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Calculating engine pressure

Discussion in 'Firefighter/EMS Talk' started by lomfs24, Jun 24, 2006.

  1. lomfs24

    lomfs24

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    I am trying to find a formula that will give me engine pressure. And I am actually looking for one that that is kind of a quick and dirty one that is maybe not 100% accurate but will get you in the ball park. Kind of like the 2AM rule in EMS to convert lbs to kg. The one's I have found give you long complex formulas that would take me a week to sit down and work through.

    What does everyone here use to calculate engine pressure as you are pulling up on scene?
    I know you can buy fancy calculators that do it for you. I know you can get slide rules etc... but what do you do if you don't have them? You know, when the calculator gets stepped on and the slide rule falls down the storm grate.
     
  2. faceplant

    faceplant

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    Why not do the calculations for your particular equipment then make your own chart to carry with you in your pocket or on the rig? We have SOPs that give starting pressures for each of the preconnects we use and a cheat sheet for changes. There are rules of thumb but I find a simple chart to be easier for me.
     

  3. FirNaTine

    FirNaTine

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    Know your preconnects and nozzles.

    I know for example that every 1 3/4" nozzle in my county is a 75 psi fixed gallonage fog nozzle. Now most hose loads are 150' or 200' and our training academy actually flow tested those loads and found that 150 psi engine pressure will provide at least 200 gpm to both lengths.

    If I pump a line at 150 psi the firefighter on the nozzle has the option to gate back if he does not need 200 gpm, but if I pump lower pressures to be "nice" and they need more it takes time to get on the radio and ask for it.

    If you cant actually flow test your preconnects research what psi your nozzles are rated for and what gallonage you want to put through them. You can then use the formulas to estimate what pressures you need. If done ahead of time you can memorize one or two pressures for your handlines you will need in a hurry.

    or remember

    Big Fire, Big Throttle. Little Fire, Little Throttle
     
  4. lomfs24

    lomfs24

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    Thanks for the help guys. I can appreciate the need to know your equipment in advance. There are a couple reasons why I asked for the formulas I did.
    1) for my own knowledge.
    2) I am fairly new to engine operations and am trying to come up to speed fairly quickly.
    3) Our FD has a wide range of problems. One building you might be on you can pull right up to it and use a preconnect handline. The next home you get to you end up humping 500' of 3" supply line to two 200' 1 1/2" attack lines. In that 500' you might raise between 100' to 200'. And every scenario in between.
    4) As our Chief is walking by you he will say "You have X amount of this size line feeding X amount of this size line raising X feet. What's your EP?" And within a reasonable amount of time you are expected to know the answer.
     
  5. DTD2

    DTD2 vote or die

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    After I took FEO I made the attached Engineers card and carried it
    in my helmet.


    [​IMG]


    The easy calculation is Discharge(engine) pressure= nozzle pressure + friction loss +/- elevation

    Get out and exercise your pumps and develop your own system is the best advice anyone can give you.

    Dennis
     
  6. roydamnmercer

    roydamnmercer

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    Throttle up until you lift 'em up and then set 'em back down.



    Seriously....I use a predetermined pressures for preconnects that give about 125gpm at the nozzle(we use Elkhart Sm-30's....120psi for 200', 110psi for 150', and 100psi for our 100')

    For "Two on a thief" lays...I give 'em 130psi until I get a chance to go back and figure and adjust accordingly.



    roy d...don't over think it