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Return bend requirements according to NFPA 13

Return Bend Requirements According to NFPA 13 - 2019 Edition

Return bend requirements according to NFPA 13 - 2019 edition

Return bend requirements according to NFPA 13 - 2019 edition



When return bend is required?

  • Return bends shall be used where pendent sprinklers are supplied from a raw water source, a mill pond, or open-top reservoirs.


Where return bend is not required?

  • Return bends shall not be required for deluge systems.
  • Return bends shall not be required where dry pendent sprinklers are used.
  • Return bends shall not be required for wet pipe systems where sprinklers with a nominal K-factor of K-11.2 or larger are used.


What are the advantages of using return bend?

  • Return bends are used basically to avoid accumulation of sediment in the drop nipples so, it shall be connected to the top of branch lines in accordance with figure below.

Return bend requirements according to NFPA 13 - 2019 edition

Return bend requirements according to NFPA 13 - 2019 edition



What are the Components of return bend?


1- Arm over: A horizontal pipe that extends from the branch line to a single sprinkler or a sprinkler above and below a ceiling.

2- Riser nipple: A vertical pipe between the cross main and branch line.

3- Branch line: The pipes supplying sprinklers, either directly or through sprigs, drops, return bends, or arm-overs.

4- Hanger: A device or assembly used to support the gravity load of the system piping.

5- Pendant sprinkler: A sprinkler designed to be installed in such a way that the water stream is directed downward against the deflector.


Design Tips:

  • For new systems, outlet size shall be minimum of 1 in and we can use hexagonal bushings to accommodate sprinklers  attached directly to branch line fittings to allow for future system modifications.

  • For existing systems (pipe schedule) riser nipples less than 1" are allowed but shall not exceed 10 cm in length.

  • For existing systems (Hydraulically calculated) riser nipples less than 1" are allowed but shall not exceed 10 cm in length, and shall be considered in hydraulic calculations.

  • Arm over shall be supported by hanger when its length exceeds 61 cm.

  • Arm over shall be supported by hanger when its length exceeds 35 cm and system pressure exceeds 100 psi.


References of this article:

- NFPA 13 - 2019 edition (Standard for the Installation of Sprinkler Systems)

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3 comments:

  1. NFPA 13 :what is the maximum length allowed while connecting Branch lines from cross main? any standard reference?

    ReplyDelete
  2. Thanks for all good efforts,
    If you add the clause no of NFPA will be appretiated.

    ReplyDelete