Equivalent Length
The use of equivalent lengths is supported by AFT Fathom. This option is hidden by default, but can be enabled in Analysis Setup on the Junction Loss Models panel. After enabling this feature the properties windows for the bend and valve junctions will have another type of loss model called "Equivalent Length". In the pipe properties window the table in the fittings & losses tab will change as well. The options for bend and valve types come from table 23.4.3.1.1 in NFPA 13NFPA 13, Installation of Sprinkler Systems, 1999 Edition, page 13139.. If you are not using the NFPA 13 standard then using a user specified
The loss factors in table 23.4.3.1.1 assume that a HazenWilliams Cfactor of 120 and schedule 40 steel piping are being used. If your reference pipe is defined using a different HazenWilliams factor or different pipe schedule, then the equivalent length will be adjusted by equation 6.2 (Equation 1 below) on page 103 of Brock, Pat D. 2012Brock, Pat D., Fire Protection Hydraulics and Water Supply Analysis, Third Edition, Fire Protection Publications Oklahoma State University, Copyright 2012 by the Board of Regents, Oklahoma State University..

(1) 
Where:

L_{eq} = new equivalent length

L_{1} = original length

D_{eq} = diameter of new equivalent length

D_{1} = original diameter

C_{eq} = CFactor for new equivalent length

C_{1} = original Cfactor
This equation is intended for taking an equivalent length and adjusting for a new equivalent length based off changes to diameter and CFactor. This is a general equation, but NFPA table data from table 23.4.3.1.1 is only for schedule 40 steel and a CFactor of 120. Therefore the adjusted equivalent length can be written as shown in Equation 2.

(2) 
Equation 2 (adjusted from Brock et. al. Equation 6.2) will predict an adjusted equivalent length that coincides with the NFPA 13 equivalent length modifier 23.4.3.1.3.1 and the CValue Multiplier from table 23.4.3.2.1. Note that if the reference piping is using a friction model other than HazenWilliamsC_{eq} is assumed to be 120 and the equivalent length will not be adjusted due to friction.
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