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Thread: CAFS Questions

  1. #1
    SBrooks
    Firehouse.com Guest

    Post CAFS Questions

    #1 Do any mfrs offer a 2000gpm+ water pump with a compressor? All I've seen advertised were around 1000gpm/200cfm or less.

    #2 Do automatic pressure governors work with cafs? Can't see why they wouldn't

    #3 If there is 'no friction loss' as I've seen some say, how do you gate between multiple differing lines?

    #4 How do you load concentrate?


  2. #2
    K A
    Firehouse.com Guest

    Post

    #1 Do any mfrs offer a 2000gpm+ water pump with a compressor?

    Yes all of them do


    #2 Do automatic pressure governors work with cafs? Can't see why they wouldn't

    Of course

    #3 If there is 'no friction loss' as I've seen some say, how do you gate between multiple differing lines?

    You don't, you get the same flow out of every line unless you low or increase the air and water flow to each line. If you use a 1 3/8" tip on each line say one 150 feet and one 400 feet you'll get the same flow

    #4 How do you load concentrate?

    Just like any other foam tank or foam system. We have our tank 1200 gallons located in the overhead to fill the A tank when needed with a garden hose and gravity


  3. #3
    Jim M.
    Firehouse.com Guest

    Question

    Who are the manufacturers with the most experience? While they all purchase the materials from the same suppliers who has the best track record in melding into an effective well designed apparatus.

    KA Assume you're flowing one 1 3/4 line and also a 2 1/2 line. Would your answer still hold or you would have to gate back on one of them? Do you actually carry 1200 galloms of foam or do I misunderstand your answer?

  4. #4
    SBrooks
    Firehouse.com Guest

    Post

    Why am I not suprised to hear from you KA?
    Truthfully, thanks for the info.

    So why would you use anything but the thinnest lines if the flow is determined solely by the nozzle?

    At the extreme, how would you use the deck gun and a hand line at the same time?

    Is the 1 3/8" size a good size for a smaller 1.5-1.75 handline? if so how would you take atvantage of a larger handline? In my head I had imagined a 150-200' 1 1/2" line with a 1" tip as a first in line and a 250' 1 3/4" with a 1 1/4" tip back up line. The 'Big gun' would be 500' 2" dead load with a 1 3/8" tip.

    Ideally, none of these lines would reach any further than a 50psi water only stream---figuring if they do, you should put on a bigger tip. Additionally, the nozzle reactions should be equivalent to 150 gpm @100psi np, 200gpm @100psi, and 330 @ 50 psi, respectively.

    What tip would you use on a master stream device?

    Has anyone published a "fire dept. hydraulics" book that covers cafs?
    Is anyone working on one?

  5. #5
    Mike C
    Firehouse.com Guest

    Post

    Who are the manufacturers with the most experience?


    Pneumax and Darley and Oden


    While they all purchase the materials from the same suppliers


    Not really


    who has the best track record in melding into an effective well designed apparatus.


    Same three above


    Assume you're flowing one 1 3/4 line and also a 2 1/2 line. Would your answer still hold or you would have to gate back on one of them?


    Depends how you set the rig up, a set of solinoids hooked to the air valves and water valves means you just pump same pressure no matter what you are supplying or how many. For whatever it is worth you always gate back a CAFS line. A valve isn't opened all the way because you are only flowing 20 to 200 gpm ever.


    So why would you use anything but the thinnest lines if the flow is determined solely by the nozzle?


    Flow and hose size determine flow with cafs. Only so much air and water will fit expand in a line 60 to 90 gpm with 1 3/4" and 100 to 200 with a 2 1/2"


    At the extreme, how would you use the deck gun and a hand line at the same time?


    Open each line to the mark for that size line ie 1/8 open or so and turn the air on to the preset setting


    Is the 1 3/8" size a good size for a smaller 1.5-1.75 handline?


    It is the ideal and the most used.


    The 'Big gun' would be 500' 2" dead load with a 1 3/8" tip.


    2" wouldn't offer much improvement over 1 3/4" A 2 1/2" with a 2" or 2 1/2" tip or gun with the same tip would be the big gun


    Ideally, none of these lines would reach any further than a 50psi water only stream---


    Well, you're off by at least 50 feet on the reach idea. CAFS goes much further


    figuring if they do, you should put on a bigger tip. Additionally, the nozzle reactions should be equivalent to 150 gpm @100psi np, 200gpm @100psi, and 330 @ 50 psi, respectively.


