Water Flow Rate Calculation

[JJ]

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

[berkshire bill]

Don't know the specific for your situation, but the average would be 4.8 gpm.

Bill

[Craven Morehead]

Here's a worthless post for ya. The OP is asking for a SPECIFIC answer! Duh!

[Dennis J Sunday]

GPM=0.0408 x pipe diameter inches (sq) x feet/minute water velocity. Good Luck!

-- Best Regards, Dennis J Sunday Home Inspection Systems

[Bob]

SPECIFIC answer!

Followed by another worthless post. A specific answer would be meaningless due to insufficient information.

Bob

[Goedjn]

[Martik]

Is it operational? Get a 5gal container and time it with a stop watch.

[Rod]

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..

[Gary Slusser]

"JJ" wrote

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.

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

Gary Slusser's Help Forum www.qualitywaterassociates/phpBB2/

[Kevin]

[David Efflandt]

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.

[RB]

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:

[JJ]

Thanks to all for answering.

JJ

[Rod]

I think spouting off Reynolds numbers really helped... thanks for those...

[Bob]

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.

head loss of

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