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Water Hydraulics

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  • Water Hydraulics

    Is there a way to calculate actual flows of a hose if I know the pump pressure, hose lengths, nozzle size tip size for smooth bore and nozzle ratings for a fog?

    For example, I have a calculator on my phone that says in order to pump an 1.75" line that's 200' long with a fog/automatic nozzle that is rated for 135 GPM @100 PSI I need a pump pressure of 156 PSI.......... What is that nozzle flowing if the truck is being pumped at 130 PSI.......

    Or if a 300' long 2" line with a 15/16" smooth bore nozzle with a nozzle pressure of 60 PSI will flow 202 GPM with a needed truck pressure of 158 PSI. How do I calculate nozzle pressure and GPM if that same line is being pumped at 130 PSI?

    Both Scenarios are with zero elevation change for simplicity reasons.......

    Any and all incite will be very much appreciated.

  • #2
    This probably isn't the answer you are looking for, but....

    Until you know actual friction loss for your hose, all you have is theoretical numbers that can be way off of actual. The best way to determine actual flows is to get out and determine it with your entire package- pump, hose, nozzle. For the smoothbore, you need a pitot gauge to measure tip pressure. It's more difficult for the fog, you need an in-line pressure gauge for that. There is a huge amount of variability in FL in the hose on the market today, to assign one number to all is not only foolish but dangerous.

    One other way to test what you are actually flowing is to utilize a flow meter. There are stand-alone units (Elkhart just released a good one from everything I've seen) and built-in meters, typically with a foam pump. Some foam pumps are capable of showing discharge volume without flowing foam, others are not. If you don't have a foam pump with flow meter capability, I would suggest calling around and finding someone that has a stand-alone meter that is willing to come do some testing for/with you.

    Comment


    • #3
      There have been pump operators who figured that if the nozzleman's feet were still on the ground, he could throw a couple more pounds on the guage...

      I'll second what dfelix wrote, and note that it's beneficial to maintain a certain standardization to one's hose. That's a handy part of crosslays - you have a start point for pressure for the various loads.

      A variable we face is that we load our crosslays with the leadoff 100' being one 100' length vs two 50' lengths. It's not a big difference at the nozzle, but it's not exactly the same either, with the extra/missing coupling.

      An important note on automatics - your pump operator may be on top of his game and have sufficient pressure delivered to the nozzle based on all the variables. But if the nozzleman has the automatic throttled back...

      As for 130 PSI vs 135 PSI, the question is - is enough water ending up on the fire? Nothing else really matters.
      Opinions my own. Standard disclaimers apply.

      Everyone goes home. Safety begins with you.

      Comment


      • #4
        someone correct me if I?m wrong but I?m pretty sure the answer is no you can?t do that because because you always need to know the flow rate to find the nozzle pressure, and you need the nozzle pressure to find the flow rate. The change in discharge pressure changes both the flow rate and the nozzle pressure. Like these guys said, you?d need a flow meter or a pitot to plug some empirical data in.

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        • #5
          All makes sense. Thanks folks!

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          • #6
            If one had a Combi nozzle, would the nozzle discharge pressure be the same for the smooth bore and the fog? Or would the mechanics of the fog nozzle knock down pressure?

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            • #7
              Originally posted by Ctuttle3d View Post
              If one had a Combi nozzle, would the nozzle discharge pressure be the same for the smooth bore and the fog? Or would the mechanics of the fog nozzle knock down pressure?
              Fog nozzles can be purchased to operate at different nozzle discharge pressures. 20 years ago most fog nozzle operated at 100 psi, but more recently they can be purchased to operate a given GPM at 50, 75 or 100 psi depending on what you purchase or some even have two positions.

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              • #8
                Originally posted by RFDACM02 View Post

                Fog nozzles can be purchased to operate at different nozzle discharge pressures. 20 years ago most fog nozzle operated at 100 psi, but more recently they can be purchased to operate a given GPM at 50, 75 or 100 psi depending on what you purchase or some even have two positions.
                Which means you have to know the specs on the nozzle. I would suppose there are those that would say a nozzle is a nozzle is a nozzle, but....

                If it's a nozzle you've had in your inventory for a while, it could take some digging, unless someone wisely saved that information when the nozzle was acquired.
                Opinions my own. Standard disclaimers apply.

                Everyone goes home. Safety begins with you.

                Comment


                • #9
                  Originally posted by tree68 View Post

                  Which means you have to know the specs on the nozzle. I would suppose there are those that would say a nozzle is a nozzle is a nozzle, but....

                  If it's a nozzle you've had in your inventory for a while, it could take some digging, unless someone wisely saved that information when the nozzle was acquired.
                  Most that I have seen (fog nozzles) are either 100 psi or have some sort of marking with the rated nozzle pressure. At worst you should be able to Google the model number and get the specs fairly easily?

