Carrier Water Pipe Sizing

[boatnerd]

I am using an existing 3" plant water line that runs under 40 psig as a source of carrier water to convey a treatment chemical to a water channel approximately 500 feet away. I need to determine if I have enough pressure to get the water and chemical through a new 2" pipeline to the channel. I want to compute the friction losses due to fittings and valves but need a fluid velocity in the 2" line. How do I determine the flow rate in the new pipeline and subsequently the fluid velocity so I can compute these friction losses in terms of velocity heads? Is this an iteritive process?

 

[bimr]

Chemicals are typically diluted to 5% strength for day tanks, etc. Without know more, assume a chemical strength of 5%.

Use a fluid velocity of 3-6 ft/sec.

 

[Artisi]

If you need 40PSI to get X quantity of water thru 500ft of 3" pipe and as friction increases to the 5th power for pipe dia. change then it follows you will need 2/3^5 *40 which equals 300 PSI to achieve the same flow rate.

Alternately if you have 40PSI available you will get something less than 100 GPM thru your 2"line.

 

[cvg]

I am getting conservatively) 30 gpm through the 2" pipe at a velocity of about 3 fps using Hazen Williams chart. If you have any elevation differences, fittings, valves or other restrictions or need for residual pressure, this number may be less. If you use very smooth pipe such as pvc, you could get closer to 40 gpm.

 

[bimr]

For a velocity of 3 ft/sec (68 gpm) in a 3" dia pipe, that would be a headloss of around 2.2 feet per 100 feet of pipe. For 500 feet of pipe, assuming a few elbows, that would be a headloss of 13.2 feet or approximately 6 psi.

For a velocity of 6 ft/sec (137 gpm) in a 3" dia pipe, that would be a headloss of around 8 feet per 100 feet of pipe. For 500 feet of pipe, assuming a few elbows, that would be a headloss of 40 feet or approximately 17 psi.

For a velocity of 3 ft/sec (30 gpm) in a 2" dia pipe, that would be a headloss of around 3.5 feet per 100 feet of pipe. For 500 feet of pipe, assuming a few elbows, that would be a headloss of 21 feet or approximately 9 psi.

For a velocity of 6 ft/sec (62 gpm) in a 2" dia pipe, that would be a headloss of around 12.2 feet per 100 feet of pipe. For 500 feet of pipe, assuming a few elbows, that would be a headloss of 40 feet or approximately 32 psi.

It looks like if you used the 2" diameter pipeline, it would have 1-1/2 to 2 times the headloss of the 3" diameter pipeline.