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  1. #1

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    Default driver/engineer math

    Hi guys, This is have kind of a weird request for my first post, but could you guys help me out with a quick refresher in the pump ops math. I have a d/e promotional test coming up in about 2 weeks(i just found out about it). I currently drive(acting d/e) now and have been state certified in florida for about 10 yrs. That is where the problem lies, I havent had to do the math since my state test. I have been talking to guys i work with and friends from other depts. but no one really remembers the math. I have all the formulas but i'll be damned if i can remember how to do them. I have a written, then if i pass it i move on tho the practical. The practical isnt what worries me, its the actual working out the math on paper that does. I look at it and its jibrish to me. Is there anyone that could spend a few minutes on the phone or online with me and point me in the right direction. I have searched here and google but i cant seem to come up with what i'm looking for. I looked for a local refresher course(nobody is offering one) and was also looking for an online refresher but cant seem to come up with anything there either. I know this is something i should have stayed up on, but the acting position has only been for a few months and the test was something i wasnt expecting to happen so soon. Thanks for your help.


  2. #2
    Forum Member CrnkB8's Avatar
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    You currently drive and act as d/e and don't know hydraulics? What are you doing now? Let me guess, someone told you "if we pull a line, just run the pump at ??? pressure" and you have no idea how they came up with that. Yea, this is something you should have stayed up on.

    Just throttle up until the crew complains and then back it down 5 psi.

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    Forum Member CrnkB8's Avatar
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    OK, here's the deal. The formula for friction loss is: FL=CQ²L.

    "C" is the coefficient," Q" is the quantity of gallons per minute divided by 100 and "L" is the length of the line divided by 100. Coefficients for hose are: 1½" = 24, 1¾" = 15.5, 2½" = 2, 3" = .8, 4" = .2 and 5" = .1

    Therefore, if we have 200' of 1¾" with a variable for nozzle set at 125 gpm the formula is: FL=15.5 x (1.25) ² x 2. Doing the math, 15.5 x 1.56 x 2 = 48 psi friction loss. It takes 100 psi to run a fog nozzle, therefore 100 psi + 48 psi = 148. This is the discharge pressure you should be pumping at.

    Another line, if we have 200' of 2½" with a variable for nozzle set at 250 gpm the formula is: FL=2 x (2.5) ² x 2. Doing the math, 2 x 6.25 x 2 = 25 psi friction loss. It takes 100 psi to run a fog nozzle, therefore 100 psi + 25 psi = 125. This is the discharge pressure you should be pumping at for this line.

    Let me know if you grasp this before we get into smooth bore nozzles. Because we need to figure out the gpm of the tip size before we can put it into the equation.

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    Quote Originally Posted by CrnkB8 View Post
    You currently drive and act as d/e and don't know hydraulics? What are you doing now? Let me guess, someone told you "if we pull a line, just run the pump at ??? pressure" and you have no idea how they came up with that. Yea, this is something you should have stayed up on.

    Just throttle up until the crew complains and then back it down 5 psi.


    thats not quite the case, however doing the "book" math for a written test is about 10 yrs behind me. Thats what i need to be refreshed on. Yes i am not afraid to admit i should have stayed up on the math but i didnt, i rode backwards up until this point and a year of medic school kind of got thrown in there too. I pump our trucks at rates that were predetermined before i was with this dept. and i works for us, but i want to be knowledgeable and proficient at this job, thats why i asked for help and i want to know it by the book so that i can be ready for anything that might be presented to me now or in the future. Anyone can pull levers and turn the throttle up or down but i dont want to be that guy.

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  6. #6
    Forum Member CrnkB8's Avatar
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    Got the concept yet for friction loss? Do we need to spend more time or proceed with figuring out GPM?

    PM me if you see the need.

  7. #7
    Forum Member CaptOldTimer's Avatar
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    Here is a simple pump operator’s pump pressure guideline.

    Ennie - Meanie - Moe, turn up the throttle, if it’s too much, they will let you know!!



    Beside, pi is round, cornbread are square!!
    Stay Safe and Well Out There....

    Always remembering 9-11-2001 and 343+ Brothers

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    Quote Originally Posted by alducks View Post
    interesting they suggest 80 psi for for fog nozzle handlines. On an automatic nozzle that can cause a massive loss in gpms on select gallonage nozzles there might only be a 5 to 10 gpm flow difference but the stream quality will suffer.

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    MembersZone Subscriber ffmedcbk1's Avatar
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    Quote Originally Posted by nameless View Post
    interesting they suggest 80 psi for for fog nozzle handlines. On an automatic nozzle that can cause a massive loss in gpms on select gallonage nozzles there might only be a 5 to 10 gpm flow difference but the stream quality will suffer.
    I also hope that they were rounding all there #'s to simplify when it came to sb flows.... but a 1 1/4" @ 50 is not 300 gpm
    Originally Posted by madden01
    "and everyone is encouraged to use Plain, Spelled Out English. I thought this was covered in NIMS training."

  10. #10
    Forum Member CrnkB8's Avatar
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    Quote Originally Posted by ffmedcbk1 View Post
    I also hope that they were rounding all there #'s to simplify when it came to sb flows.... but a 1 1/4" @ 50 is not 300 gpm
    They're close. It's actually 328 gpm.

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    MembersZone Subscriber ffmedcbk1's Avatar
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    Quote Originally Posted by CrnkB8 View Post
    They're close. It's actually 328 gpm.
    not too big of an issue but then it throws off the FL calcs. I believe the FL = 23ish per 100 feet.
    Last edited by ffmedcbk1; 08-19-2009 at 11:33 PM.
    Originally Posted by madden01
    "and everyone is encouraged to use Plain, Spelled Out English. I thought this was covered in NIMS training."

  12. #12
    Forum Member FF4606's Avatar
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    Your best bet for the test is to learn the hand method for the 1 3/4 and the 2 1/2. That will get you close enough in most cases for a multiple choice test. For the larger diameter stuff you will need to learn some of the math.

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    Forum Member CrnkB8's Avatar
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    Quote Originally Posted by ffmedcbk1 View Post
    not too big of an issue but then it throws off the FL calcs. I believe the FL = 27ish per 100 feet.
    Depends on whose formula you use. I come up with 22 psi per 100 feet with that size tip on a 2½

  14. #14
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    the values for hydraulics have slight variations depending on who you are talking to, bet to get the friction loss coefficients from the same source as the test. Same with the GPM for certain size tips and for fog nozzles. You don't want to mess yourself up over something small like that

  15. #15
    Forum Member CrnkB8's Avatar
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    Quote Originally Posted by nameless View Post
    the values for hydraulics have slight variations depending on who you are talking to, bet to get the friction loss coefficients from the same source as the test.
    True. Sometimes you can get the coefficients from the hose manufacturer. When in doubt, go by the department policy.

    Quote Originally Posted by nameless View Post
    Same with the GPM for certain size tips and for fog nozzles. You don't want to mess yourself up over something small like that
    Agreed. Some people can drive themselves nuts with friction loss and GPM. I use the formula GPM = 29.7 x D² x √P. Using the above example for an 1¼" smooth bore tip on a handline:

    GPM = 29.7 x 1.25² x √50

    29.7 x 1.56 x 7.07 = 327.56 (I rounded up to 328 gallons per minute)

  16. #16
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    A quick fire ground trick i learned that actually comes out to being accurate is a condensed Q for 2 1/2" is Q squared times 2, so Q=quantity, you have 200' of 2 1/2" flowing 200 GPM, your Q would be 2 squared= 4, multiply by 2 =8 P.S.I. per 100', so total loss is 16 P.S.I., hope that helps some

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