Oscillating water

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jnealhicks

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Jul 23, 2012
7
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
 
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.
 
JohnT said:
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.
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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
 
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.
 
UnderWaterVanya said:
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.
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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.
 
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?
 
cramar said:
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?
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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.
 
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.
 
jnealhicks said:
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??
Click to expand...

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.
 

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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.
 
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!
 
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
 
linen said:
Oops, I forgot...

Welcome to tfp, jnealhicks :wave:

I would still be interested in your pump and filter models.
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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
 
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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