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Old 03-08-2010, 10:31 AM   #1
mr_bones4
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Default Question for you... 3/4" line at 65 PSI how many GPM?

I haven't been able to figure this out so I'm going to iFish

I have a 40ft long 3/4" pipe flowing water at 65 psi. How many GPM is the line flowing?

Thanks.

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Old 03-08-2010, 10:39 AM   #2
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Time how long it takes to fill a barrel in seconds. Divide by 55 and multiply by 60. That's how many GPM. About 45
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Old 03-08-2010, 11:12 AM   #3
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

I have a well set at 40-60 for a 50 psi average. a 3/4" frostfree faucet flows approximately 15 gallon per minute. But it is probably restricted to about a 5/8" flow. There is a calculation you can find by google.
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Old 03-08-2010, 11:32 AM   #4
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Quote:
Originally Posted by Chrome Bumper View Post
Time how long it takes to fill a barrel in seconds. Divide by 55 and multiply by 60. That's how many GPM. About 45
It was a leak and is no longer flowing. Good idea though.
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Old 03-08-2010, 11:33 AM   #5
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Quote:
Originally Posted by baltz526 View Post
I have a well set at 40-60 for a 50 psi average. a 3/4" frostfree faucet flows approximately 15 gallon per minute. But it is probably restricted to about a 5/8" flow. There is a calculation you can find by google.
I have looked all over google but haven't found an equation that fits what I'm looking for. Thats why I turned to iFish.
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Old 03-08-2010, 12:54 PM   #6
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

What schedule of pipe is it? Sch. 40 and 80 have a different wall thickness, therefore for the gpm will be different.
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Old 03-08-2010, 01:16 PM   #7
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Where was the 65 psi measured at? Was it 40 feet from a clean broken 3/4" opening?
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Old 03-08-2010, 01:39 PM   #8
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

There is no way to tell exactly how many GPM knowing only pipe size and pressure. If you knew the velocity then you could figure out the GPM. You can flow 20 GPM through 3/4" pipe or 12 GPM at the same pressure through the same size pipe. The 20 GPM would have alot faster velocity than the 12 GPM but the pressure could be the same. As a guess I would put your flow between 12 and 15 GPM.
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Old 03-08-2010, 01:44 PM   #9
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?


Without velocity volume can not be determined.
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Old 03-08-2010, 04:25 PM   #10
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

gpm = 29.7 times the the diameter (inside) squared times the square root of the discharge pressure. so.

= 29.7 times (.75 x .75) x 8 = approx 133.64 gallons max can flow per minute

or something like that.......
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Old 03-08-2010, 06:35 PM   #11
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Google "Hazen Williams Equation", it's an older empirical method that lends itself well to this type of problem

Assuming it's PVC pipe and the "leak" is totally open (like Snapset asked), i.e the pressure at the leak = zero (atmospheric), I get about 35 gpm. If the "leak" is just a crack in the pipe and soil is exerting pressure on the leak it would be quite a bit less than this
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Old 03-08-2010, 06:45 PM   #12
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

3/4" ID or OD?
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Old 03-08-2010, 06:57 PM   #13
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Quote:
Originally Posted by Radioactive View Post
gpm = 29.7 times the the diameter (inside) squared times the square root of the discharge pressure. so.

= 29.7 times (.75 x .75) x 8 = approx 133.64 gallons max can flow per minute

or something like that.......
That's the formula!
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Old 03-08-2010, 08:18 PM   #14
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

You also need to know the friction loss which is mostly based on the length of the pipe and what it is made from (PVC, steel, Cu etc.)


Google Irrigation Tutorials.
You will most likely find an easy to use formula among the many given there.
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Old 03-08-2010, 09:28 PM   #15
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

I think .75x.75=0.5625x29.7=16.70625 gallons is correct. 1002.375 gallons per hour, 24,057 gallons per day, 168,399 GPW, 673,596 GPM. I have seen water bills like this on frozen houses, when lines burst. It is always bad news when a customer call and says: can you check my house? i got a $360 water bill last month.
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Old 03-08-2010, 09:41 PM   #16
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Default Re: Question for you... 3/4" line at 65 PSI how many GPM?

Based on an assumed flow velocity of 10 feet per second, it would be about 13 gallons per minute. But it's impossible to calculate without knowing the piping configuration. Every elbow, "T" and valve contributes to friction losses. You would have to add up the friction losses from the pipe itself, and all the fittings, to solve the problem.
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