Equivalent Diameter
Equivalent Diameter
(OP)
I am looking for a table or chart that shows equivalent diameter between 2 or 3 smaller diameter pipes and one larger diameter (for water main). For example, a 12" diameter main has the same capacity as two 8" mains.
I remember seeing some tables on the internet some time ago, but just can't find it now.
I remember seeing some tables on the internet some time ago, but just can't find it now.





RE: Equivalent Diameter
See the parallel pipes calculator in the attached link.
http://kirkmansoftware.com/
RE: Equivalent Diameter
BUT caution. It is almost never economical to replace a single larger pipe with two or more smaller pipes. For example:
Flow = 1000 gpm
Length = 1000 ft
Capacity of 12" pipe @ 5 ft/sec = 1762 gpm
Capacity of (2) 8" pipes @ 5 ft/sec = 1567 gpm
Velocity of 12" pipe @ 1000 gpm = 2.84 ft/sec
Velocity of each 8" pipe @ 1000 gpm = 3.19 ft/sec
Head Loss of 12" pipe @ 1000 gpm = 14.04 ft per 1000 ft
Head Loss of (2) 8" pipes @ 1000 gpm = 38.48 ft per 1000 ft
Add to this the cost difference in installed cost and energy costs over the life of the pipeline and you'll find a huge advantage for the single larger pipe.
good luck
RE: Equivalent Diameter
Thanks again
RE: Equivalent Diameter
RE: Equivalent Diameter
Decide on the flow you want to transmit; say 1000 gpm
Guess at a nominal pipe size in inches: say 8-inch
Square the pipe size in inches: 8x8 = 64
Multiply this number by 10; 10x64 = 640
This is the approximate capacity, in gpm of an 8-inch pipe flowing at about 3 to 6 feet per second.
That is: an 8-inch pipe can carry about 640 gpm.
Two 8-inch pipes can carry about 2x640 = 1280 gpm.
From this you can conclude that an 8-inch pipe is about the right size. This will get you within a pipe size of the "correct" answer.
You can easily use this kind of logic to arrive at any number of equivalent pipes without creating a table or doing a lot of complicated math.
good luck