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  • Results 1 to 11 of 11

    Thread: Consistency of Pump Flow

    1. #1
      Diegar's Avatar
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      Lightbulb Consistency of Pump Flow

      Good morning. Working out some of the final details of my pond and have an anomaly i need sorted before i start trying to take action. I'm hoping that the wealth of experience here will know exactly why this is happening, and save me from many wrong guesses, if possible.

      I have water from a bottom drain and skimmer feeding into my sieve via gravity. The pump, an Evolution Series ES2500, is pulling from the bottom chamber of the sieve through 2" PVC. The pump is one of two, but only showing one for this issue. The pump then pushes the water through 2" PVC up 44" before it turns 90 degrees and falls into the bottom of the barrel filter. At the bottom of the barrel, the water is divided into two streams shooting opposite each other, and creating a vortex which rises upward to fill the barrel. There is media in the barrel, but this seems to happen with or without it, so ignoring it for now. The two small floating circles represent pond returns. The smaller is 1" PVC and drops water through a UV before sending it into the pond. The larger is 2" pvc and has a ball valve on it, but drops water into the pond. With the ball valve all the way open, the water level in the barrel stays near the top of the 2" return, but also fluctuates, but not as much.

      With the ball valve partially closed, the water level rises and will eventually fall out of the upper 2" opening, which becomes a waterfall. My issue is the water level will not stay in one place. The pump pushes water up and then almost as if the pump gives up, the water level will fall. When i look in the sieve, i can see the lowering water backing up into it, which the other pump helps to compensate for. I'm trying to understand why it might be doing this

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      Some points:

      1. The pump is rated for 2500 gallons at 5'. It's a continuously spinning DC motor connected to an impeller. No piston

      2. With the ball valve open, the fluctuation is several inches. With it partially to full closed, the fluctuation in water level is closer to a foot

      3. If i turn off the other pump, it stops doing this, and the water level in the barrel stays pretty constant. The weir in the sieve is also considerably higher, and have to reduce BD flow to get anything coming in through the skimmer.

      4. With both pumps on, the water level in the sieve's lower chamber remains above the outlets that feed the pump

      I'm thinking it's less an issue of available water, and more toward it being turbulent water. With the weir more open, the water rushes in faster, and wondering if bubbles could be getting into the pumps impeller. Has anyone run into issues with their pump's impeller giving out over and over? Wondering if some kind of divider in the sieve's lower chamber might help calm the water down before it gets to the outlets. Thinking out loud, and if i can modify the sieve, i will. If i have to rebuild it, i can do that too, but would rather not.

      Here is a rough idea of the sieve's body:

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      Sieve is 18" from front to back and 12" wide. Water flows in on the left side and over the weir, down through a screen which sits on the lip of that smaller chamber on the right. With both pumps going, i keep the water level along the wall of that right chamber, and under it, there's about 5" of clearance, with the outlets to the pumps being at the bottom.

      Any thoughts?
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

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    2. #2
      Diegar's Avatar
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      So i turned off the other pump and pulled the screen from the sieve. The water level in the bottom of the sieve stayed constant and everything was fine.

      Then i turned the other pump back on, and I hold the weir down all the way. This causes the water in the sieve to rise way up above where it should be, but it's still happening. Either the water is much rougher at high volume and needs to be controlled somehow, or i dunno, maybe it's a power issue? I find power to be a difficult idea to grasp, because they are low power high efficiency pumps, on a 12 gauge line, connected directly to the outside breaker box.. I would think my A/C unit would suffer before these pumps.. Still thinking...
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

    3. #3
      danbo is offline Senior Member
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      Not 100% sure on this, but some thoughts. "The two small floating circles represent pond returns" might be the key as they represent connections (head connections) to your pond. As your pond probably has a large surface area the level there may be fairly stable for the most part. But for sure, any change in the pond level (head) will reflect back on your system as shown and affect flows. Check https://www.engineeringtoolbox.com/p...ial-d_636.html re pumps in parallel. You are operating at point three in the graph. Any change in the pond level will reflect back on the pump head, affecting flows. The issue is time. Flows in m3/hr (or whatever units) translate to pond level rise or fall in a complex time based formula. Steady state, after time has passed things should stabilize you would think. But not always, often because we are too impatient. I have a complex pond arrangement. When there is heavy rain, level goes up. I dump water to a storage tank. If the quantity of water dumped = quantity of water caught by my pond/river system, then perfection: All levels should equalize. But I seldom get it right and paradoxically when there is heavy rain, my RDF 'fails' and I pump out water leaving my system at low levels.

      It's late here, it's Friday night. I've had a few beers, a couple of glasses of wine and a Black Label thinking about this. My feeling is that you have a complex arrangement (like many of us I guess) and the phenomena you see is a complex flow/level/TIME related issue. We all understand flow and levels, and that levels can affect flows. But we never take into account the TIME it takes for flows to affect levels. Not sure if this helps.....

      Meanwhile, I have a tropical storm outside. Off to dump some (but not too much) water to storage.

