Twin Force Main

[redbridge]

I am working on a project that consist of twin force mains (6-inch and a 4-inch). I am planning on using an 18" casing pipe which will be shared by the twin force mains. I am wondering if anyone has a detail drawing or specification for this. This is a 280' highway crossing. I would appreciate any feed back.

 

[rconner]

I believe some casing spacer folks can furnish specially designed spacers for multiple carrier pipes up inside casings (e.g. see pg 7 at

http://www.apsonline.com/pdf/CASING/CasingSpacers.pdf).

While I don't have any experience with such to know if it is a practical problem, I think it may not be a bad idea to additionally put some sort of guides or tracks longitudinally in on the casing wall to defeat any tendency of the cluster to "rotate" out of the clock orientation you intend for the two carrier pipes, as the bundled inside lines are pushed or pulled etc. up inside same.

 

[CivEnvEng98]

Lburg 2 questions:

1) is this a j & b or a hdd?
2) why not combine the 2 force mains and go with 1 pipe?

 

[redbridge]

CivEnvEng98,

We are using 2 pipes because the initial flow is pretty low. The project is for a proposed industrial park. The 4-inch force main will be used mainly for a couple of small subdivisions. I guess to answer your question it is because of the velocity in the pipes. This will be a bore. I think that is what you are asking in your first question.

 

[CivEnvEng98]

Curious to see a utility approve a dual FM scenario for such small diameter lines.

Anyway, rconner has a good spacer manufacture listed.

Here are brochures to 2 more that I've used:

http://www.cascademfg.com/uploadedFiles/All Stainless Steel Casing Spacer Brochure.pdf

http://www.pipelineseal.com/pdf/h2o_12-3-03.pdf

 

[redbridge]

CivEng98

The utility requested dual force mains. I recommended one 8" but they are worried about sewage staying in the lines too long. The force main is about 22,000 feet long and they don't expect the industrial park to develop for several years. The 6" line may never get used. They build all kinds of industrial parks around here that sit empty. What is your opinion on using an 8" force main that will only see about 10,000 gallons per day initially. Thanks for you input.

 

[cvg]

why not put just the 8 inch line through the casing and go back to the double pipe on either end? This will be easier than trying to thread two pipes through one casing.

 

[CivEnvEng98]

Lburg I hear what the utility is wanting, but it seems to me that a single 6" would be the compromise between sewage age vs capacity considering the cloudy crystal ball the utility has.

At the end of the day, I think I don't see much of a difference in septicity between 5 hour old sewage (4" pipe) and 10 hour old sewage (6" pipe), but you double the capacity and stand a good change of not having to maintain 2 parallel lines (if a 2nd line is built) in perpetuity.

Anyway, good luck with this.