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  1. #21
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    For the everyday job, as in the story I told earlier about a long past chief, you really wouldn't see a significant difference. It's those once every couple of years jobs where you max out your engine and need every bit of water flow capability that you can muster that it really shows up. And granted, the difference won't be as dramatic with 4" as it would be with 5".

    The offer to lend you our setup still stands. I could even be talked into bringing it over. I've been needing a good excuse to come and look at your engine.


  2. #22
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    Quote Originally Posted by chiefengineer11 View Post
    For the everyday job, as in the story I told earlier about a long past chief, you really wouldn't see a significant difference. It's those once every couple of years jobs where you max out your engine and need every bit of water flow capability that you can muster that it really shows up. And granted, the difference won't be as dramatic with 4" as it would be with 5".

    The offer to lend you our setup still stands. I could even be talked into bringing it over. I've been needing a good excuse to come and look at your engine.
    Sam, thank you and I certainly hear where you are coming from. We have several LDH siamese and triamese devices (manufacturered types). The device you speak of sounds pretty similar. I always appreciate your input.

  3. #23
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    MG3610:
    The equation you are seeking is the Hazen-Williams formula that relates velocity of the fluid, the roughness and size of the conduit to the pressure loss per unit length. There are many forms of this equation, all adjusted to make it easier for the person calculating the loss to handle the numbers. The constant “c” is adjusted for the units of measure used in the inputs. When doing hydraulic problems on the fireground, I try to keep it as simple as possible. I usually start with 3” hose with 2 ½” couplings. This is the easiest problem to calculate since the Fl is simply the gallons per minute / 100 and that value squared. Suppose we wanted to move 500 gpm through 100’ of 3” line (engine to engine) Take the 500 and divide by 100 or 5 and then square the 5 = 25 psi. friction loss in 100’ of 3” hose with 2 ½” couplings. Suppose you wanted to practice running a 100’ relay with 4” hose. What loss could you expect to have between the engines at 500 gpm? The formula says c * Q^2 * L / d ^ 5 = Fl. Since the length is the same and the flow is the same, we can toss them out and compare only the diameters, but the formula says to use d to the 5th power. Well 3 to the 5th is 3 * 3 * 3 * 3 * 3 = 243 and 4 to the 5th is 1024 also the diameter is in the bottom of the equation (inverse relationship) the loss in the line will go down by the ratio of 243 / 1024 or 0.237 times the loss in 3” line which is Q ^ 2… so the loss at 500 gpm goes from 25 psi down to 5.925 psi. Notice that the loss is about Ό of the loss for 3”… so modify the 3” equation to Ό Q ^ 2 for 4" line. Want to understand why some hose has less friction than another even though they are the same size. Try comparing 5 to the 5th with 5 Ό to the 5th.
    You are on a 3 man engine company, and you want to practice running an 800 ft relay of 4” line. Picking this up after the exercise is a pain. Replace the 800 ft of 4” with 200 ft of 3” from the storage rack. Doing the math for 1,000 gpm through 800” of 4” is Ό * 10 * 10 * 8 = 200 psi friction loss. Compare this to 200 ft of 3” W/ 2 ½” couplings. 1 * 10 * 10 * 2 = 200 psi friction loss. You can now practice relays but still be available to respond simply by breaking the spare 3” off the engine and responding. Play the numbers game for 2 ½” hose and get even shorter practice lays. 50’ of 3” matches 750’ of 5” for loss. Contrary to some posters on here, there is no upper limit for flow through a conduit. You will need to stop when you exceed the operating pressure for the hose, you exceed appliance test pressures, relief valves open, the pump runs out of engine rpm or out of horsepower. The physics continue onward until something else fails.
    By the way, the loss inside the pump panel will include the losses inside the discharge manifold of the pump as well as any change in direction (elbows) in the casting. A Watrous 2 stage has a 180 degree bend between the main suction manifold and the intermediate suction before the second stage intake. You must look at the travel of the water from the volute around the pump impeller right on through the discharge manifold and out to the connections at the outside of the pump panel. Just looking at the piping beginning with the valves doesn’t tell the whole story.

    Kuh

  4. #24
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    The NFPA flow rating system is based on ideal flow through a given hose size, which is expressed in a water velocity of 16.33 ft/sec in the hose. The rating system uses the first permanent fire hose connection on each outlet to be counted as the size of the outlet. Rating is NOT based on piping or valve size inside the truck.

    You'd be surprised how much water you can fit through a short piece of 2½" piping. But don't ever expect to get close to what a true 3" or 4" discharge can handle. You won't have to try too hard to get 1,000 GPM out of a short 2½" port that is plumbed directly to the discharge manifold.

    For example, Hale rates their 3" discharges (directly off the discharge manifold) at 1,500 GPM, even though the NFPA credits them with 375, a difference of a factor of 4.

    I'd bet the farm that your two 3" lines to one 4" would outflow a single 2½" to 4" setup, but I'd do a real world flow test of the single 2½" to 4" setup first. If the single port flows what you need, than I'd just stick with it.
    Last edited by txgp17; 08-23-2009 at 07:19 PM.
    The American people will never knowingly adopt Socialism. But under the name of 'liberalism' they will adopt every fragment of the Socialist program, until one day America will be a Socialist nation, without knowing how it happened. --Norman Mattoon Thomas, 6 time presidential candidate for the Socialist Party of America

  5. #25
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    CE11,

    Can you send me your email address. I found a photo that youll appreciate.

    mg0178@yahoo.com

    Thanks,
    Mike

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