                  I happen to know that we have Many Elkhart SM-20F nozzles in the engineers compartments, a quick Google search reveals a spec sheet with all the gpm flows at various nozzle pressures, with the 100 psi highlighted in red as that was the intended target.
                  Last edited by RFDACM02; 03-11-2019, 09:52 PM.

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                  • #10
                    Originally posted by RFDACM02 View Post

                    Most that I have seen (fog nozzles) are either 100 psi or have some sort of marking with the rated nozzle pressure. At worst you should be able to Google the model number and get the specs fairly easily?

                    I happen to know that we have Many Elkhart SM-20F nozzles in the engineers compartments, a quick Google search reveals a spec sheet with all the gpm flows at various nozzle pressures, with the 100 psi highlighted in red as that was the intended target.
                    We have Combi Nozzles that the fog spec is 135GPM @ 100 PSI and when the bail is pulled all the way back they are a 15/16 smoothbore. If I have a nozzle pressure of 100 PSI when its being operated as a smooth bore, would I have 100 PSI if it were being operated as a fog? or would the mechanics of one vs the other knock the pressure down at the nozzle?

                    Comment


                    • #11
                      Without knowing the exact nozzle you are talking about, the safe answer is to either contact the manufacturer (Akron, I assume?) or to Google for that specific nozzle and see what you find. That's all assuming it's not printed on the nozzle somewhere.

                      Just to muddy the waters further, the new Elkhart Chief XD's have the capability of an integrated smoothbore in the shutoff, the 15/16" integrated is rated at 185 gpm @50 psi, a spin on fog bumper is rated for 175 gpm @50 psi for the same shutoff... It's all going to be nozzle specific, and many times it varies from nozzle to nozzle in the same model line depending on how it was ordered/spec'd.

                      Comment


                      • #12
                        We have Akron Saberjet 1533, I've found some information on it.

                        Do any of you know of a book, website, or someplace else I can go to learn as much as possible about fire ground hydraulics as a whole? I feel its something that in today's fire service is under taught and I'd like to learn as much as I can and teach my guys........ Thanks!

                        Comment


                        • #13
                          Originally posted by Ctuttle3d View Post
                          We have Akron Saberjet 1533, I've found some information on it.

                          Do any of you know of a book, website, or someplace else I can go to learn as much as possible about fire ground hydraulics as a whole? I feel its something that in today's fire service is under taught and I'd like to learn as much as I can and teach my guys........ Thanks!
                          I searched for "fire ground hydraulic books" and found several listed. They're in the $80-100 range.

                          Ditto for "fire pumper books."

                          "Fire hydraulics" will bring up a number of articles from various fire publications that may prove useful.
                          Opinions my own. Standard disclaimers apply.

                          Everyone goes home. Safety begins with you.

                          Comment


                          • #14
                            Originally posted by Ctuttle3d View Post
                            We have Akron Saberjet 1533, I've found some information on it.

                            Do any of you know of a book, website, or someplace else I can go to learn as much as possible about fire ground hydraulics as a whole? I feel its something that in today's fire service is under taught and I'd like to learn as much as I can and teach my guys........ Thanks!
                            The two I reach for:
                            Fire Service Pump Operators Handbook, by Warren Isman
                            Fire Stream Management Handbook, by David Fornell

                            But having the specs of your nozzles is important and more important than ever now with the number of options. Wasn't too long ago there were but two options for handline nozzle pressures.

