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 This topic has 4 replies, 4 voices, and was last updated 17 years, 7 months ago by PLUMBILL.

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13 Sep 2006 at 2:34 pm #277906MasterPlumbersKeymaster
I am an inspector for a local jurisdiction. My coworker, the plumbing inspector, is taking a course and we are trying to find the answer to a mathematical question. We think the formula offered by the instructor may be missing something. Can anyone offer the formula for the following problem.
A six in pipe is 64 feet 2 inches long. How long would a 3/8 in pipe need to be to carry the same amount of galllons of water.
Thank you for your help.

14 Sep 2006 at 1:13 am #297351Bill KParticipant
J,
I come up with 16,384 ft long. This is “assuming” that the 6″ pipe is 6″ id and the 3/8″ pipe is 3/8″ id.What does your instructor say ?
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Â» This message has been edited by Bill K on 14 September 2006
» This message has been edited by Bill K on 14 September 2006

14 Sep 2006 at 1:31 am #297352Bill KParticipant
J,
The way I came up with this answer was as follows.The volume of a tube is: pi (3.1416) 1/2 the diameter 1/2 the diameter the length
So for your 6″ pipe the volume is 3.1416 3″ 3″ 768″ = 21,714.739 cubic inches.
Then you use the same formula but you have to figure out the volume of the 3/8″ pipe only 1 inch long which would be: 3.1416 .1875″ .1875″ 1 = .1104468 cubic inches.
Then you have to take the volume of the large pipe and divide it by the volume of a one inch long piece of the small pipe and you get 21,714.739 divided by .1104468 = 196608 inches which is 16,384 ft.
You could convert the cubic inches to gallons, but to solve this problem it is not needed.
I have sort of simplified this not knowing your math background.
The formula for volume is actually Pi R R length.
Where Pi is 3.1416, R is the Radius ( 1/2 diameter)
Bill Koustenis
Advanced Automotive Machine
Waldorf Md 
14 Sep 2006 at 10:49 am #297353Retired plbg1Participant
From my old Plbg book
The sq. of the Dia. of the pipex0.7854 will give the area of the openning of the pipe.
Dia. of pipe in ins. sq. .0408 will give thenumber of Gal. in a foot of pipe. Thats the best I can do let me know, retired plbr at trade 55 Yrs.
Art retired plbg 
15 Sep 2006 at 9:58 pm #297354PLUMBILLParticipant
A 6″ pipe holds 1.47 gallons per foot.
A 3/8″ pipe holds 0.005 gallons per foot.
You should be able to take it the rest of the way, good luck.


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