Hazen Williams Equation and Minor Losses

[CivilG]

I have a question concerning the Hazen Williams equation for determining Head Loss. Is there any way to figure minor losses such as the losses that occur at valves and fittings? Or does Hazen Williams only calculate major losses in pipes?

Thanks,

 

[ashtree]

HW only does major losses in pipes. There are plenty of other formulas for losses in valves and fittings.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[jgailla]

There are typically equivalent lengths for various valves and fittings. I think Crane has equivalent lengths.

 

[dbill74]

jgailla is correct, to account for valves, fittings, etc, you need to convert to equivalent length. I.E. a 90° elbow will have the same pressure drop as 3 - 13 feet of straight pipe depending on the diameter of the pipe. One source of equivalent lengths is www.engineeringtoolbox.com

 

[rconner]

For any newbies reading this thread now or in the future, the concept spelled out further of "equivalent length" as a way to handle minor losses( e.g. that due to head losses through fittings, valves etc a little higher than through the same laying length of straight pipe) is that when there is say, "L prime" distance station to station being analyzed, one in most rigorous form of the H-W approach should of course add up all those individual, extra "equivalent lengths" and plug the quantity into the equation, " L" (total or converted)= L prime + the total of all "equivalent lengths", with larger "L" thereafter into the Hazen-Williams equation to determine total head loss between stations.
That being said, I think the answer to this question (like so many others on these forums, as can probably be gleaned from some learned references in this field) is "it depends" i.e. on the designer, experience and intent. I think some designers ignore minor losses for at least some purposes, maybe with a little lesser value of "C" coefficient than if it were all straight pipe in a flow laboratory (knowing there could be a few fittings there, or added in construction to get around previously unknown obstacles in the field, and some also similarly do calculations for some purposes not necessarily with the actual inside diameters of various pipes but instead with simplification to "nominal" diameters for flow calculations.
In any case, I think rigor is in general good, and one area where one really should look very closely at minor losses and also size of pipe selected minor losses is probably in pump suction piping where head loss among other things is very critical to proper performance and efficiency, and there also might be a good many fittings, valves and specials etc. in relatively short lengths of pipe.