Thread: CAFS and GPM

  1. #1
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    Default CAFS and GPM

    I already know that a 15/16 smooth bore is an optimal type of nozzle for CAFS. Fog nozzles will break up the foam bubbles too much. I'm just wondering about the GPM flow and if there is any loss of GPM when choosing to flow CAFS instead of just water. I've never used a pitot tube to test flow out of smooth bores, but I'm guessing that we are flowing about 150gpm out of a 200 ft 1.75" hoseline with a smooth bore when engine pressure is at 120psi.

    My other "best guess" is that flow is diminished slightly when flowing CAFS so instead of 150gpms, we are flowing CAFS plus about 135gpms.

    OR I AM CRAZY.

    Please prove me wrong so I can learn something!!!

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    Hi firegeek8096,

    You are correct in the fact that when flowing CAFS your gpm flow in less than plain water flowing thru the same size line and nozzle tip.

    The reason for this is that the internal size of a hose can only be filled with so much "mass". Regardless if that "mass" is liquid only or liquid and air. So the air takes up some of the space and the liquid takes up some space.

    My experience is that an 1 3/4" line with a 15/16" tip will flow around 90-100gpm of liquid with around 45-50 cfm of air, (2:1 ratio). This, at 100 psi main pump discharge pressure.

    I would like to ask you why are you pumping at 120psi main pump discharge for your 1 3/4" CAFS handline, or any handline for that matter? It can be done, but the nozzle reaction is much higher at 120psi compare to 100psi and the nozzleman has to "fight" to hold the nozzle. I state this from experience. I would suggest trying to pump at 100psi and see if your nozzle people are more comfortable and have better control of the nozzle.

    Hope this helps.

    Be safe,

    Captain Lou
    "Got Foam?"

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    we set the PDP at 120psi for our 1.75" CAFS line because we can handle it and it puts more gpm on the fire than at 100psi PDP.

    Our neighboring district (strictly volunteer with minimal staffing) suggested we pump our CAF's lines at 80psi if we only have two on the engine. I worry about the minimal gpm's we would get from this kind of pressure. If attacking with one from the outside, there are plenty of techniques to use to control the handline with one.

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    Quote Originally Posted by CaptLou View Post
    Hi firegeek8096,

    You are correct in the fact that when flowing CAFS your gpm flow in less than plain water flowing thru the same size line and nozzle tip.

    The reason for this is that the internal size of a hose can only be filled with so much "mass". Regardless if that "mass" is liquid only or liquid and air. So the air takes up some of the space and the liquid takes up some space.

    My experience is that an 1 3/4" line with a 15/16" tip will flow around 90-100gpm of liquid with around 45-50 cfm of air, (2:1 ratio). This, at 100 psi main pump discharge pressure.

    I would like to ask you why are you pumping at 120psi main pump discharge for your 1 3/4" CAFS handline, or any handline for that matter? It can be done, but the nozzle reaction is much higher at 120psi compare to 100psi and the nozzleman has to "fight" to hold the nozzle. I state this from experience. I would suggest trying to pump at 100psi and see if your nozzle people are more comfortable and have better control of the nozzle.

    Hope this helps.

    Be safe,

    Captain Lou
    "Got Foam?"
    Our PDP is preset at 120psi because we based it off of our 1.75" preconnects. they are 200ft long, which gives the line a total of 70psi FL. Add the 50psi NP and you get 120psi. We don't want to compromise our gpm flow by pumping our handlines at lower pressures, such as 100psi PDP. Todays fires put out a lot of btu's plus higher Heat release rates due to all the plastics used in so many products, so we feel the need to fight the fires with more water, plain and simple.

    I really enjoy this article somebody else mentioned here in another thread that has to do with the gpm flow of handlines.

    http://firenuggets.com/x_ardsilliill.../comella27.htm

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    The FL calculations for CAF solution are different than those for water. Your CAF needsto be balanced GPM/CFM. We use a 2 gpm/1cfm for wet foam and a 1gpm/2cfm for dry. So at 100 psi PDP at 150 GPM we have 75 CFM of air flowing. This is with 200' line with 1" tips. This is a very easy line to control and does a great job of extinguishing fire.

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    Hi firegeek8096,

    Thank you for your information and explanation. I understand your response but you appear to be thinking as if you are still in a "water" world, however you are in a "CAFS" world and you must adjust your tactics and thoughts or someone may get hurt.

