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  • Results 1 to 9 of 9

    Thread: is bigger better ?

    1. #1
      bobbd's Avatar
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      is bigger better ?

      Is there any advamtage in gravity flow if you have a skimmer with a 3 inch outlet and connect 4inch pvc to it ?

    2. #2
      hp is online now Supporting Member
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      I think depending on how long the pipe line is after that. If it is long then it is benefitcial. If it is short then not much.

      Hp.

    3. #3
      malatu is offline Supporting Member
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      My thought is: No. It's my understanding is thatt a 4" pipe moving the same amount of water as a 3" pipe will flow with less velocity. As a result, solids could settle inside the pipe. Others will chime in if i'm giving you misinformation.

    4. #4
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      I think that pipe's flow rate is limited to the flow that is feeding it. If the 3 inch pipe is limited to a gravity flow of 8400gph you will never reach the full potential of 14,400gph on the 4 inch pipe. The three inch inlet acts as a choke point. Some gravity pressure may push you a bit beyond the 8400gph, but never to the full 14,400. I believe you can find a pool skimmer or similar on this site that can be purchased at 4 inches or modified for 4 inches to obtain max flow rate.



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    5. #5
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      Gravity flow requires some head loss to create flow. The amount of head loss is determined by the type of pipe, the length of pipe, the diameter of the pipe as diameter determines both velocity and surface area for friction. If the draw from the pump at the other end of the gravity flow is not drawing more than the pipe can furnish within the head losses needed, then the system will work. If the head losses exceed the permitted head losses at the flow required, the system fails.

      Going from 3" pipe from the skimmer to the 4 inch should have very little effect, unless the flow is great, at which point there will be turbulence created at the transition, which will cause flow reduction.

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    6. #6
      hp is online now Supporting Member
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      Ideally, you want 4" skimmer. But if you have to stuck with 3", by connecting it to the 4", the fiction loss will be less and it will help the flow if the pipeline is long.

      Another thing for gravity flow is that you want to keep the outlet submerge in the water, especially if you connect it to the 4" pipe. It keeps the air out and maximize the pulling force.

      hp.

    7. #7
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      What is the targeted flow rate via gravity? What is the distance to the filter pit mechanical stage?

    8. #8
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      Quote Originally Posted by bobbd View Post
      Is there any advamtage in gravity flow if you have a skimmer with a 3 inch outlet and connect 4inch pvc to it ?
      Yes, 100%, it is no problem. If you are connecting 4" pipe right at the skimmer with a bushing then you have the advantage of 4" pipe which allows for a higher flow rate. Even if you went 3" in the whole way it would also be fine as you are probably not going to exceed 2 or 3 thousand gallons per hour. Doesn't matter if it is short or long.
      people like to vehemently defend their purchases and find it incredulous that anything could be better

    9. #9
      coolwon is offline Senior Member
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      Quote Originally Posted by bobbd View Post
      Is there any advamtage in gravity flow if you have a skimmer with a 3 inch outlet and connect 4inch pvc to it ?
      Less likely to block and easier to rod if it does.

      Garfield
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