1. #1
    STBURNE
    Firehouse.com Guest

    Post Hose Size Coefficients

    What are some hose size coefficients that ya'll are experiencing? The textbooks say 1 3/4"=15.5, manufacturers claim lower coefficients. Flow testing indicates as low as 12 on some brands of 1 3/4" hose. What are your experiences?

  2. #2
    Truckie from Missouri
    Firehouse.com Guest

    Post

    I've noticed the same things. THese are what I've found, using pitot gages and the standard formulas: GPM=(29.83)(0.97)(D^2)(sq. rt. of NP) & FL=(C)(Q^2)(Hose length/100) In both cases (Q^2) is Volume/100, squared. The nozzle pressures we used were 50psi (sq. rt. = 7.07) for handline and 80psi (sq. rt. = 8.08) for master stream.

    1&3/4" -- 12
    2" -- 8
    2&1/2" -- 2
    4" -- 0.8
    5" -- 0.02

    Hope it helps.

    ------------------
    Proud Member of IAFF Local 3133!

    Stay safe.

    Ken

    ***DISCLAIMER***
    All postings I have &/or will post are strictly my opinions. I am representing only myself here, not the IAFF, Local 3133, or my employer. No animals were/will be harmed from the production of this disclaimer. Thank you.
    ***END OF DISCLAIMER***

    [This message has been edited by Truckie from Missouri (edited January 23, 2000).]

  3. #3
    Dalmation90
    Firehouse.com Guest

    Cool

    Glad to see someone actually doing the math back to find the actual coefficients!

    There is tremendous differences between fire hose -- especially the material of the liner, and if the hose expands when charged or not.

    A perfect example is Angus Hi-Vol. Angus' nominal 4" and 5" hose expands to 4.2" and 5.2" respectively. That's how they beat their competitors friction loss for the same size hose -- the Angus actually is a larger diameter when in use! So the standard coefficient for 5" is too high for Hi-Vol.

    Another new development is using a polyethleyene liner that's impregnated into the fabric instead of the traditional rubber liner -- apparantley lower friction, and slight increase in the inside diameter since the poly needs less space than rubber liners. Together, they both work to reduce the coefficient. (Plus it's noticably lighter than rubber lined hose!)

    Matt

  4. #4
    FyredUp
    Firehouse.com Guest

    Post

    The best way to determine friction loss charecteristics for your particular hose is through flow tests using inline pressure gauges and flow meters. Friction loss can vary widely between manufacturers.

    [This message has been edited by FyredUp (edited January 21, 2000).]

  5. #5
    STBURNE
    Firehouse.com Guest

    Post

    Thanks guys!

    The formula 29.83*c*d^2*square root of NP
    is the Hazen Williams formula, correct?

    Where did 29.7*d^2*square root of NP come from?

    Also, Truckie, what brand hose where you using?

    [This message has been edited by STBURNE (edited January 24, 2000).]

  6. #6
    e33
    Firehouse.com Guest

    Lightbulb

    hop to www.fofd.org/engineer.html and play with the engineers calculators, you can try all kinds of neat stuff. I happened upon it looking for similar info one day. God luck

    ------------------
    The opinions and views expressed herin are solely mine and not on the behalf of any department or organization I belong to.



  7. #7
    KEA
    Firehouse.com Guest

    Post

    STBURNE:
    >Where did 29.7*d^2*square root of NP come from>

    You will find it in the 18th edition of the NFPA Fire Protection Handbook

    Kirk Allen
    First Strike Technologies, Inc.

  8. #8
    STBURNE
    Firehouse.com Guest

    Post

    KEA-Why the different formulas?

    29.83*c*d^2*square root NP(Hazen Williams)

    versus

    29.7*d^2*square root NP (NFPA & IFSTA)

    Thanks for the web site e33!

  9. #9
    Truckie from Missouri
    Firehouse.com Guest

    Question

    To be honest, I don't know what brands of hose we are using. Some are rubber lined double jacket, some are lightweight w/ no rubber lining--they have some kind of liner impregnated on the inside of the jacket. It all works well for us.

    As for the question of why two formulas? I have no asnwer accept that the formula seems to be ever so slightly different every time I take a hydraulics class... and the range had been from 29.7 to 29.9; most common one is 29.83 (at least in the classes I have taken).

    ------------------
    Proud Member of IAFF Local 3133!

    Stay safe.

    Ken

    ***DISCLAIMER***
    All postings I have &/or will post are strictly my opinions. I am representing only myself here, not the IAFF, Local 3133, or my employer. No animals were/will be harmed from the production of this disclaimer. Thank you.
    ***END OF DISCLAIMER***

  10. #10
    MembersZone Subscriber

    Join Date
    Dec 2007
    Posts
    19

    Default

    My department recently did coefficient testing on our primary attack hose and came up with coefficients of 11.65 for 1 3/4 and 1.33 for 2 1/2. The coefficients for the 1 3/4 were about 10-15% lower than our current standard of 2Q2+Q, but the coefficients for 2 1/2 resulted in friction loss of 30-40% lower. We are in the process of changing Friction loss calculation to CQ2L and this was the logical first step.

  11. #11
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    Default Flow and friction loss calculations

    The above mentioned formula is not the "Hazen-Williams Formula". The 29.87 d squared times squre root of p is the formula for flow from a circular opening. d = nozzle diameter p = nozzle pressure in psi The referenced "c" is really a butt coefficient that concerns the shape of the waterway directly ahead of the opening. A master stream device with the proper stream shaper is usually listed at 0.97 value for c, while a good quality hydrant can have a butt coefficient of 0.9. Poorly installed or improper hydrant connections that jut into the hydrant barrel may have values for "c" as low as 0.7. Doing a calculation for a 2" master stream, this formula calculates the flow 29.87 * 2 * 2 * sq rt of 80 to a flow of 1068 gpm without the "c" and a flow of 1037 using the value of cas 0.97

    The Hazen-Williams is in the general form of (K * Q * Q * L)/ D to the 5th power.
    Where: Q is flow in 100's of gpm - L is the number of 100 ft. joints of hose - D is inside hose diameter & K is an arbitrary coefficient that includes surface roughness, liner material, but is generally around 230 to 250 for double jacket, rubber lined hose. Generally 3" hose with 2 1/2" couplings has a friction loss equal to the flow in 100's squared, or a loss of 25 psi / 100 ft. at a flow of 500 gpm. If we use a K value of 243 and do the calculations for 100 ft. of 3" hose - we get 243 * 5 * 5 * 1 / 3 * 3 * 3 * 3 * 3 or 243 * 25 / 243 = 25 psi per 100 ft.

    The rub comes in when the manufacturer weaves hose so that stretches under pressure. Get a hand calculator and do the above exercise using 5" hose at 1000 gpm. That is 243 * 10 * 10 * 1 / 5 * 5 * 5 * 5 * 5 and compare it with published friction loss tables for 5" hose from various manufacturers. Finally do the same thing, but allow the hose to expand by 10% under pressure. That is a hose diameter of 5 1/2" instead of the 5" used in the second example. I think this will give a better feel for what happens when the LDH expands under use, and also why similar layouts yield different practical results under different pressure conditions.

    Hope this explains more than confuses.

    Kuh Shise - Just an old German B.S. er

  12. #12
    MembersZone Subscriber

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    Default

    If we could revive dead people as well as some can revive dead threads, maybe we'd be the highest paid profession in this country.

    Almost 8 years old, nice work!

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