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Head loss

  1. Jun 21, 2006 #1
    I was reading on this page...

    http://www.cda.org.uk/megab2/build/pub125/sec4.htm#5.1 [Broken]

    ...and I tried calculating head loss using both the forumla given, and the nomogram. Aren't these supposed to give the same result? Or am I missing something fundemental? Because they don't equal each other by a long shot...

    An explanation would be very much appreciated :-)
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jun 21, 2006 #2


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    Staff: Mentor

    What data are you plugging in?
  4. Jun 21, 2006 #3


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    Science Advisor

    The nomograms will be made from the equations for head loss. Unless a type-o was made in the webpage, they should coincide pretty closely. Are you sure you don't have a units snafu somewhere?
  5. Jun 21, 2006 #4
    I got them pretty much equal now, don't even know what must have gone wrong before. Damn units...

    One more question for you guys:

    I often see in literature that head loss is often set to 100 Pa/m pipe, at least for pipes bigger than 15 mm without further calculations, but almost all of my calculations show much higher values than this. Any idea why?
  6. Jun 22, 2006 #5


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    To my knowledge, a number like that is a design parameter (rule of thumb) developed after a lot of experience. It is a target to shoot for, not an absolute. This would help calculate the pipe diameter.

    I really can't imagine someone saying that "well, my pipe size is over 15mm. I guess my pressure loss will be 100 Pa/m no matter what I am doing." That just doesn't make much sense.
  7. Jun 26, 2006 #6
    The average losses should depend on an assumed pipe TYPE. Each type should have a different average loss coefficient.
  8. Jun 27, 2006 #7


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    Average loss coefficient? What is that? The only factor that would depend on the type of pipe is the friction factor. And then most people assume a smooth pipe on the first go around anyways.
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