Advantages of Return Bends in Fire Sprinkler Systems

8/3/2016

Components of a Return Bend
A return bend is the piping arrangement for pendent sprinklers where piping stems from the top of the branch pipe (riser nipple), runs horizontally (arm over), and then down to the sprinkler (drop).

Components of a return bend in a fire sprinkler system

Where Required
Raw Water Sources, Mill Ponds, Open-Top Reservoirs

Required to avoid sediment and mineral deposit accumulation (NFPA 13 2002 Edition Section 8.14.18.1, 2007/2010 8.15.18.1, 2013/2016 8.15.19.1)

Dry Systems

Although in theory return bends would trap air and prevent water from traveling to a pendent sprinkler, in practice many installers have found water trapped at pendent sprinklers in dry systems even when on return bends. This is in part why return bends on dry systems as well as sprinklers are required to be located in heated areas. (NFPA 13 2002 7.4.1.4, 2007/2010/2013/2016 7.3.2.5)

Where Not Required
Deluge Systems

Deluge systems already provide an open orifice, so sediment accumulation to the extent that the system would be plugged is typically not a concern. (NFPA 13 2002 8.14.18.3, 2007/2010 8.15.18.3, 2013/2016 8.15.19.3)

Where Dry Pendent Sprinklers Are Used

Sediment accumulation may be less of an issue at the sprinkler, but could still be a concern at the edge of the dry shaft. (NFPA 13 2002 8.14.18.4, 2007/2010 8.15.18.4, 2013/2016 8.15.19.4)

Wet Pipe Where K-Factors are 11.2 or greater

In theory large orifices would be more difficult for accumulation of sediment to block. (NFPA 13 2013/2016 8.15.19.5)

Return bends are used primarily to prevent sediment accumulation in the drop to the sprinkler.

So Why Use Return Bends?
1. Sediment Accumulation

Prevent mineral deposit, pipe scale, and sediment accumulation (NFPA 13 2002 8.14.18.2, 2007/2010 8.15.18.2, 2013/2016 8.15.19.2)

2. Sprinkler Installation Flexibility

By piping from the top of the branch pipe instead of the side, sprinklers have the flexibility to be located at the center of tile or a specific location with greater tolerance for the sprinkler installer

3. Remodel and Shell Friendly

Where shell spaces are provided with upright sprinklers, return bends can typically be installed without modifying the branch piping
When systems undergo remodels, taping the top of the branch piping allows for flexibility in future sprinkler placement.

Use of return bends on outlets at the top of branch pipe makes relocation and exact-location placement easier for installers.

Things to Consider
Hangers

Hangers are required to prevent upward movement on the arm over piping when:
- the arm over is steel, exceeds 12 inches, and system pressure exceeds 100 psi (NFPA 13 2002/2007/2010/2013/2016 9.2.3.5.2)
- the arm over is steel and exceeds 24 inches (NFPA 13 2002/2007/2010/2013/2016 9.2.3.5)

Minimum Outlet Dimension

New systems require outlets to be minimum 1-inch, but can have temporary bushings serving upright sprinklers (NFPA 13 2002 8.14.19.1, 2007/2010 8.15.19.1, 2013/2016 8.15.20.1)

Minimum Riser Dimension on Existing Systems

For hydraulically designed systems, nipples less than 1 inch are allowed but cannot exceed 4 inches in length, and must be incorporated in hydraulic calculations (NFPA 13 2002 8.14.19.4, 2007/2010 8.15.19.5, 2013/2016 8.15.20.5)
For pipe schedule systems, nipples less than 1 inch are allowed but also cannot exceed 4 inches in length (NFPA 13 2002 8.14.19.3, 2007/2010 8.15.19.4, 2013/2016 8.15.20.4)

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Further Reading
Minnesota Public safety Issue | Link
NFPA 13 | Link

A guy

8/5/2016 11:44:22 am

Nice pictures. You should make more.

Janet A. Washburn, CFPS, FM, MIFireE, MS

8/6/2016 07:17:11 am

Excellent article and I appreciate the time spent with the code references! The pictures are very helpful. I just shared this article with hundreds of peers in Florida.

Joe Meyer link

8/8/2016 08:19:38 am

Thank you both for the feedback and for spreading the word! I am looking forward to future visuals on interesting topics and lessons learned.

Vincent Boves link

12/2/2016 06:00:14 pm

Your drawings rock, love to see more.

Dustin

5/11/2017 08:19:00 am

The exact references to the NFPA codes are very helpful. Great stuff!

Stephen Shishko

6/12/2017 06:15:37 pm

Thank you very much. I have just started to do sprinkler shop drawings and this made it very clear why concealed heads are installed on return bends

Kylie Dotts link

7/5/2017 03:34:00 pm

I like how you said that this kind of fire sprinklers prevent mineral deposit. With how important a fire sprinkler system is you definitely do not want something like a hard water deposit blocking the flow of water during an emergency. Getting a system that will allow you to do minimum upkeep and maintenance will also help you save time and money, allowing you to focus on your business.

