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Hydrant outlet Q

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  • Hydrant outlet Q

    We had hydrant training last night and it made me wonder something... one of the teams instead of using the 4" output on the hydrant, used an adapter to hook the 4" supply line to a 2.5" discharge. What's the difference in flow between the 2... I argued that even with a 4" line, you're restriced by the 2.5 inch orifice of the hydrant... a bunch of the physics and engineer types thought it was neglible... I quickly shut up, but wondering if they're right?

    What's the flow with a 2.5" hydrant output adapted to flow through 4" hose?
    What's the flow with a 4" hydrant output to flow through 4" hose?

  • #2
    There are some real Numbers Guru's whom I suspect will be through shortly to answer your question, however from my foggy memory of Fluid Mechanics about 12 years ago - they are correct - the overall loss from the Discharge & adapter is negligible compared to the friction loss of the 4" hose.
    Take Care - Stay Safe - God Bless
    Stephen
    FF/Paramedic
    Instructor

    Comment


    • #3
      Simple answer (I hope)

      It appears that there is some confusion in the question at hand between friction loss and flow (GPM).

      You are right. The 2.5" outlet converted will not provide the same GPM.

      GPM is a function of opening diameter and velocity (pressure). To get the exact flow from each outlet of your hydrant you will need to test that specific hydrant. This can be done with a Pitot gauge (or any other flow testing gauge out there) and a flow chart. You should see that the larger opening flows more water.

      A smaller diameter opening will not be able to provide the same amount of water as a larger opening at a given pressure. A chain is only as strong as its weakest link. Attaching a 4" hose will not increase GPM coming from the 2.5" outlet.

      Try it here: http://www.flowcalculator.com/

      Assume the pipe is full, velocity is constant for both so that can be any number you like. Try different diameters and see what GPM you get.

      Hope I helped at least a little. Maybe someone a little more educated can shed some more light on this complex subject.

      Rob

      Comment


      • #4
        You are right that it will restrict flow, but the 2.5 port will still allow more than enough flow to allow the 4 inch to perform well (and far better than a 2.5 inch hose). Although it seems counterintuitive, both 4 inch hose, and a 2.5 inch steel port are capable of flowing up to 2000gpm with adequate pressure. The 4inch steel port alone can actually flow much, much, more than 2000gpm, but again, the 4 inch hose is the restriction.

        Even on hydrant pressure, you still get much more than the flow capacity of 2.5 inch hose through the smaller port. The friction loss of 2.5 inch hose is significant, while the steel port has effectively no (or negligible) restriction other than the total volume limit.

        The other advantages to using the 4 inch with adaptor are:

        1. Consistency - For the small department that may put rookies on hydrant duty (like us), why advocate numerous scenarios and introduce possibility of mis-deployment of supply, when one hose size can be used in almost all scenarios.

        2. Capacity - You will still flow more through one 2.5 port and 4 inch LDH, than 2x2.5 inch ports with a 2.5 inch hose on each.

        3. Friction Loss - Regardless of what you are flowing, there is negligible friction loss in 4 inch, compared to moderate loss in 2.5 inch. You can flow up to 600gpm through 4inch before you get the same friction loss as 2.5 inch hose at 200gpm. You can get much longer lays out of it in any scenario.

        And remember that you can flow the capacity of 4 inch hose out of a single 2.5 inch pump discharge too, so if you are relay pumping, you can use an adaptor directly into the big stuff to virtually eliminate friction loss and reduce the workload of the pump.

        To find the max volume capacity of a steel discharge use this formula.

        GPM = 29.7 x d2 x /N

        Where:

        GPM - Gallons per minute
        29.7 = your constant
        d2 = diameter in inches, squared
        /N = square root of discharge pressure in psi

        So the max flow capacity of a 2.5 inch steel port at 50 psi is 1312.57gpm, at 100psi is 1856.25gpm
        The max flow capacity of a 4 inch steel port at 50 psi is 3360.2gpm, at 100psi is 4752gpm

        Both are far more than the flow capacity of hose due to friction loss. To calculate your real-world flows, you must perform a flow test on your hydrants.

        For more info, see page 16-18 of this tech sheet to see a chart on flow capacity of a 2.5 inch discharge at various pressures.

        http://www.goulds.com/pdf/ttechwp.pdf
        Last edited by mcaldwell; 06-09-2006, 08:07 AM. Reason: mi stewpid speling misstaks
        Never argue with an Idiot. They drag you down to their level, and then beat you with experience!

        IACOJ

        Comment


        • #5
          We had several long discussions on this topic about 6 months ago and I, and some others, ran some tests. Bottom line is LDH hooked to the steamer gets you the best flow obviously, but if the steamer is unavailable for whatever reason, LDH on a 2.5" is much, much better than 3". As stated the short length of restriction is quite significant but you can still get a lot of water through it.