    As Asst48 stated, "The FL calculations for CAF solution are different than those for water." In fact friction loss in a CAFS handline is really only measurable until you get into the 2000 plus feet of 1 3/4" hose lines. What you need to understand is that CAFS is a "pneumatic operation" not a "hydraulic operation".

    Also the use of Class A foam and the application of it via CAFS is a powerful combination that makes the water so much more efficient in the extinguishment process compared to plain water.

    I would like to suggest that you take a Class A foam class that can explain how it (class A foam) works for "us" in the extinguishing process and couple it with a CAFS tactics class to better use a CAFSystem.

    Operating a CAFS handline with main pump discharge pressure of between 80-100 seems to be the norm in the CAFS world. The only time I go higher is for long hose lines of 2000 feet or greater or for CAFS master streams. This regardless if you are a career firefighter or a volunteer firefighter.

    Hope this helps,

    Captain Lou
    "Got Foam?"

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    CaptLou,

    thanks for providing your expertise on this topic. I AM learning a lot here, so I appreciate it very much. However, I still have questions.

    If the FL in a CAF handline is negligible, then I should drop my PDP to 50 psi if I want 50psi at the tip? Leaving friction loss out of the pump discharge pressure equation is foreign to me (I am still thinking in a water world).

    If the FL in A CAF handline is negligible, then what factors do I need to take into consideration that would make 100psi PDP the optimal pressure for a 1.75" CAF handline?

    I'll be keeping my eye out for CAF systems training in the area.

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    1 3/4 handline with smoothbore flowing CAFS should have a NP of 100 PSI'ish. So with little to no FL the PDP shopuld be 100 PSI'ish.
    IACOJ - Senior Jake

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    Default Cafs

    Like Capt Lou said.... pdp should be no more than 100 psi unless u have master stream cafs or lines over 2000 foot. Set it to 100 psi and forget it.
    open discharge valve about a fist legnth for dry cafs and open all the way for wet cafs.
    I still want to have Lou come up and teach my company though.

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    Quote Originally Posted by Engine305 View Post
    open discharge valve about a fist legnth for dry cafs and open all the way for wet cafs.
    That not neccesarily true. For your system I'm sure it is. For our Hale system we open discharge valves all the way. To control the wet/dry of the foam we simple hit the up or down arrows on the control head.
    IACOJ - Senior Jake

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    One of the big factors of what you are flowing will be you type of hose. We had started with one brand and due to some kinking problems at the lower pressures we Switched Brands of Attack Line and not only eliminated the Kinking but got a 15 gpm increase in output.
    The biggest Thing you need to do is get the hands on training by a good instructor. Did you pump manufacture offer training either free with the system or for a fee?. Every system is a little different. Even the same system on a different truck can be adjusted so its output is different. After your operators master the system the line firefighters must train under realistic condition to see what pressure they can work with and to see the knockdown ability of there lines.
    As for Nozzles we start with an 11/8" for less restriction and most fires that gets taken off and put in the nozzlemans pocket and we use the 13/8" waterway in the open bail.

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    Quote Originally Posted by captaincvfd View Post
    One of the big factors of what you are flowing will be you type of hose. We had started with one brand and due to some kinking problems at the lower pressures we Switched Brands of Attack Line and not only eliminated the Kinking but got a 15 gpm increase in output.
    captaincvfd,

    What type/brand of hose did you switch to? Our CAFS pumper is due here in less than a month and I have been digging for ideas on what to do for the 1 3/4 lines and haven't seen much about hose that is somewhat kink resistant. What hose were you using before? Any info would be much appreciated!

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    We're very new to CAFS but when get a kink in the 1-3/4" I don't notice any particular impact on the stream. Have not monitored the flow meter kink vs unkinked though. Operating at 100psi .3% Chemguard w/new ATI hose

    What problem are you getting when hose is kinked?

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    We have gone to Ponn Supreme it is rubber lined and has a little larger bowl size, and the outer jacket is coarse enough to hang on to with soapy gloves.
    We found that one or two kinks had a minor effect but if you started navigating to many corners at the lower pressures we were degrading the bubbles and the actual flow rate on the meter as well as affecting the working stream. The Supreme was a big improvement BUT we still Chase out the kinks just like any hose.
    The Ponn is a little more expensive and has a longer lead time but it is also made in the USA, and it holds up well to the abuse and is certified for use with CAF's.
    I am sure there are other brands that work as well but we have had good luck with the Supreme.

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