1. #1
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    Default More CAFS Questions

    To begin, I am only a few months out of the academy for a large north Texas fire department. We are purchasing all cafs engines every time we replace part of our fleet and are at the point that over a third of our engines are cafs. We use Rosenbauer Spartans with the rear mount pumps and foam pro foam systems.

    Now to the cafs portion. A family member of mine who is a firefighter at another department and I were talking about our engines and cafs as I was required to become a certified driver/operator at the end of my academy. during that conversation he asked how my department uses cafs for attacks and I went through the explanation that it is deployed the same as a normal water based attack but the method of extinguishment is a little different as we are taught to "paint" all surfaces of the room instead of the typical direct indirect, and combination attacks.

    He asked what gpm we flow our lines at using cafs and I was dumbfounded as I thought it didn't matter. My reasoning is that we flow our cafs lines between 90 and 120 psi for a typical 1-3/4" handline using a 15/16 smoothbore nozzle, and the air compressor for the cafs is tuned to match the pressure (this is the purpose of putting the selector to auto as I was taught in pump opps) Now my family member mentioned that to get the proper finished cafs you must flow between 75 - 90 gpm of water for a proper 1:1 ratio of air and water/foam solution.

    so my question is, does water flow matter if your air compressor is matching the psi of the fire pump?


    i'm not sure if I am clear as mud on this subject or my question but maybe this is a good base to begin from.
    Last edited by trevolp; 02-27-2008 at 01:26 AM.

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    Hi trevolp,

    "so my question is, does water flow matter if your air compressor is matching the psi of the fire pump?"

    YES it matters. They are two distinct differences here. PSI and GPM. For any CAFSystem to work air psi and water psi must be equal (or within 10 psi). Proper gpm flow is needed to meet or exceed the critical application rate. This is true regardless if you are flowing water, solution or CAFS.

    What you are looking for in your CAFS operation is a ratio of about 2:1 for your fire attack flow. That is 2 gpm of solution to every 1 cfm of air. I know that your truck will deliver approximately 100 gpms of solution and 50 cfms of air (2:1) when flowing at 100 psi main pump pressure thru a 1 3/4" line with a 15/16" tip on the nozzle. Your family member talks about 1:1 which is used by some departments, but the norm seems to be 2:1. 1:1 will give you less gpms and more cfms.

    Your method of extinguishment is correct by "painting" the surfaces.

    Hope this helps.

    Be safe,

    Capt Lou
    "GotFoam?"
    Last edited by CaptLou; 02-27-2008 at 10:50 PM.

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    So what gpm's do i need to flow and how do i ensure this? ie....should i gate back the line? or will the system when on auto give me the proper ratio.

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    Quote Originally Posted by trevolp View Post
    So what gpm's do i need to flow and how do i ensure this? ie....should i gate back the line? or will the system when on auto give me the proper ratio.
    trevolp,

    Your gpm flow requirement is dictated by the size of the fire you are fighting. You can get only so much liquid out of a given size line. The old saying, "Big Fire, Big Water or Small Fire, Small water" is still applicable in a CAFS attack. So if more gpm is required to extinguish a fire, you need to pull a second line equal and/or larger or start with a larger line. Like I said in my previous post you will be flowing about 100 gpm with your 1 3/4" line using a 15/16" tip.

    When the Auto/Sync control is in the "AUTO" position, all that it does is keep water psi and air psi equal. Which is necessary for CAFS to work.

    The water discharge valve for the respective CAFS discharge adjusts your “volume” ratio. The more you open the water valve, the more solution is put into the line and less air will be allowed into the line. The liquid is the dominant mass. Even though the air switch is on and wide open, the more liquid you add automatically pushes back or holds back the air. Hence when you start to close off the water valve more air will be allowed into the hose and the ratio starts to go the other way. For your truck, 2:1 happens when the water discharge valve is about 3/4 to all the way open and the air switch on. Again, we are talking about "VOLUME" not "PSI".

    So if you "gate back the line" to much, what you are doing is starting to flow less GPM of water and more CFM of air. This will give you a "dryer" foam which is what you DO NOTwant for an interior fire attack. You need to flow gpm to put the fire out.

    Hope this helps.

    Be safe,

    Capt Lou
    "Got Foam?"

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    Thanks Capt,

    That was extremely helpfull and was the exact info I was searching for.

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    Default CAFS here's a little more.

    There is a misconception going around that CAFS requires the same water flow or volume as a plain water application. This is not right. Every legitimate test and evaluation of CAFS has proven that the foam is many more times effective that the water application it has been compared too.

    And I can not understand why some CAFS manufacturers are promoting the use of high water volumes for the CAFS and then recommending small 15/16 tips on the hose. You’d be better off using the non-kinking 1 inch booster hose and a full flow 1 inch ball valve for a nozzle, which is exactly what we used to use on the wildland CAFS or WEPS units that we used in the forest service to extinguish full blown house fires in the early years of the CAFS development.

    Just keep in mind that a foam solution with a half of one percent concentrate will generate a full range of foam expansion from 1 part water to about 60 parts air, or a 60 to 1 expansion range. And please remember the foam IS compressed so a lot of foam will fit into a small hose. I consider a 1-3/4 is a large hose when flowing CAFS. I disagree with reducing the discharge down to a 15/16 when you can better flow the full 1-3/4 without the tip? Of course you will need to reduce the amount of water in the hose in order to get the true CAFS compression and high volume FOAM flow in a controllable discharge.

    I prefer a 20 parts air to 1 part water (3:1) for interior fires because the foam covers more area faster and with less water. Consider, If you scoop up a handful of the dense fully expanded foam you will be holding a product that is more than 99 percent water. It’s in a whole different form than when it is more liquid and normally runs down the wall and out the door as contaminated waste. The thin films of the bubbles absorb heat much faster than water droplets and convert to positive pressure steam to extinguish fires ahead of the foam blizzard.

    I hope this helps and not just add to the confusion. I’ve been using all kinds of CAFS for nearly 30 years and this has always worked for me.
    Mark Cummins

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