Size of Washout line

[sowhatso]

For the water main transmission pipelines , can you help me in getting the data for selecting the size of the washout line depending on the size of the main transmission line ??

If there is any table that provide this data this will be vey helpfull , thanks in advance ..

 

[rconner]

You might want to clarify exactly what you mean by “washout line” (and/or all functions you wish the “washout line” to accomplish in your specific applications?) to get responses maybe from folks more directly knowledgeable than I to your inquiry. If you are however talking about blow-off or system drains etc. (that I think are often located at low spots in the system, and/or where there can be suitable means of water disposition available etc.), I’m not sure I’ve seen much in standards or common literature/manuals specifically discussing all considerations that might be involved in such.
Nevertheless, I suspect that with a good web search engine and a few keywords you could probably find many practices/designs of different large utilities etc. to look at (e.g.

http://www.wsscwater.com/business/PDMANUAL/PipelineDesignManualPART_ONE/W-23-2008.pdf

etc.)
Now I guess once you know exactly what you want to/or what controls what you do, there may indeed very well be some tables available that might be helpful in determining some effects of sizing blow-off piping and other structures/matters etc. [e.g. per Table No. 17-1 pages 17-5 through 17-8 at

http://www.acipco.com/adip/products/Sect17.pdf

, and that per this table a flow rate of 1,400,000 MGD (or ~970 gpm) e.g. out from one 6” hydrant lead would result in ~2.54 fps flow velocity in a 12” mainline (if nothing else was also drawing from the main at that time), whereas the flow velocity in the hydrant lead would be ~10 fps during that amount of withdrawal.]

 

[coloeng]

As rconner indicates, you need at least 2.5 fps velocity in the main you want to flush out in order to scour any sediment out of lthe pipe. The size of blowout, or I assume what you are calling a "washout line" is the same thing, will depend on the pressure that you have. The lower the pressure the larger a blowoff you will need.