      Dan

    4. #4
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      Quote Originally Posted by danbo View Post
      Not 100% sure on this, but some thoughts. "The two small floating circles represent pond returns" might be the key as they represent connections (head connections) to your pond. As your pond probably has a large surface area the level there may be fairly stable for the most part. But for sure, any change in the pond level (head) will reflect back on your system as shown and affect flows. Check https://www.engineeringtoolbox.com/p...ial-d_636.html re pumps in parallel. You are operating at point three in the graph. Any change in the pond level will reflect back on the pump head, affecting flows. The issue is time. Flows in m3/hr (or whatever units) translate to pond level rise or fall in a complex time based formula. Steady state, after time has passed things should stabilize you would think. But not always, often because we are too impatient. I have a complex pond arrangement. When there is heavy rain, level goes up. I dump water to a storage tank. If the quantity of water dumped = quantity of water caught by my pond/river system, then perfection: All levels should equalize. But I seldom get it right and paradoxically when there is heavy rain, my RDF 'fails' and I pump out water leaving my system at low levels.

      It's late here, it's Friday night. I've had a few beers, a couple of glasses of wine and a Black Label thinking about this. My feeling is that you have a complex arrangement (like many of us I guess) and the phenomena you see is a complex flow/level/TIME related issue. We all understand flow and levels, and that levels can affect flows. But we never take into account the TIME it takes for flows to affect levels. Not sure if this helps.....

      Meanwhile, I have a tropical storm outside. Off to dump some (but not too much) water to storage.

      Dan
      I should have explained myself better with regards to the second pump, so my apologies. The second pump also pulls from the bottom of the sieve, but then returns water directly to the pond. Also, the whole barrel filter is sitting above the pond level, and I know my diagram didn't show that very well. The two returns on the side of the barrel are dropping water down below the barrel and into the water.

      Additionally, i wanted to rule out power as a cause.. The line is rated for 2400 watts and with a watt meter, i tested both pumps and the U/V clarifier and didn't come close

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      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

    5. #5
      hp is offline Senior Member
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      The first pump return is directly to the pond, which mean less head and will pull more water. How close are the two inputs to the pump? Can you extend the input of the "problem pump' further apart from the first one and test again with the weir down and see what happen? With this, I would think less turbulent at each input.

      fyi.. Been following your build and your skills are amazing..

      hp.

    6. #6
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      Quote Originally Posted by hp View Post
      The first pump return is directly to the pond, which mean less head and will pull more water. How close are the two inputs to the pump? Can you extend the input of the "problem pump' further apart from the first one and test again with the weir down and see what happen? With this, I would think less turbulent at each input.

      fyi.. Been following your build and your skills are amazing..

      hp.
      That makes sense, and wondering if there's cavitation happening right before the water leaves the sieve.

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      The outlets on the sieve are static, and the pump inlet lines are glued into place. Trying to find a solution that doesn't include taking everything apart. Can flow be reduced on a pump? Can i safely cause the 2nd pump to take in less water? First thing that comes to mind is to choke the pump inlet, or outlet with a small diameter pipe, but would that cause issues down the road, like a burnt out pump motor?
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

    7. #7
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      Quote Originally Posted by hp View Post
      The first pump return is directly to the pond, which mean less head and will pull more water.
      Specifically this.. I had thought about the capabilities of each pump by themselves, but didn't consider this aspect. If i can't safely reduce the intake of the 2nd pump, i will have to redesign the sieve body
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

    8. #8
      hp is offline Senior Member
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      The symptom is like cavitation. If you want to reduce the flow then put in a ball valve at the output of the pump, not in front. This should not hurt the pump, you mainly increase the dynamic head when you reduce the flow. It may hurt the pump if you reduce the inlet. You don't want to reduce the pipe size because it will limit your options. The ball valve give you options to adjust the output as needed.

      hp.

    9. #9
      Diegar's Avatar
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      Quote Originally Posted by hp View Post
      The symptom is like cavitation. If you want to reduce the flow then put in a ball valve at the output of the pump, not in front. This should not hurt the pump, you mainly increase the dynamic head when you reduce the flow. It may hurt the pump if you reduce the inlet. You don't want to reduce the pipe size because it will limit your options. The ball valve give you options to adjust the output as needed.

      hp.
      This sounds like my next step. Thank you everyone!!
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

    10. #10
      hp is offline Senior Member
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      For testing, I think you could probably hold a 3" pipe at the 2nd pump input to extend it out and see if it solves the problem. If it does, I think you could find a way to make it permanent or install a wall/divider at the lower chamber to make it 2 separate section? Just thinking it out loud .

      The last option is to reduce the output (if it solves the problem) without rebuilding the whole thing. You want to maximize your pump capability.

      hp.

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    11. #11
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      Installed the ball valve on the output of pump #2, and that worked, but i had to turn it too much for it to stop hogging the water, so next I'm going to try adding a vertical divider in the bottom of the sieve between the right and left outlets, and see how that works out
      "If you want good clean high quality oats you must pay a fair price for them. If however you chose to purchase oats that have already gone thru the horse, they come a little cheaper." - Dick Benbow

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