    Not really. Reach is a function of air flow not tip size. Hose ha to grow to gain reach. Nozzle reaction is lower but momentary reaction is higher.


    What tip would you use on a master stream device?


    2" or 2 1/* or 2 1/4 or a TFT master with the guts out. A tele squirt with a 2 inch smooth bore at 200 gpm looks just like a 1200 gpm water stream


    Has anyone published a "fire dept. hydraulics" book that covers cafs?
    Is anyone working on one?


    Why? Friction loss with water flowing 1000 gpm is listed as 210 psi with 2 1/" hose 100 feet long. In fact the loss is 6 to 8 psi. The balance is turbulance loss. There isn't any turbulance loss in a CAFS stream up to 400 feet. So loss at 60 to 90 gpm or 100 to 200 gpm is insignificant

    High flows with cafs are limited to the size of the ccmpressor. Pretty much limited to 200 to 240 cubic feet of air and 200 to 240 gpm of water. Smaller tip wetter foam larger tip dryer foam. One other thought this stuff isn't new, if has been in use in hundreds of rigs since the mid 80's.

  6. #6
    e33
    Firehouse.com Guest

    Post

    can't delete it..so heres this wasted space

    [This message has been edited by e33 (edited October 30, 1999).]

  7. #7
    Firehose
    Firehouse.com Guest

    Post

    Sbrooks

    We have a Waterous Eclipse on order. it is a 1500 GPM pump with 200cfm compressor and a fire research pressure governor. Ill let you know how it all works later.
    Good Luck

  8. #8
    SBrooks
    Firehouse.com Guest

    Question

    'nuther question....

    You mentioned a set of solenoids on the air and water valves:
    I assume these have a preset setting for preconnected lines and that with the little friction loss with cafs, non preconnected lines probably get a preset as well.
    Would this be like taking a water only pump, presetting the governor to say 200psi, and "presetting" the valves for discharges--ie putting limits on how much the valve can open, in effect gating back from 200 to the desired engine pressure?

    Do you need a separate pair of air/water solenoid valves for each attack line, or could you take a discharge and put a wye on it and flow two different length / size lines from it, perhaps gating one back, as you do with water?

    Is it possible to manually control the setting of the lines...i.e. one discharge that could pump, depending on what is hooked to it, anything from 100' of 1" to 400' of 2.5"? How would you determine the correct settings?

    If we currently use the following lines, what would be an appropriate equivalent, using CAFS? (Smoothbores OK)
    100' 1 1/2" 100psi Automatic 95 gpm
    200' 1 3/4" 100psi Automatic 180 gpm
    350' 2" 100psi Automatic 180 gpm
    250' 2 1/2" 1 1/8"//1 1/4" tips @ 50psi

  9. #9
    Mike C
    Firehouse.com Guest

    Post

    Scott,

    Sounds like you understnad gating caf lines.

    You could use seperate solinoids, or none. We use two, one for five short lines and deck guns. Another for 400 foot lines.

    You can use a gated wye if you know what you are doing. Most folks will have problems with it.

    Presetting valves doesn't have anything to do with length of line. I has to do with wet or dryness of the foam.

    If we currently use the following lines, what would be an appropriate equivalent, using CAFS? (Smoothbores OK)
    100' 1 1/2" 100psi Automatic 95 gpm

    a 1" Caf line

    200' 1 3/4" 100psi Automatic 180 gpm

    A 1 1/2" caf line

    350' 2" 100psi Automatic 180 gpm

    A 1 1/2" caf line

    250' 2 1/2" 1 1/8"//1 1/4" tips @ 50psi

    A 1 3/4" caf line

    Sounds like you have too many chices for flow and diameter

  10. #10
    Rockies
    Firehouse.com Guest

    Post

    we just push a button and all lines make cafs. No valves to play with no matter what the length of the lines.

  11. #11
    Dalmation90
    Firehouse.com Guest

    Post

    Why? Friction loss with water flowing 1000 gpm is listed as 210 psi with 2 1/" hose 100 feet
    long. In fact the loss is 6 to 8 psi. The balance is turbulance loss. There isn't any turbulance
    loss in a CAFS stream up to 400 feet


    Just to correct a term, Friction loss is not seperate from turbulence, IT IS turbulence , to wit a generally accepted definition of Friction Loss:
    Friction Losses
    The head, pressure, or energy (they are the same)lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, and restrictions caused by fittings. Water flowing in a pipe loses pressure or energy
    as a result of friction losses. (Water Quality Association, Lisle, IL)

    Air is compressible, and energy is stored in that compressed air until it released at the nozzle. I suspect the air is also affected by turbulence, but the additional energy stored in it helps to overcome the losses to turbulence, thus the longer hose lines.

