# Water Flow Rate Calculation

• posted on January 6, 2004, 10:09 am
Hi,
I looked arounf the Internet for this, but I could not find a good source. I am trying to calculate the following:
3/4" copper pipe 100 psi 40F water
What is the flow in gal/min?
Thanks,
John
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• posted on January 6, 2004, 11:58 am

I
Don't know the specific for your situation, but the average would be 4.8 gpm.
Bill
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• posted on January 6, 2004, 2:26 pm
Here's a worthless post for ya. The OP is asking for a SPECIFIC answer! Duh!
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• posted on January 6, 2004, 4:55 pm

Followed by another worthless post. A specific answer would be meaningless due to insufficient information.
Bob
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• posted on January 6, 2004, 4:25 pm
GPM=0.0408 x pipe diameter inches (sq) x feet/minute water velocity. Good Luck! -- Best Regards, Dennis J Sunday Home Inspection Systems Www.homeinspectionsystems.com

I
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• posted on January 6, 2004, 6:52 pm
http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm has an online calculator, but it requires you to guess the friction losses, and also wants metric units. Remember to subtract the 15PSI atmospheric from your 100PSI supply to get an effective 85 PSI pressure drop.
JJ wrote:

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• posted on January 7, 2004, 7:49 am

Huh? If you have 100 psig (gauge pressure) in and 0 psig out, that is 100 psi differential, but only under static (no flow) conditions. Under flowing conditions supply pressure will drop based on head loss of undisclosed piping to that point and undisclosed equivalent length of piping after that point. Basically insufficient data to even take a wild guess.

--
David Efflandt - All spam ignored http://www.de-srv.com /
http://www.autox.chicago.il.us/ http://www.berniesfloral.net /
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• posted on January 9, 2004, 12:32 am
wrote:

friction
that is 100

Which could never occur. If there is no flow, there is no pressure drop in a horizontal pipe. There will be no differential. If there is differential, there is flow.

Which can be assumed in most residential applications to be negligible.

None was mentioned. If the pressure is 0 psi out, one could safely assume that there is no pipe beyond, or it has no effect.

If you know the input pressure and output pressure and the pipe length and diameter you should be able to make a reasonable calculation. Without the pipe length, as origionally stated, you cannot.
Bob
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• posted on January 6, 2004, 10:17 pm
On Tue, 06 Jan 2004 03:09:35 -0700, JJ wrote:

Is it operational? Get a 5gal container and time it with a stop watch.
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• posted on January 6, 2004, 11:08 pm
If you have 100 psig right at the opening of the 3/4" pipe you will get about 168 gpm. I'm curious what u are up to with this...
I have a chart... if u want it... ask me for it..

I
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• posted on January 7, 2004, 2:21 am

I
I don't know about the temp but at 80 psi in 3/4" L copper you'll have 30 gpm out of a 100' of it. http://www.tpub.com/utilities/19.htm
I used to have a better chart but the page doesn't work now. You have too much pressure for water line, the velocity will be way too high. Max velocity should be about 5-6 ft/s.
Gary Quality Water Associates www.qualitywaterassociates.com Gary Slusser's Help Forum www.qualitywaterassociates/phpBB2/
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• posted on January 7, 2004, 3:50 am
http://www.bellgossett.com/software.stm System Syzer should help.
wrote

source.
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• posted on January 7, 2004, 7:54 am
What length is the pipe? What pressure drop are you willing to encounter?
Assuming a 100 ft length of smooth (similar to electropolished) 3/4" L copper tubing which will have an ID of 0.668 inches the flows look like this:
Flow Pressure Reynolds rate Drop Number 19 gpm     95.38 psi 56,240 15 gpm     59.49 psi 44,400 10 gpm 26.48 psi 29,600 5 gpm 6.65 psi     14,800 0.75 gpm 0.15 psi 2,220
The last flow of 0.75 gpm is just about at the transition between laminar and turbulent flow. (I like to use a Reynolds number of 2,300 as the transition.) For the higher flow rates, as turbulence increases so will the noise from flowing water.
You can see that at 19 gpm water will emerge from the pipe but with virtually no pressure at the outlet.
Interestingly your temperature is near the point where water's density drops markedly and where it's viscosity starts to increase quickly. These pressure drops will change (improve) as the temperature is increased.
I believe these numbers to be correct but since I didn't have a calculator handy when I did the you'll have to accept slide rule calculations.
RB
JJ wrote:

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• posted on January 7, 2004, 10:14 am
JJ

increased.
source. I

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• posted on January 7, 2004, 12:40 pm
I think spouting off Reynolds numbers really helped... thanks for those...

increased.
source. I