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Thread: GPM estimates

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    Default GPM estimates

    Just looking for some rough estimates for GPM in the following situations:

    1- 1 3/4" line, 200' long, w/ standard combi tip @ 125psi = ? gpm
    1- 2 1/2" line, 150' long, w/ 1" straight bore tip @ 70psi = ? gpm
    1- truck mounted deck gun w/ 3" plumbing and 1 1/4" straight tip @ 100psi = ? gpm


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    Forum Member FyredUp's Avatar
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    Quote Originally Posted by 3260e View Post
    Just looking for some rough estimates for GPM in the following situations:

    1- 1 3/4" line, 200' long, w/ standard combi tip @ 125psi = ? gpm What is the rated gpm of the nozzle?

    1- 2 1/2" line, 150' long, w/ 1" straight bore tip @ 70psi = ? gpm Depends if the nozzle pressure is 70 the flow is just under 250 gpm. Length of the line is irrelevant if the nozzle pressure is 70, the flow will always be the same. If however, you are saying the engine pressure is 70 the flow would be somewhere between 200 and 220 gpm (rough guestimate).

    1- truck mounted deck gun w/ 3" plumbing and 1 1/4" straight tip @ 100psi = ? gpm Again, 100 psi at the tip or 100 psi at the pump panel. If it is 100 psi at the tip the flow would be 460 gpm. I would guess the flow at around 400 gpm if 100 psi at the pump. Assuming roughly 20 psi friction loss in the piping and the gun.
    More specific info would make answers easier.
    Last edited by FyredUp; 01-12-2012 at 02:07 PM.
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    Forum Member CaptOldTimer's Avatar
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    Quote Originally Posted by 3260e View Post
    Just looking for some rough estimates for GPM in the following situations:

    1- 1 3/4" line, 200' long, w/ standard combi tip @ 125psi = ? gpm
    1- 2 1/2" line, 150' long, w/ 1" straight bore tip @ 70psi = ? gpm
    1- truck mounted deck gun w/ 3" plumbing and 1 1/4" straight tip @ 100psi = ? gpm


    You need to figure this out as you are the one taking the course and will get the grade.

    Use the information which was taught in class.

    BTW the handline nozzle pressure for a smooth bore should be 50 or 60 PSI.

    The deck pipe with a smooth bore should be 80 PSI.
    Last edited by CaptOldTimer; 01-11-2012 at 04:00 PM.
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    Are the PSI's nozzle pressure, PDP, or what?

    As far as your straight streams, that's what that 29.7 x D(squared) x √NP formula is for

    Fogs it's going to depend on what the setting is.

    Most of your hydraulics books will have the formulas you need.

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    3260e: Assuming that your psi numbers refer to engine pressure, then the following answers will be valid.
    1. With an automatic (TFT) nozzle or an Akron Turbojet set at 95 gpm your engine pressure of 125 psi supplying a 200 ft. preconnect of 1 3/4" hose will deliver 95 gpm. This is an inadequate flow to meet the NFPA suggested minimum flow of 150 gpm for structure fires. This line needs to be pumped at 165 psi with an automatic, a 150 gpm nozzle, or a 3/4" solid stream tip (88 psi nozzle pressure)
    2. The 150 ft. of 2 1/2" supplied at 70 psi of engine pressure with a 1" SS nozzle will deliver around 214 gpm with a friction loss of 17 psi and a nozzle pressure of 52 psi.
    3. Depending upon plumbing and elbows (2) and a straight run of 10 feet of 3" the prepiped nozzle with a 1 1/2" tip should deliver 600+ gpm at an engine pressure of 100 psi.

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    The combination nozzle is dependant of what pressure/flow it was designed for, and this varies greatly between all the brands and models.

    The 1" tip at 70 psi is 250 GPM, most people flow it at 50 psi producing 200 GPM. With a solid bore nozzle, if you want more GPM, then get a bigger tip and keep the nozzle pressure at 50, a 1⅛" tip @ 50 has less nozzle reaction force than a 1" @ 70. They flow the same GPM, but the bigger tips allows the water to move slower, lowering the reaction force.

    The formula for a solid bore tip is Diameter (squared) x 29.71 x square root of nozzle pressure
    GPM=D≤ x 29.71 x √NP

    The 1ľ @ 100 psi flows 464 GPM.

    Here's a link to Elkhart's technical section from their catalog. It's full of good information on general hydraulics.
    Last edited by txgp17; 01-27-2012 at 10:37 AM.
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