De Soto

1/20/2018 08:59:55 am

When flex drops replace hard-piped return bends, how are they commonly installed--- coming out from the top of the pipe, side or bottom?

JOE MEYER

2/17/2018 05:47:41 am

In general, flexible drops can be installed from any direction; however, side tapping or tapping from the top of the branch pipe does prevent sediment accumulation just as the return bend does.

There's an article covering flexible drops and their considerations here that might help, too: https://www.meyerfire.com/blog/considerations-with-flexible-sprinkler-drops

arthur

2/6/2018 08:55:09 am

Is it necessary to connect the branch from the top of the mains with a spool or can direct branches be taken from the side when clean water sources are used.

What are the advantages and disadvantages by using either method and why???

Are there any unsaid regulations or thumb rules followed regarding this issue?

JOE MEYER link

2/17/2018 05:52:52 am

I see branch lines connected directly to to the sides of mains all the time in clean(er) water situations. Mains typically have caps at the end of the pipe for inspection and potential flushing in part to help clear deposits if there are any.

The height of the main relative to the branch lines can become important in obstructed situations with joists and beams to run the branch lines higher in beam pockets while keeping the main below the lowest beam or girders. Lower mains can also help the system drain if it's not installed perfectly level for wet systems, while dry systems the mains are typically lower than the branch lines to allow for proper sloping.

Joe Sprinklers

4/20/2018 01:13:06 pm

Hey, what to do if outlet is 1/2" with upright directly on outlet, how you arm over theN???

Joe Meyer

10/9/2018 07:11:17 am

There are "street elbows" that have a male 1/2" thread to a female 1" outlet. Just be careful as these are typically only allowed in retrofits and they must be hydraulically calculated. NFPA 13 addresses these in more detail.

Fecmolac

4/24/2018 02:52:44 am

The is any minimum requirement for the length of the drop without support. Sometimes we came across the installation where sprinkler drop more than 2 mtrs without support. I am looking for the support requirement for the drop.

ALEJANDRO

6/14/2018 11:33:10 am

When offices are reconditioned, what parts of the sprinkler system can be reinstalled.

GREETINGS OF MEXICO

Jay

9/27/2018 04:41:21 am

We connect our branch line below the cross main pipe due to the structure beam. If we lower the cross main, the pipe will be exposed below the ceiling so we connect it that way. NFPA 13 only specify that sprinkler should have return bends and should be connected on the top of the branch pipe ,but im not sure if the branch pipe should be connected on the top of the cross main. Please enlighten me on this issue. Thank you so much

Please forgive my English.

10/9/2018 07:10:01 am

Branch pipe is typically run at the same level or above the main so that the system can be drained.

Fundamentally, there's no major reason why branch pipe can't be run below a main, but it'll be difficult to drain down the system entirely because someone will have to drain each individual branch pipe.

JAY

10/12/2018 04:43:15 am

Mr. Meyer, thank you so much for answering my question.

So is it necessary to drain the sprinkler system? In what case we need to drain it?

10/12/2018 07:01:38 am

It may not be in the short term, but draining the system will be necessary to fix any leaks, make any changes to the system, or to inspect the pipe interior.

Dave Anderson link

1/18/2019 05:08:10 pm

That is a good point that you should use return bends to prevent mineral deposits from happening. It would be good for a fire sprinkler not to have sediment accumulation. That way when there is a fire, the sprinklers won't malfunction.

nidhin kumar

4/6/2019 02:45:48 am

simply superb explanation....

Craig Brown link

4/22/2020 04:14:06 pm

Is there any reference out there about the maximum length of the horizontal section of a return bend / arm-over? I don't see one in NFPA 13, but may be missing it. Reason to ask, have an installation where the pendent sprinkler is attached to a ~6-ft long arm-over

Regards

CAB

4/23/2020 07:13:30 am

Hi Craig,

There is not a limit to armover length, but if it is in the remote area it would need to be accounted for in hydraulic calculations.

That being said, long armovers (over 1-ft for 100 psi or higher systems or over 2-ft for systems under 100 psi) require at least one hanger. If the armover is exceptionally long, it may require more.

Hope this helps! Joe

Kavman

6/17/2020 01:45:35 am

Hi Joe Meyer,

It is wonderful explanation on return bend requirements. Is there any maximum drop limitation without any support to Pendent sprinkler in common cross main for both Pendent and Upright sprinklers as per NFPA .

6/23/2020 05:12:36 am

Kavman,

Sprigs are pretty straight forward - generally if they're 4-ft or over in length then they need additional support.

For pendents, there was a recent good discussion on it here: https://www.meyerfire.com/daily/correct-way-to-support-long-sprinkler-drop

Check out that link and it may give the guidance you're looking for. Thanks!

Comments are closed.

Advantages of Return Bends in Fire Sprinkler Systems

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