    As an aside, the ability of compression to store energy is why a charged hose line with 100psi of air is much more dangerous than a line with 100psi of water. Be aware of this when using fire hoses and adapters with air for training purposes or water rescue. Yep, the hose should hold the same pressure whether gas or liguid, but the gas will have a lot more energy stored in it, and will be much more destructive if there is a failure!

    Matt

  12. #12
    K A
    Firehouse.com Guest

    Post

    . In fact the loss is 6 to 8 psi. The balance is turbulance loss. There isn't any turbulance
    loss in a CAFS stream up to 400 feet

    CAFS allows the same effect as Rapid water. It simply made the water follow itself better versus bounce around. Union Carbides (FC Mag Jan 1969) testing in NY, SF akron and else where proved 6 to 8 psi fl at 1000 gpm the difference they stopped the turbulance.

  13. #13
    Dalmation90
    Firehouse.com Guest

    Cool

    CAFS allows the same effect as Rapid water.
    the difference they stopped the turbulance

    Well, hate to write a long letter, but it's important that people understand the physics involved here instead of perpetuating myths.

    If the above was true, you would expect to see dramatic reduction in friciton loss when running a straight Class A foam system as it is a chemical property in the Polyethelyne ???? in slick water that orients all the water molecules in the same direction to reduce turbulance. I'd think adding compressed air tends to actually increase the turbulence -- and this isn't neccessarily bad. Without turbulence to keep the ingredients mixed, the air would want to seperate from the water/foam mixture -- think of white water rapids -- the rough surface of rocks under the river increase the turbulence and traps air. Once the stream either a) has it's bed smooth out or b) widens so the water is moving slower, the turbulence decrease, and the air leaves the water, and thus no more white water.

    The turbulence is still there, and Friction Loss is a function purely of turbulence. You can't eliminate it, but you can reduce the causes of turbulence by things like smoother hose liners, lower velocities, bigger hose, chemical additives.

    The addition of Compressed Air adds energy to the system, and that extra energy can be used to overcome losses of energy to turbulence.

    Hopefully this example will make some sense.
    Imagine taking a ruler, and putting a finger from either hand on it on opposite ends and pushing. You will feel "One Finger" of force on the other hand as you push. The ruler is incompressible, so the force is transferred directly. You see this on fire streams when you take a "static" pressure -- when you're not flowing water, the pressure is the same throughout the system.

    Now water is a liguid, and it's very susceptible to turbulance when it begins to move through a hose. The loss in energy from the static pressure to the flowing pressure is your Friction Loss, i.e. loss to turbulance.

    Now take a spring that's 12" long and squeeze it down to 1" between the fingers you just had the ruler between. Because a spring is compressible, it shrinks in size unlike a ruler would. You will feel "One Finger" of force between the two fingers on the compressed spring. Now imagine taking 12 springs, compressing each to 1" long, and putting them all end to end and pushing...at the end of the 12 springs, you still only feel 1 finger of force. But let go of all twelve of them, and you release "12 Springs" of energy. Because you could compress the springs, you could store energy in the same space where an incompressible thing like a ruler or some water couldn't.

    For most firefighters, all this doesn't matter except to say that CAFS will go considerably farther through a hose than plain water. But let's not give explanations or definitions that a patently incorrect. If someone can see a problem in my physics, let me know, but I think it makes a lot more sense than saying that adding air reduces turbulence by aligning the water molecules!

    Air is just like springs. By compressing it, you are storing energy. And this energy is used to overcome losses to turbulence, resulting in a lower observed friction loss. Remember, we PUMP water but COMPRESS air, and there's a reason we use different terms for those two activities!

    Matt

  14. #14
    K A
    Firehouse.com Guest

    Post

    You must be right. With a cap gauge on a 50 and a 400 foot line the pressure reads 110 psi ststic. With both lines flowing at 110 psi inlet the gauges read 110 psi. Loss would be "dick".

  15. #15
    SBrooks
    Firehouse.com Guest

    Post

    Friction loss would explain why the momentary nozzle reaction is higher than the steady state nozzle reaction.

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