Parallel Pipe 2

Try the link below. It's based on the Hazen-Williams Equation.





Matt

The concepts of "Equivalent Pipe Dimaeters" or "Equivalent Number of Pipelines", and tables such as explained at least for nominal internal diameters on pages 17-10&11 and other pages at may be of at least some quick/approximate help to you for multiple lines. In other words/e.g., per Table No. 17-3 roughly two 18" pipes will have the same carrying capacity as one 24" pipe (and of course there are tables for flow and headloss through that one pipeline, such as Table No. 17-1). Once this is quickly established, I think actual headloss can perhaps then be checked with actual flows and more exact internal diameters etc.

Don't use Hazen Williams, unless you've got water, or have corrected the C term for your fluid.

Oh sorry, this IS the water dist forum.

Download Epanet. Free software. Run parallel pipes between two nodes.

Avoid Hazen Williams especially for large pipelines. Use Darcy Wiesbach

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

There have been (I believe now for decades) many available equations, procedures, tools, and now of course also fancy/slick computer etc. modeling software based on these and more approaches for determining head loss/pressure conditions etc. in pipelines. While I basically understand (and I guess essentially agree that from at least a purist standpoint) Darcy Wiesbach is in general at least theoretically better/more comprehensive than Hazen Williams, at this time I cannot/would not build a case that the Hazen Williams approach does not have utility, or that the hundreds or thousands of professional engineers and others who have used it over many decades/are using it now at least for water applications were/are wrong. I am aware that a notable paper, “Flow of Water in Pipelines” was even presented by Mr. A.M. Friend, an ASCE Fellow, at a conference in 1968 in San Diego, California and I suspect published in ASCE Proceedings that essentially compared many formulae approaches, including Hazen Williams and Darcy Wiesbach, looking at various formulae assumptions or plug-in parameters/values and also using some common water supply examples. This gentleman’s conclusions included, “The Hazen-Williams formula is satisfactory for hydraulic calculations of losses in the flow of water in pipes with proper attention to the value of the roughness coefficient within the limits of accuracy of all the factors involved.”
I noticed that some of Friend’s curves of velocity vs. friction loss per example length of pipeline in his paper now near 40 years ago (some comparing Hazen-Williams, Manning, Scobey, and Darcy, though even more approaches are talked about in his paper) laid quite nearly right on top of each other in a couple different pipe size examples he provided with sizes up to 24", particularly in 2-7 fps/1-2 m/s water flow ranges that I believe are quite common even to this day in water systems (it is thus quite possible most or all of these referenced engineers or scientists/technologists may have been quite competent, at least for their day!) Of course there are thousands of projects and maybe in aggregate hundreds of thousands miles/kilometers of pipelines designed with up to 24" sizes.
I guess I would only add that in my opinion the latter part of Mr. Friend’s quote above may be true of all equations – if you put good information into the left side of a sensible equation you can get good results on the right side, if you enter garbage on the left side you may well get garbage on the right!

You guys should really move to the Churchill equation. Works for all fluids, all diameters, laminar and turbulent flow and NO left side right side garbage or iterations required.

Hi rconner,

Whilst I respect your opinion and the work our forebears have performed there is evidnece out there that for large pipelines Darcy Weisbach is a more accurate approach. This is especially so if the fluid is not water.

Yes the horse and cart did transprot goods. But now we have semi trailers. No need to look back.

Many engineers use Hazen Williams as it is easy to write a spreadsheet algorithm than the recursive requirement of Darcy Weisbach. Just laziness really.

It seems civil engineers use HW and mechanical and chemical engineers DW formulas. perhaps the problem lies at the university professor's door.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

Even the pipefitters are using Churchill. Try it you'll never go back to HzW or DW.

I am not one to impugn/castigate or even accuse of laziness any "civil engineers" for use of the Hazen Williams approach, and certainly not without specific evidence that the work in the application they are performing is not up to snuff. While I don’t know about Australia, I believe this might be considered an affront of at least our local engineering ethics. I think there are many civil engineers involved in piping work for municipalities and utilities, as well as some civil engineering folks working for consulting firms, that are most heavily involved or specialize in water (the forum we are now in) and wastewater work, and for that matter even in this day and time predominantly not extremely large diameter pipe size jobs. I believe on the other hand many chemical etc. engineers work for plants/energy industries or refineries etc. that may well have many different types of fluid/gas process lines and also with hugely variable temperatures. Is it possible that their or their predecessors direct needs, experience and knowledge influences the tools they in general utilize to perform the jobs? While I think good engineers and scientists in general should try to be as precise as practical in their analyses or progress toward an answer, alas is it possible that (similar to variations in construction methods) there is more than one way to do engineering? If experience indicates the method in effect gives virtually the same result in the application (as it appears in the cases indicated by Friend), I’m not sure I could in all good conscience dictate the method to the practitioner. Of course I know also precise application of DW requires input/knowledge of? the temperature of the fluid to be conveyed. In some parts of our country, I believe fluid temperatures for example of some raw water supplies can fluctuate quite widely with seasonal variations – do you do your DW analyses/sizing etc. at near zero degrees C. encountered in the winter or the 30+ degrees C. encountered in the summer? Of course if one knows the actual temperatures, time can be spent analyzing per DW at either temperature or any compromises between same if anyone wants to, though of course this complexity is not present in the HW approach. Not saying this is the case in any specific application, but if the HW approach with the input values per the experience of the practitioner were to give a result equal to DW at a temperature somewhere in between, who has provided most cost effective engineering services to the Owner?
As far as application to very large size pipes, I suspect pipe size in general, and certainly any available laboratory work were generally some smaller in Hazen-Williams day as a result of populations served (we cannot blame them for this!) Arguably few things in any field stay exactly the same forever, and I believe there has in fact even been some evolution in recent decades of the HW approach, it would appear perhaps even anticipated by folks nearly as far back as Friend (see the last part of the quote I provided earlier). In this regard, I also noticed in a new book published by Haestad/Bentley, “Advanced Water Distribution Modeling and Management that there now are some at least slight adjustments advocated e.g. in the values suggested for friction coefficient C as the pipe sizes get very large – see “C-factor” table at (is it possible that this has probably been done as a result of what has been observed in subsequent/more contemporary research and/or field and/or laboratory results on larger pipelines?) Of course “Advanced…” hardly conjures up visions of the “horse and cart”!
As far as blaming “university professors” for the use of HW, I wouldn’t do that either. While I haven’t been sitting in a university classroom for awhile, I suspect many competent professors are at least exposing students to multiple methods, and I wouldn’t be surprised if they in general are even spending a great deal more time trying to teach inarguably more complex DW than they are HW, because as you’ve noted anyone who can look at readily available tables or correctly type/chain one formula into an Excel program, or who can input a few numbers/punch buttons on a scientific calculator (in the right sequence for the power functions to work, and in the right units etc.), can in effect thus use HW!

As I remember back in college
DW was taught as the gold standard,
there was a mild discussion of H-W in the text but the units were intentionally left out to prevent the students from using such an easy equation,
DW has a broader scope allowing different fluids, viscosity's and densities, but if you are using water at normal distribution temperatures, not many fittings, with flows exceeding laminar but not excessive velocities, use the simple solution, this then allows the expansion of the simple solution to the complex environment of a water distribution system with great accuracy, because any well built model will be calibrated to adjust the C value to the results of pressure measurements and flow tests

Hydrae