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  • Results 1 to 7 of 7

    Thread: How much drawdown in a 4 foot long 4" pipe w/ two 90's at 8,629 GPH???

    1. #1
      Zac Penn is offline Supporting Member
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      How much drawdown in a 4 foot long 4" pipe w/ two 90's at 8,629 GPH???

      Just for fun, I disconnected the float on my ZacoDraco and cranked the FlowFriend up to 2600 RPM and the ultrasonic flow meter read 17,258 GPH. The ZacoDraco and Testing Tank are connected with two 4" pipes roughly 4' long, and a hard 90 at each end. The drawdown between the tanks was 7" under gravity flow conditions. So at 8,629 GPH each of those pipes had a 7" drawdown in order to flow that much water.

      Normally this kind of plumbing configuration would be able to achieve around 4,000 GPH with only a 1.75" drawdown between the tanks, so it really goes to show you that doubling the flow rate does not mean simply doubling the drawdown. I already knew this, but I figured it would be a fun learning experience for others. I did not know what the actual drawdown would be on that setup at max flow for the pump so I gave it shot.

      The pump was connected with a single 4" suction pipe about 5' long, with one hard 90 and a 4" swing check valve. The outlet was roughly 9' long with a Fernco 90, a hard 90 and a 4" ball valve.
      Total head height was 2' and power consumed was 760 watts.
      Not bad for a water pump and 2' of head could yield you a nice low profile shower like what Kimini built.
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    2. #2
      DragonFireSG is offline Senior Member
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      Quote Originally Posted by Zac Penn View Post
      Just for fun, I disconnected the float on my ZacoDraco and cranked the FlowFriend up to 2600 RPM and the ultrasonic flow meter read 17,258 GPH. The ZacoDraco and Testing Tank are connected with two 4" pipes roughly 4' long, and a hard 90 at each end. The drawdown between the tanks was 7" under gravity flow conditions. So at 8,629 GPH each of those pipes had a 7" drawdown in order to flow that much water.

      Normally this kind of plumbing configuration would be able to achieve around 4,000 GPH with only a 1.75" drawdown between the tanks, so it really goes to show you that doubling the flow rate does not mean simply doubling the drawdown. I already knew this, but I figured it would be a fun learning experience for others. I did not know what the actual drawdown would be on that setup at max flow for the pump so I gave it shot.

      The pump was connected with a single 4" suction pipe about 5' long, with one hard 90 and a 4" swing check valve. The outlet was roughly 9' long with a Fernco 90, a hard 90 and a 4" ball valve.
      Total head height was 2' and power consumed was 760 watts.
      Not bad for a water pump and 2' of head could yield you a nice low profile shower like what Kimini built.

      Interesting math there. Is it ~4000 gph per pipe at 1.75" drawdown?

      The gravity flow calculators suggest that those hard bends are adding about 50ft of pipe run. With the run lengths being constant, the math seems to agree for 1.75" head and 7" head.

      It would be interesting to see how the use of sweep elbows alter the system dynamics.

      Edit with screenshots

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      Last edited by DragonFireSG; 11-15-2018 at 10:30 PM.

    3. #3
      Zac Penn is offline Supporting Member
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      Quote Originally Posted by DragonFireSG View Post
      Interesting math there. Is it ~4000 gph per pipe at 1.75" drawdown?

      The gravity flow calculators suggest that those hard bends are adding about 50ft of pipe run. With the run lengths being constant, the math seems to agree for 1.75" head and 7" head.

      It would be interesting to see how the use of sweep elbows alter the system dynamics.
      Yes that was 4000 gph per pipe at 1.75" drawdown.
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    4. #4
      BWG is offline Senior Member
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      Is this gravity flow through the drum filter?

    5. #5
      Zac Penn is offline Supporting Member
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      No I removed one of the drums so it was free flow
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    6. #6
      BWG is offline Senior Member
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      If I put an Origin 25 in a raceway filter and flowed max 6,600 gph what difference in levels in/out could I expect clean?

    7. #7
      Zac Penn is offline Supporting Member
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      Quote Originally Posted by BWG View Post
      If I put an Origin 25 in a raceway filter and flowed max 6,600 gph what difference in levels in/out could I expect clean?
      I don't have exact numbers on that but assuming the flow numbers are achieved the same way between the Origins 16 and 25, then you should expect to see a 3/8" difference in water level caused by the resistance through the 58 microns screen. That is assuming you install it in the raceway similar to how I have them mounted in my filters. I cutout the huge entrance hole and bolt the casing to my filter so there is no restriction from the 4" inlet pipe going into the drum. If you use the two 4" inlet holes then I would expect a 1/2" - 5/8" difference.
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