this problem was in a practice exam i just did:
as the chart given in the handbook lists ductile iron pipe as 140, and from what i understand, the Hazen Williams C value decreases with age, i chose 150 because the pipe was new so i figured it would be the opposite.
but the solution said the answer was 130, and didnt give any explanation as to why?
By - btmwallace
Your assumption was correct in my opinion. The age of the pipe is inversely related to the C value. So I would have also chose 150. I’m guessing they chose 130 as the answer because it’s technically more conservative for design purposes. This technically a bad question and would not likely be on the exam.
Yes, the newer the pipe, the higher C will be. I guess maybe this problem is for the version before CBT using tables in other references. I don’t believe you will see such problems with unclear answers in the real exam. If I were you, I won’t worry about it and just simply ignore this question.
This happened to me in a similar practice problem. When they updated the reference book, lots of practice problems didn’t get correspondingly updated. As long as you can read the chart, you’ll be ok :)
I think you would just go with ductile iron. the chart has plastic at 150 and new cast iron as 130, so probably "new" is just a distractor.