1. #1
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    Default Pumping to a gated wye.

    You are at a fire in an elementry school. Your preconnected lines will not reach so the captain decides to extend your hose pack with 2-1/2" line supplying it. You guessed it .. the pump operator does not know how much hose is on the ground. Oh yea. The appliance used for the wye connection is a 3-way. You know for a fact that one hose pack was connected however there is a chance that 2 more were put into service. With all the excitement you are just not sure. How will you determine your engine pressure? One more thing, there is too much radio traffic for you to check .

  2. #2
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    First of all this is the 21st century, so we wouldn't be supplying a wye without a pre-set relief valve would we? Certainly not, if we have any understanding of hydraulics, right? No professional engineer would suggest such a thing and if faced with the prospect would document the dangers and present them to his supervisor and present safer alternatives, wouldn't he?

    Say this 2 1/2" line you can't see the end of (see below for how you always know for sure) requires 140 psi at the end to supply your 100 foot 1 3/4" hose pack at 200 gpm.

    Certainly the relief valve on the wye was set at 140 psi back at the station after field testing. If not shame on you!

    Using a wye without a relief puts the crew at big time risk. The 200 gpm flow through say 500 feet of 2 1/2" hose requires a pump discharge pressure of 190 psi. Two lines would require 320 and three you did say three way 500 psi. Don't let the high numbers scare you and flow would result in the same percentage increases of 68% and 56%, right?

    Now, here is where life gets fun and why you'd never really use a wye without a relief valve. If only two lines are in use and one line shuts down the other line will experience at least a 56% increase in pump pressure. Or 180% ncrease in momentary nozzle reaction if the line is not shut down very slowly. With a pressure relief dump valve both surges would hit the ground. Using a wye without the dump makes sure your governor and pressure relief valve have no ability to protect the crew. That not a good thing, right. All the above is also true with a highrise setup as well.

    If you've really thought about this you'd never do it would you? Try the math with three lines with two shutting down at the same time. You are almost always pusing the burst limit of the hose.

    If the goal is to hurt the firefighters on the lines then use the wye without the dump. A dump can be addede to any wye with an add on device for a couple hundred bucks.

    Try this with a smooth bore, you'll have the greatest danger of getting someone hurt, fixed flow fogs and rotary flows would be next and automatics dead last in sevarity of the increase in reaction and chance of losing control of the line.

    If you wouldn't operate a line without a relief valve or governor why would you set up your apparatus and crews to operate without one?????

    Now lets talk about three way wyes supplied by 2 1/2" hose at lengths you can't see the end of. Say 500 feet. If the average 1 3/4" line needs 150 to 180 gpm when run as a preconnect it is safe to assume that would be the goal flow from a wyed line wouldn't it? SO that means you need to start out with no less than 225 to 318 psi for friction loss in the 2 1/2", a nozzle pressure of 50, 75 or 100 psi, plus the loss in the line 30ish pounds per 100 feet. SO simply throttle up to 448 psi and you're right on.

    No that is not what will happen. The averge engineer will make a wild *** guess and pump 150 or maybe 200 psi and you'll be flowing 47 to 70 gpm out of each line, right? SOme aspects of firefighting can get you killed doing stupid stuff like this. Or simply allow property to burn down around you. Supply a wye with a 2 1/2" line beyond your ability to see the end of the line???? Yeah right!

    Knowing how much hose is left in the bed>>>>It all gets down to loading your hose on the pumper correctly. Every 100 feet you should flip the hose so the stripe or label is down, a quick look at the bed and you can count the hundreds of feet of hose in the bed. From the ground you will see stripes or labels every other length of hose. SO 8 left and you started with a 1000 foot bed the lay is 200 feet.

    If you load your hose couplings forward or coupling out you can simple count the couplings remaining in the bed. Obviously couplings out is easier to count and to advance.

    Or some departments mark the hose bed with marks to indicated the amount of hose missing ie 100, 200, 300 etc.

    In any case laying hose is not an emergency, if done right no one gets hurt when it is pulled and progressive departments think these items out before the fire, after all we've being using hose beds for 100 years, it is not a new issue. These items should not be left to chance.

    It is safe to say there has been a bigtime erosion in engineer skills.

  3. #3
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    Play, Do you know LHS?

  4. #4
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    Consider a 400' stretch of 2 1/2", a wye, and two 200' stretches of 1 3/4".

    In the first set up, the nozzles are 7/8" SB
    PDP(1 line): 140
    FL(400' 2.5" @ 160 gpm): 21
    FL(Device): 5
    FL(200' 1.75" @ 160 gpm): 64
    NP(7/8"): 50
    NR(7/8" @ 50 psi): 57 lbs

    PDP(2 line): 200
    FL(400' 2.5" @ 320 gpm): 82
    FL(Device): 5
    FL(200' 1.75" @ 160 gpm): 64
    NP(7/8"): 50
    NR(7/8" @ 50 psi): 57 lbs

    PDP(2 lines, 1 shut down): 200
    FL(400' 2.5" @ 192 gpm): 30
    FL(Device): 5
    FL(200' 1.75" @ 192 gpm): 92
    NP(7/8"): 72
    NR(7/8" @ 72 psi): 82 lbs

    Second Scenario, 100 psi pressure regulating nozzles

    PDP(1 line): 180
    FL(400' 2.5" @ 150 gpm): 18
    FL(Device): 5
    FL(200' 1.75" @ 150 gpm): 56
    NP(automatic): 100
    NR(150 gpm @ 100 psi): 76 lbs

    PDP(2 line): 235
    FL(400' 2.5" @ 300 gpm): 72
    FL(Device): 5
    FL(200' 1.75" @ 150 gpm): 56
    NP(automatic): 100
    NR(150 gpm @ 100 psi): 76 lbs

    PDP(2 lines, 1 shut down): 235
    FL(400' 2.5" @ 198 gpm): 31
    FL(Device): 5
    FL(200' 1.75" @ 198 gpm): 98
    NP(automatic): 100
    NR(198 gpm @ 100): 100 lbs


    So...the smoothbores' nozzle reaction increases by a greater percentage than the fog nozzles, but the fog nozzle jumps up to a much higher number...either the guys can hold 82 lbs or they can't.

    This phenomenon is worsened the greater the friction loss in the large line is compared to the attack lines...e.g. the longer or smaller. Or for best results, use your largest supply line with your smallest attack lines.

    The smaller attack lines act as a pressure regulating device on their own accord, especially if you already start at high FL/section in the attack lines, but manageable flows & nozzle reactions.

    I personally think that each company should pull it's own line, eliminating any of these wye problems.

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