8'X20' Fafco Sunsaver Hard Plumb, DIY Fountain, Margarittaville Fiji


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    UnderWaterVanya's Avatar
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    Re: Oscillating water

    Quote Originally Posted by cramar
    I could be wrong but I can't see you dampening the pressure with a couple of elbows, I have a 1hp pump for my pool, I hard plumbed some solar panels on my roof and it was a pretty good run of pipe with alot of joins, didn't do all that much to drop the pressure.

    Maybe buy a new one and try to sell the old?
    My point wasn't that the pressure would go down - the surges he's seeing seem to involve the return pushing the water so hard that the water level drops below the return - which then rushes back in and creates some standing waves. By putting the return lower - I figured he could get out of the cycle and create some circular rotation which isn't a bad thing.

    Ultimately he might have to do exactly what you suggest - but it seemed worth a quick try. My impression is that his filter is sized for this pump which would mean he may also need to change filters if he downsizes the pump.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Oscillating water

    I try to make the water circle around to the skimmer so I try and point the eye to the left and down usually, (can aim it up if you need to aeration). Not sure if this is correct or not but my skimmer has been collecting everything from the surface and most of the bottom debris seems to collect in a single spot in the middle.
    6500 gal, Intex 18'x48" above ground, 1hp Pro Sand Filter, TF100 Test Kit

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    UnderWaterVanya's Avatar
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    Re: Oscillating water

    Quote Originally Posted by jnealhicks
    When I add something to make the return lower, is there a preferred place--e.g. near the bottom of the pool, middle, top? And for that matter, should I lower the suction side as well? Any 'rule' about where the ins and outs should be, and whether one should above/below the other??
    Unless you are having problems with the suction side I wouldn't change it. As for the return - just take it down a little and turn it so it points along the wall rather than out - that will create a circular flow.

    How much suction do you have? That may be more of a hazard than anything - if there's too much suction you might need to rig up some type of guard or just change out the pump and filter as suggested by another person in the thread.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Oscillating water

    I can't believe a forum full of pool lovers keep suggesting to get a smaller pump....I say get a BIGGER pool if re-aiming doesn't work. :P
    6500 gal, Intex 18'x48" above ground, 1hp Pro Sand Filter, TF100 Test Kit

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    UnderWaterVanya's Avatar
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    Re: Oscillating water

    What's the plumbing hookup like - can you post pics? I wonder if you could put a T in and rig an extra return using PVC pipe or Intex hoses. You could do likewise on the suction side and add a skimmer if you don't have one now.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    asxetos's Avatar
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    Re: Oscillating water

    This thing is like standing (or stationary) waves, only they increase in height because they resonate with the flow waves created by the pump and gain energy until the water overflows, energy is then lost, and the phenomenon starts over again.

    If the pool had a different shape or different dimensions this would not occur, as the water surface would have a different natural frequency.

    In order to stop the phenomenon, you need to modify either the natural frequency of the water surface (by changing pool shape or dimensions) or the frequency of the flow waves created by the pump (by modifying the way water enters the pool).

    Returning water to the pool in a different way should do the job easily, maybe even try to return water from above if you like the sound of running water, it is a trial and error thing though.

    I would definitely like to see some pics of this thing before it goes away!
    Donīt be fooled by the sheep on my bike, I swim with fish in my sound equipped pool.

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    Mod Squad jblizzle's Avatar
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    Re: Oscillating water

    A video would be pretty interesting ... you are sure it is not a neighbor kid with a bunch of 20" subwoofers in their car or a herd of Brontosaurus' nearby right?
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    linen's Avatar
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    Re: Oscillating water

    Could post the model numbers/details for the pump(not just motor) and filter? You can have to much flow for a filter.

    I would love to see video of the oscillation
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  15. Back To Top    #15

    Re: Oscillating water

    Thanks for all these great replies--for now, I seem to have a temporary fix just by overfilling. This puts the return far enough below the surface of the water that it apparently doesn't get a chance to begin that back and forth motion that starts the oscillation.

    I think I will try the plumbing fix, adding an elbow to redirect the flow, and point along the wall, rather than out into the middle of the pool--certainly the round shape seems to have facilitated this, as someone mentioned--doubt it would happen with other than round shapes.

    I'll post the outcome, and if it happens again, will try to capture a video/pics.

    Thanks again

  16. Back To Top    #16
    linen's Avatar
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    Re: Oscillating water

    Oops, I forgot...

    Welcome to tfp, jnealhicks

    I would still be interested in your pump and filter models.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Oscillating water

    Quote Originally Posted by linen
    Oops, I forgot...

    Welcome to tfp, jnealhicks

    I would still be interested in your pump and filter models.
    Thanks for the welcome. Here's pump and filter model numbers--and it's 1.0 not 1.5HP as I stated earlier.

    Manufacturer: Ningbo Tuozhan
    Pump model: RS4G24213 (1HP 8.8 amps, 3450RPM, 75GPM)
    Filter Model: 73113 (70GPM design flow rate, 70 sq feet)
    Paid $399 for the pump & filter * cartridge, pre-assembled, and mounted on a platform.

    Also posted photos here: https://picasaweb.google.com/1112839772 ... directlink

    First photo shows how the return is submerged now--enough to stop surges
    Second photo is the motor specs (see above)
    Third photo filter specs (see above)
    Fourth photo shows how pump still shoots water 10+ feet, even though the return is submerged

  18. Back To Top    #18
    Mod Squad jblizzle's Avatar
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    Re: Oscillating water

    That picture sure looks like it is pointed up ... Can that blue piece just rotate to aim the water more circular or down?
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  19. Back To Top    #19

    Re: Oscillating water

    You're right, it points up. Unfortunately, the blue piece goes through the liner, and connects to the return hose on the outside of the pool. The weight of the hose pulling down on the outside of the pool, keeps the blue part pointing up on the inside of the pool. Off now to find some pvc parts for an attempted fix...

    Thanks

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    UnderWaterVanya's Avatar
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    Re: Oscillating water

    I'd guess there's a lot of MA in your future unless you get that pointed down. Aeration increases pH...
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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