Definition of Branchline vs Cross mains

[doingwhat]

Our concern is the that every time we branch off from a primary branchline to pick two or three heads in small rooms the preceding branchline will be viewed as a cross main and then would have to be seismically braced regardless of size. If I only use all 1" to 1-1/2" CPVC for a small 13R project and both 1" & 1-1/2" pipe are supplying the sprinklers directly, so do i still to brace the cpvc pipe or i only need restraint when the pipe is less than 2-1/2"?

3.5.4 Branch Lines. The pipes supplying sprinklers, either directly or through sprigs, drops, return bends, or arm-overs
3.5.5 Cross Mains. The pipes supplying the branch lines, either directly or through riser nipples.
3.5.6. Feed Mains. The pipes supplying cross mains, either directly or through risers.

 

[doingwhat]

https://files.engineering.com/getfile.aspx?folder=b17c0583-7c8b-4fda-b355-69b357c8cb1f&file=a.jpg

 

[SprinklerDesigner2]

Except for hangers I don't think it matters like it used to.

 

[doingwhat]

do you mean i have to install bracing for the cpvc pipe regardless of the size?

 

[TravisMack]

If the piping is defined as a main per NFPA 13, Chap 3 then yes. You do bracing regardless of size. So if you have a 1" CPVC cross main, you will need to brace that cross main.

The question you need to resolve is if you have a branch line or a cross main. I think as you describe the primary and secondary are branch lines. But I don't have a view of it, just a description as I am "picturing" what you have.


Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[doingwhat]

so this is the floor plan. all pipe are cpvc.

 

[TravisMack]

So what are mains and what are lines in your plan? Note the definition of main, branch line and arm over. They will come in to play in your project.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[UFT12]

The loop piping seems to satisfy both the definitions of cross mains and branch lines. It does supply individual branch lines and it does supply sprinklers directly (or through sprigs, not visible in your drawing). However, since it is at least a cross main and branch lines are depended on it, per code and per common sense I would say bracing is needed. Also the right (vertical) side of the loop piping seems it does not supply any sprinklers directly so it makes a bit easier to understand the necessity of bracing.

On a side note, it may be worth it to discuss with your jurisdiction whether it is needed or not since plastic piping and of that size are typically flexible to handle earthquake loads (although their fittings may not). That would make more sense if the design loads in the project area are low. They may advice how other installations are made in the area of your project.

 

[doingwhat]

i can easily move some heads to the 1-1/2" pipe to make them meet the definition of branch line.

 

[UFT12]

In regards to bracing only, wouldn't be better to skip the looped pipe all together and just make it a tree system? One main that remains a main only with a couple of braces while all other branch lines supply the sprinklers. I doubt the densities we are talking here mandate a loop configuration. Just a thought for consideration.