          Water system pressure has a lot to do with this. A water system that has 80 psi pressure on it is going to force a lot more water through that 2.5" into the LDH than a water system that has only 30. Even if the 30 psi system is capable of flowing 2000 GPM through the steamer port into LDH, it might not flow very good at all through the 2.5". The 80 psi system will do better in that case. Depends on if you have tanks on hills or water towers and pumps, etc.

          Birken

          Comment


          • #6
            OK, Where's The Spotted One??.............

            Calling Dalmation90, report to the Hydraulics Debate!!.......

            Dal has his act together on things like this, so when he comes along, you should get a scholarly answer. I can't add anything because we NEVER (Yes, I said Never) connect a Supply Line direct to a hydrant, There is ALWAYS (yes, I said always) an Engine on the hydrant to pump the line. We normally connect a 20'x6" Soft Sleeve to the hydrant, but if the 4.5 port is not useable, we put a section of 3 inch on BOTH 2.5 ports. I can usually get 1,000 GPM that way. Our hydrants range from 1,000-1,500 GPM up to 3,000 plus GPM, depending on the grid that the main is fed from. One hydrant that we use for drills runs 125 psi static, and drops to 90 psi at a flow of 2,000 GPM.
            Never use Force! Get a Bigger Hammer.
            In memory of
            Chief Earle W. Woods, 1912 - 1997
            Asst. Chief John R. Woods Sr. 1937 - 2006

            IACOJ Budget Analyst

            I Refuse to be a Spectator. If I come to the Game, I'm Playing.

            www.gdvfd18.com

            Comment


            • #7
              Whew... not sure if I'm more or less confused than before, but there sure is a LOT of good info here. In the scenario we were performing, they were using a 2.5" outlet on the hydrant adapted to 4" supply into a 4" steamer on the engine, and then pumping 2 3" supply lines to the attack engine.

              My argument was we have the capability to use the 4" outlet on the hydrant, and that we should to get the most possible water out of it. It sounds from the above responses that I may be partially right? Our water supply guru (also a retired engineer) doesn't seem to agree.

              Comment


              • #8
                Originally posted by Firetacoma1
                In the scenario we were performing, they were using a 2.5" outlet on the hydrant adapted to 4" supply into a 4" steamer on the engine, and then pumping 2 3" supply lines to the attack engine.
                I think the bottleneck in the above is the two 3" connections. While you will get more flow from the 4" discharge then the 2.5" discharge on the hydrant, both will flow more then your 2x3" will allow
                So you call this your free country
                Tell me why it costs so much to live
                -3dd

                Comment


                • #9
                  Calling Dalmation90, report to the Hydraulics Debate!!.......

                  At 14:00hrs something on Wednesday, during a gusty storm, I lost Cable TV / Internet to my home (and thus home office).

                  22:00hrs TV was restored, but apparently the parts to repair broadband were shipped on the slow boat from China. So I write this from a cafe, 48 hours after the outage began

                  The friction loss of an 2.5" outlet is negligible compared to the whole system. If I'm moving water, I'd much rather have a 4" on an 2.5" outlet, then a 2.5" hose on a 6" steamer outlet If I'm just filling a tank, I don't really care.

                  Let's look at the fundemental question:

                  "What's the difference in flow between the 2... "

                  The answer is...it depends.

                  First, it depends on the overall volume the hydrant can provide.

                  Second, it depends on the residual pressure while flowing that volume.

                  Let's take a hydrant that can provide 1500gpm @ 20psi residual pressure, which is the lowest the water departments like you running the residual.

                  Using the formula for solid bore nozzles, it takes an orifice 3.4" in diameter to deliver 1500gpm @ 20psi.

                  Indeed, at 20psi, a 2.5" will only flow about 850gpm.

                  NOW, something will happen between those two extremes -- almost all hydrants that can flow 1500gpm @ 20psi will increase their pressure as flow reduces. So that same hydrant may provide 1050gpm @ 30psi, which will deliver full volume through a 2.5" outlet. How various flows & associated residual pressures is affected is something you need to figure out based on your actual hydrants -- I know once you have several data points, there are calculations to estimate out the range of options, but I've never really played with them.

                  If we go on "We have really, really great residual pressure" systems, 1500gpm @ 60psi will flow that full volume through a 2.5" orifice.

                  Now also keep in mind the affects on the whole system during a major fire.

                  A system that can supply, say, 4500gpm @ 20psi will probably be able to deliver 1500gpm @ 60psi through a single 2.5" if that's the only hydrant in use. But as other hydrants are hit and your residual pressure goes down, the flow in that outlet will go down as residual drops below 60psi.

