Calculating flow through 2" overflow

frankr409

Feeder Fish
MFK Member
Dec 4, 2010
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Indiana
I wanted to wait until I actually started working with my contractor on the plumbing before I committed to a bulkhead size on the new 280 that I am putting in to service.

Essentially I am trying to figure out how much water flow I could REASONABLY expect through two 2" bulkheads that will be plumbed into one PVC pipe leading to my sump. I am aware of Hazen-Williams equations and so on, but do not wish to go that far with the calculations, I just want a reasonable guess if anyone has one. To clear up any confusion, the hole that the water goes through will be 2 inches.

Is anyone out there using a bulkhead that size for an overflow, and if so what would you approximate your flow rate to be. I saw a separate website http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml that suggests flow rates of an unimpeded pipe that size to be about 3300 gallons per hour for one hole.

If you want to do more than guess I will have several variables which I am certain would reduce that rate, although I'm not sure if it is substantial:

- At least 5 elbows I would think to snake into the sump behind the wall.
- Two 2" inch strainers.
- A gate valve to fine tune the exhaust flow somewhat, but assume it is wide open
- At least 15 feet of 2" Schedule 80 pvc.

Any thoughts will be appreciated, it will help me better plan the return side of the sump and I can at least get a pump that would perhaps give me more flow than I thought I might originally get when the plan was to do commercial overflow boxes.

Thanks!
 

frankr409

Feeder Fish
MFK Member
Dec 4, 2010
21
0
1
Indiana
Thank you, both of you. At last a believable number. I asked the same question at Simplydiscus, and the only thing you get there are arguments why you shouldn't do this or that. I believe I will match this with the Water Blaster HY-12500 as the head height should leave that pump just slightly below the exhaust rate of the two overflows.
 

frankr409

Feeder Fish
MFK Member
Dec 4, 2010
21
0
1
Indiana
Would you recommend trying to slow the pump with an in line gate or would you step down one model of that pump?
 

strollo22

Siamese Tiger
MFK Member
May 21, 2012
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Datnoid Island
I would personally rather have a pump that's rated a little higher than have one that may he rated lower after head loss. The next model down is 2600 gph so you figure with head loss about 2400-2500 gph. It's easier to throttle it back then it is to control how much water is flowing through the overflows


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