# Manning's Equation Question



## civilrobot PE etc etc (Jan 3, 2020)

How do you know when to use Hazen - Williams vs the Darcy-Weisbach equation?


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## squaretaper LIT AF PE (Jan 3, 2020)

As far as the exam is concerned, I only ever used DW for closed pipe, and HW for open channel flow...might be oversimplifying it, but that's what comes to mind at the moment.

Edit: also mechanicals rarely use HW, at least in my experience. Also, DW is good for gases and other stuff besides water. HW is water only, I believe.


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## Will.I.Am PE (Jan 3, 2020)

For pipe flow, you can use either. It would just be about what you're given in a problem. 

For example:

f = 0.015 - definitely Darcy-Weisbach

C = 120 - definitely Hazen-Williams


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## civilrobot PE etc etc (Jan 3, 2020)

thanks @squaretaper LIT AF PE

@Will.I.Am PE thanks!


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## squaretaper LIT AF PE (Jan 3, 2020)

Will.I.Am PE said:


> For pipe flow, you can use either. It would just be about what you're given in a problem.
> 
> For example:
> 
> ...


Neat! Elegant way of putting this. You're the hero EB needs, not the one it deserves. :rotflmao:


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## squaretaper LIT AF PE (Jan 3, 2020)

civilrobot said:


> How do you know when to use Hazen - Williams vs the Darcy-Weisbach equation?


Also, another "trick" I learned was that even if not given, you can kinda-sorta-maybe get away with just assuming f=0.02 if it's water problem and proceed with solving DW. Be super careful about using this assumption, but if you're lucky, it might save you a few steps and a nice trick to keep in your back pocket. I used it once or twice, caveat emptor.


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## civilrobot PE etc etc (Jan 3, 2020)

squaretaper LIT AF PE said:


> Also, another "trick" I learned was that even if not given, you can kinda-sorta-maybe get away with just assuming f=0.02 if it's water problem and proceed with solving DW. Be super careful about using this assumption, but if you're lucky, it might save you a few steps and a nice trick to keep in your back pocket. I used it once or twice, caveat emptor.


yeah I have this written into my notes. 

if i'm given both f and C, I will use both to solve for the answer and review the options to select the available answer. that's the conclusion I needed to get to. I thought I was missing some other small elemental detail but @Will.I.Am PE confirmed that it's an either/or scenario.


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## squaretaper LIT AF PE (Jan 3, 2020)

Might be good to edit your quotation. I changed my original post to the correct "0.02", but you beat me to it! I'd hate for someone to use bad information... Apologies for fat fingers.


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## civilrobot PE etc etc (Jan 3, 2020)

squaretaper LIT AF PE said:


> Might be good to edit your quotation. I changed my original post to the correct "0.02", but you beat me to it! I'd hate for someone to use bad information... Apologies for fat fingers.


done!


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## squaretaper LIT AF PE (Jan 3, 2020)

Ughh...thanks to you I'm inspired to work on my study schedule. Boo...


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## civilrobot PE etc etc (Jan 3, 2020)

squaretaper LIT AF PE said:


> Ughh...thanks to you I'm inspired to work on my study schedule. Boo...


another PE?


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## squaretaper LIT AF PE (Jan 3, 2020)

civilrobot said:


> another PE?


Electrical - Power. I explained it in the Power thread (no expectation for you to read all that), but basically I R super, super bad at strategy and I don't qualify for the license at this time. Buuuuut, I *DO* qualify for the electrical if I pass the stupid exam so...I'm still going to be around (and I'm basically doing it to make more money, stupid CA real estate pricing cleaned me out). Aaaanyway, you have another study buddy. You can do it! Go! Go! @civilrobot


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## civilrobot PE etc etc (Jan 3, 2020)

squaretaper LIT AF PE said:


> Electrical - Power. I explained it in the Power thread (no expectation for you to read all that), but basically I R super, super bad at strategy and I don't qualify for the license at this time. Buuuuut, I *DO* qualify for the electrical if I pass the stupid exam so...I'm still going to be around (and I'm basically doing it to make more money, stupid CA real estate pricing cleaned me out). Aaaanyway, you have another study buddy. You can do it! Go! Go! @civilrobot


this is amazing!! i'll head over to power to read about it.


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## squaretaper LIT AF PE (Jan 3, 2020)

civilrobot said:


> this is amazing!! i'll head over to power to read about it.


Ehh, don't waste your time doing that. Go study!


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## civilrobot PE etc etc (Jan 8, 2020)

squaretaper LIT AF PE said:


> Ehh, don't waste your time doing that. Go study!


lol I started back on Monday.


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