                            Comment


                            • #15
                              As someone else has said above: The answer to your question is complex because there are two variables acting in the hose and nozzle system. Both are dependent upon the quantity of water flowing in the system, but the variable that you are trying to use is the engine discharge pressure. When I was introduced to the idea of operating a pump, the only text worth while was from a class at The City College of New York and taught by the author of the text. John Jacob Theobald who taught classes for the FDNY using his book "Hydraulics for Firemen". I still have a copy given to me by my Chief that was the second edition and published in 1947. A lot has changed, and while Theobald can be used, there are much more accurate mathematical equations that give more accurate answers to your questions. Every one of these equations, while fairly accurate, are only estimates of friction loss, nozzle flows, engine pressures and nozzle reaction with water flowing. On top of these variables is the newer nozzle designs, some of which "automatically" adjust to maintain a mostly fixed nozzle pressure. The designed operating pressure may be fixed, semi-fixed, variable, or set by the operator. The easiest nozzle to understand is a solid bore nozzle with a smooth tapered throat that minimizes turbulence. Think old style play pipe. The flow from the opening is determined by the diameter of the opening and the water pressure at the base of the nozzle pushing the water out of the opening. You can calculate this flow from the nozzle pressure using this formula: Flow = Q (quantity) = 29.87 x d squared x the square root of the nozzle pressure in PSI. Q will be the gpm, and d is the diameter of the nozzle opening in inches. Suppose we have a 1" diameter tip on a 2 1/2" play pipe. We have placed a gauge at the base of the nozzle and know that we are exactly 49 psi. What amount of water is flowing from that nozzle? Using a hand calculator you should be able to calculate a flow of 209 gpm. Try this equation a second time and find the flow from a master stream device at a pressure of 80 psi and a nozzle diameter of 2 inches. (1069) If we were to use an older style fog nozzle, we know that it will flow its rated gpm, if and only if we can hit the 100 psi of nozzle pressure required. Let us use an Akron Turbojet with the adjustable ring set at 250 gpm. If you hit the 100 psi correctly we will have the 250 gpm flowing, but what if we under pump so that the nozzle (set at 250) is only at 81 psi?? To use our formula, we must know the equivalent size of the nozzle that matches the 250 gpm fog nozzle at 100 psi. Use the formula by entering the 250 gpm as Q, the nozzle pressure as 100 psi and calculate the equivalent size of the solid bore opening. (Should calculate to 0.915 inches) Now we can use that opening as if it were a solid bore diameter and recalculate the flow using 81 psi as the nozzle pressure. ( Should calculate to 225 gpm) What is the equivalent size of the turbojet with the ring set to 160 gpm ?? Lastly we come to a TFT automatic nozzle that supposedly maintains 100 psi of nozzle pressure but changes the equivalent size of the opening by opening or closing the baffle plate to maintain 100 psi of nozzle pressure. Ask yourself, "What controls the water flow, if the baffle can move freely on its own to maintain 100 psi nozzle pressure?" Let us say that we are using 200 ft. of 1 3/4" hose that the friction loss table says has 35 psi loss per 100 feet at 150 gpm. Proper engine pressure would be 170 psi, and result in 70 psi of friction loss (35 lbs per joint) and 100 psi of nozzle pressure. What if the pump operator only throttles up to 125 psi? By looking at the friction loss table for 1 3/4" hose at a loss of 12.5 psi ( one joint or 25 psi in 2 joints) you should find a flow of about 90 gpm. So you should now be able to understand that the friction loss is going to determine the flow from an automatic nozzle. Generally a formula that relates friction loss and flow follows this form Fl = K x Q x Q x L where Fl is the friction loss in psi, K is a constant that is related to the hose size (diameter), Q is the flow in 100's of gallons per minute, and L is the number of 100 ft. sections. Three inch diameter hose with 2 1/2" couplings has a constant K of about 1, so if we were to flow a single line of 3" supply hose between engines at a flow of 400 gpm and we had 800 ft laid out, the pressure loss would be: 1 x 4 x 4 x 8 = 128 psi. If we needed to supply 500 gpm through the lay, what friction loss would we need to overcome? Fl = 1 x 5 x 5 x 8 or ( ? ) psi. If we are able to use 6" supply line for the entire 800 ft lay (K for 6" is 0.032) what will be the friction loss at 500 gpm ? If we needed to supply 2,000 gpm, what would the friction loss be? It should be obvious that if you double the size of the hose line (3" to 6") the loss decreased by 32:1. and that matches almost exactly the Hazen-Williams formula for pressure loss in pipe. Piping design engineers know that a 90 degree elbow causes an increase in pipe friction equal to about 15 additional feet of pipe. Take the time to look inside your pump panel and count the number of elbows from the pump manifold up to the Chicksan Swivel (2 90's for the swivel) and you could well have the equivalent of 60 or 75 feet of pipe right inside the panel. add to that the 200 ft. of preconnect, and you can easily have 180 to 200 psi of engine pressure to deliver 150 gpm on a 1 3/4" preconnect with an automatic nozzle. If you have followed this long post to the end, you should now understand that the pump pressure minus nozzle pressure is friction loss so in your first question where the difference was 56 psi, then 1 section would cause 28 psi of friction loss. A friction loss table for 1 3/4" hose says that you are flowing 135 gpm, but if Ep is 130 then there is only 15 psi loss per 100 ft, so the flow is now 98 gpm. This is well under the minimum recommended attack flow for structure fires. Your second question is a bit more complicated, but it is possible to derive a single equation that would combine both variables. For my part, I would try several iterations and a guess. Dropping the nozzle pressure to 50 and calculating the flow gets you at 180 gpm, then using the flow of 1.8 through a hose with a K of 12.5 yields 81 psi through 200 ft. Almost an exact match. Hope this helps more than it confounds.

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