Fitting Equivalent Lengths and Internal Sizes
The equivalent lengths of fittings (except user defined fittings) are stored in the program. These lengths depend on the sprinkler code selected for the particular pipe. The values are primarily those specified in AS 2118, NFPA, NZS 4541 and SSCP52, however for quite a number of fittings, data from other sources (where this is allowed by the particular code) are included and these sources are indicated in the extreme right hand column of the tables by a 'source' the legend for which is on each table.
Because the pressure loss in pipe fittings is primarily a dynamic loss i.e. there is very little loss due to friction, the pressure loss (in kPa or p.s.i) of a particular (nominal size) fitting will not vary significantly when installed in a pipe with the same nominal diameter but a slightly different internal diameter. Therefore the equivalent length must be modified to keep the pressure drop the same. If the Hazen Williams coefficient for the fitting and the pipe are not the same, a correction for this must also be made.
If a fitting is installed in a pipe of different internal diameter or Hazen Williams Coefficient the equivalent lengths must be adjusted to give the same total pressure loss using the following formula:
ELCALCULATED = ELTABLE x (D1/D2) 4.87 X (C1/C2)1.85 eqn B-01
Where:
D1 = the internal diameter of the pipe, the fitting is installed in.
D2 = the internal diameter of the pipe that the stated equivalent length is based upon
(see table below)
C1 = the Hazen Williams coefficient of the pipe the fitting is installed in.
C2 = the Hazen Williams coefficient of the pipe that the stated equivalent length is based on.
The fittings with equivalent lengths stored in the program and the pipe material and Hazen Williams coefficient that they are assumed to be based on are:
Fittings Base Pipe Material Base HW Coefficient
| ### Fittings | ### Base Pipe Material | ### Base HW Coefficient |
| Screwed (steel) | NFPA -Schedule 40 Steel (AS40) | 120 |
| Other codes – AS1074 & BS1387(ASAM) | 120 | |
| Valves, etc. (steel) | NFPA -Schedule 40 Steel (AS40) | 120 |
| Other codes – AS1074 & BS1387(ASAM) | 120 | |
| Flanged or socketed | All codes – American Unlined Cast Ductile Iron | 100 |
NFPA Fittings - SE, TT, etc
The equivalent lengths listed in NFPA are for fittings when installed in Schedule 40 steel pipe.
When installed in Steel and Unlined Cast Iron Pipes eqn B-01 applies with:
D2 = the internal diameter of the shedule 40 steel pipe.
C2 = 120
When installed in all other pipes (including lined Cast Iron, Copper, CPVC, and user defined pipe materials.) no diameter correction is made to the screwed steel fittings (SE, TT, etc) or the gate valves and check valves because, strictly speaking, these fittings (and their equivalent lengths) do not apply for these other pipe materials. In the absence however, of any other readily available data they can be taken as an approximation. That is, it can be assumed, for example, that the equivalent length of a steel screwed elbow in an AS40 steel pipe is approximately the same as for a copper elbow in a copper pipe.
The Hazen Williams correction of (Cpipe/CBASE)1.85 is however made, where Cpipe is the Hazen Williams coefficient for the pipe and CBASE is the base Hazen Williams coefficient from the table above.
The diameter correction is applied by the program for NFPA to all steel fittings except NFPA13D steel fittings.
AS2118, NZS4541 and SSCP52 Fittings – SE, TT, etc.
In the other codes the program applies the same correction for screwed steel fittings but using the diameter of Australian Medium Steel in lieu of Schedule 40 for D2, up to 150mm.
In all other pipes only the Hazen Williams correction is made.
Flanged or Socket Fittings (E1 to C4)
The basis of the equivalent lengths for these fittings cannot be confirmed so it is assumed they are based on American unlined Cast Iron pipe diameters and a Hazen Williams coefficient of 100.
In Steel Pipes
When installed in steel pipes eqn B-01 applies with:
D2 = the internal diameter of American unlined cast iron pipe (this data originating from the USA).
C2 = 100
For SSCPP52 C.I. no diameter correction is made and C2 = 120 (lined cast iron pipe)
In Unlined Cast Iron Pipes
In unlined cast iron pipes no diameter correction is made , only the Hazen Williams correction is applied using eqn B-01
In all other Pipes
When installed in all other pipes (including lined Cast Iron, Copper, CPVC etc.) it is again assumed that the fitting diameter is the same as the pipe and only the Hazen Williams correction is made.
For SSCP52 C.I. Cement Lined fittings the appropriate values from this code are used with no diameter correction applied, but a H\&W Correction is made based on C2 = 120.
Note that although the diameter correction above is made for screwed, flanged or socketed fittings in both steel and cast ductile iron pipes it is recommended that the user gives careful thought to the validity of using screwed fittings with ductile iron pipes and flanged or socketed fittings with steel pipes. The entry of copper or PVC fittings with steel or ductile iron pipes or steel or ductile iron fittings with copper or PVC pipes should be treated with caution as this may compromise the accuracy of the results.
User Defined Fittings
If any other fitting type is required to be used (e.g. a lined ductile iron fitting) the above correction does not apply and the user must enter the equivalent lengths as User Defined Fittings.
When entering this data the user can also select the material code and the HW Coefficient that this data is based on. The program will then apply the above diameter & HW Coefficient corrections. For example, if the user has data for cast iron cement lined fittings (as distinct from unlined fittings) then this would be entered with a pipe code of say C150 or if the user has entered their own pipe diameter data, the code for this can be entered. However if the base pipe material code is entered as NONE then the fitting equivalent lengths will be taken as the same no matter which pipe material is being used. Hence the fitting pressure loss will not be fixed & will be a function of the internal diameter of the pipe it is installed in.
Note again however that the inclusion of user defined fittings in pipes of a material other than that on which the fitting equivalent lengths are based upon, should be avoided or at least given careful thought.
The uncorrected equivalent lengths used by the program are as listed in the following tables:
For NFPA Commercial
For NFPA13D
For GB50084
For CPVC
For NFPA750
For AS4587
For all HDPE Pipes
For all Stainless Steel Tubing
Values of equivalent length in the tables with an asterisk are interpolated values.