1. #1
    Sand Creek Lynn
    Firehouse.com Guest

    Question Friction loss question. Theory and reality. Similar?

    I'm putting together a tanker filling system using a 1500 gpm pump that I'm about to buy.
    Pump is high volume [obviously] but quite low pressure. According to the performance curve it goes to 0 gpm at about 80 psi. So I'm interested in keeping the pressure extremely low. Will draft with 6 in. and fill with 5 in. ldh. Through 4 in. storz fittings. 4 in. because all our mutual aid uses 4 in. I'll be ok on my pressure using 50 feet of 5 in. through a 5 in. gate valve and the 4in. storz.
    So anyway I called Akron and an engineer there said when going through a restriction there is no noticible pressure loss if the length of the restriction is less than 2.5 times the diameter of the restriction.

    Example: 2.5 in. valve. If less than 6.25 in. long [2.5 X 2.5] I will have no noticible loss.

    So.... theoretically I could hook my 5in. line to a 2.5 in. fill valve on the back of my tanker and flow 1500 gpm though it without excess pressure loss. I'm not going to but the theory presents an interesting thing to contemplate.

    My question: in theory this would work.
    Has anyone played with something like this to see if theory and reality are similar?

    Thanks, Lynn.

  2. #2
    Firehouse.com Guest


    *If* it's just a 6" length of 2.5" you shouldn't have a problem.

    Friction loss isn't dependent on pressure -- it depends on the size of the pipe and how much volume you shove through it. I did three calculations here for 2.5"
    6" length loses 2psi to friction
    1' length loses 5psi to friction
    2' length loses 9psi to friction

    (OK, I used the coefficient for fire hose...iron pipe will be a tiny bit different)

    So as long as you deliver the water with just enough pressure to make through the last restriction, you're OK.

    The reason I did three calcs is this -- if it's only a 6" 2.5" and emptys directly into the tank, it only takes 2psi to push 1500gpm throuh it. Now if that fill has more pipe you can't see inside the tank, or even worse starts having 45 or heaven forbid 90 degree elbows in it, the FL starts to increase with length and bends.

    Let's run this scenario:
    Pump 1500gpm@50psi (I'm assuming...)
    200' of 5" to the wye = 36psi
    5" wye = 2psi (just a number, probably close)
    50' of 5" to the truck = 9psi
    5" to 4" Storz adapter = negligble
    36+2+9 = 47psi...
    That means from the original 50psi, we only have 3 psi left...that's the max friction for the fill to the tank...any more and you have to reduce flow to reduce the FL in the system.

    *Now* my standard disclaimer on 5" hose -- these figures are using the industry standard for 5"...some hose like the Angus Hi-Vol we use is actually 5.2" and has a lower FL.

    Friction Loss is FLOW dependent. Take the hose/wyes/adapters you plan to use. Flow 1500gpm through them, and take the difference in pump pressure and pitot pressure at the discarge to get the actual friction loss in "real life" for that setup. Doesn't matter if you pump 1500gpm @ 150psi or 50psi, you'll still lose the same difference between pump and discharge.

    If you have Microsoft Excel 95/97/2000 you can go to my website at www.mortlake.org and in the right hand top corner box there's a link to FireInfo Calculator Spreadsheet...it may take a minute to figure out, but it can do most of the common hydraulic calcuations.


  3. #3
    Firehouse.com Guest


    Actually, the loss is 8 psi at 1500 gpm. 2 1/2" open bore to flow 1500 gpm will have a NP, (a loss) of 8 psi plus any FL in the pipe and urbance loss of 15% or more in flow.

  4. #4
    Firehouse.com Guest

    Thumbs up

    If you would like to try your own eazy test,
    put a 2.5 X 5" storz on a discharge of your engine and the otherend with adapter to a deckgun. Check the flow with a guage.
    you will be surprised.

    [This message has been edited by wv-engineer (edited April 03, 2000).]

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