                  If you've developed SOPs based on a just using a single hydrant for an incident, you could have some head-scratching going on as master streams are screaming for water during a large incident.

                  Or that 1st due Engine that thought it had a small fire and just forward laid in a 3" line from a 2.5" outlet could find itself in a world of hurt as it's intake pressure keeps dropping as more and more hydrants are hit -- dropping the residual pressure that's needed to push a given volume through the hydrant's 2.5" outlet, then all that 3" hose.

                  So, hopefully I've made it clear as mud There's really no one, universal answer -- but it is a question that can be answered for any specific situation fairly easily if you know all the details.

                  Comment


                  • #10
                    So... is that a maybe?

                    Would you rather have a 4" on a 4" steamer, or a 4" on a 2.5" discharge?

                    Comment


                    • #11
                      Originally posted by voyager9
                      I think the bottleneck in the above is the two 3" connections. While you will get more flow from the 4" discharge then the 2.5" discharge on the hydrant, both will flow more then your 2x3" will allow
                      You can move a hell of a lot of water through 2x3" after the pump, as the pump allows you to control the residual pressure and maintain maximum flow capacity. I am sure you will meet the capacity of even one big engine with that setup, assuming you are getting the volume into the first truck to begin with.

                      But having said that, a single 4" between the engines will flow the same amount with lower friction loss. Each inch of increased diameter in a given hose roughly doubles the flow, so a 4" hose flows twice as much as a three inch hose (or as much as two 3 inch hoses).

                      The downside to the 2x3" setup is each 3 inch hose has significantly more friction loss than the single 4", a longer lay of 3 inch will see the flow reduced more so than the same lay of 4 inch.

                      The downside to the 4 inch, is that it's operating pressure limit is usually around 175 psi, with a test max of 250 (higher pressure 4 & 5 inch is available). The 175 is not usually a problem unless you are pumping waaay uphill, or expect some water hammer from a sudden shutdown at the attack engine.


                      I also love working with 4 inch. Storz fittings, no way to get it backwards, and easy rinse and load after the fire. While I will still pull the small stuff for trash fires, etc. I would rather pull 4 inch over 2.5 or three inch any day. I know I have the flow I will need, and it is often quicker in the end.
                      Last edited by mcaldwell; 06-09-2006, 03:47 PM.
                      Never argue with an Idiot. They drag you down to their level, and then beat you with experience!

                      IACOJ

                      Comment


                      • #12
                        Originally posted by Firetacoma1
                        So... is that a maybe?

                        Would you rather have a 4" on a 4" steamer, or a 4" on a 2.5" discharge?
                        Dalmation190's answer means there are multiple variables to take into consideration which is very dependant on the actual flows of the water system.

                        There is not a real clear answer. It would be like saying all fires are the same. They all depend on what is burning so they are different.....but they are all fires.....

                        Rule of thumb answer is what you are looking for I think: If it has a steamer us it... otherwise use the 2.5".

                        Technical answer: See Dalmation190's post.

                        Comment


                        • #13
                          Originally posted by Firetacoma1
                          So... is that a maybe?

                          Would you rather have a 4" on a 4" steamer, or a 4" on a 2.5" discharge?
                          I think he is saying option B (4" on 2.5 Discharge), but you cannot calculate the exact flow without knowing your system.

                          And I agree because Dal is always right when it comes to hydraulics.
                          Never argue with an Idiot. They drag you down to their level, and then beat you with experience!

                          IACOJ

                          Comment


                          • #14
                            Errr...

                            Using the steamer will always give you the maximum flow for a particular layout (hydrant, pump, appliances, etc.)

                            HOWEVER

                            That is not necessarily the only correct answer.

                            In certain circumstances, you could be limited by other factors -- either on the hydrant side, or your layout (appliances, pumper, hose, etc) -- that means the maximum you will flow is still achievable through the 2.5" on the hydrant.

                            WHAT other factors we don't know is how your resident experts are deriving their opinions. If it's simply from a class taken 30 years ago, it might be suspect. If it's from that class...combined with years of experience with local operations and knowledge of how things work locally it could very well be true in a local situation you get the same flow in the same situation regardless of using the steamer or 2.5".

                            Perhaps the only true answer is wait until you're a company officer and can take the the truck and crew out for a drill and play with the flows yourself

                            I can also see situations in a drill where you might want to use a keystone valve* on a 2.5" discharge going to a 4". It's certainly easier / quicker to close and open the keystone then to close & open the hydrant itself -- so that might be an advantage if teaching or practicing on something that isn't really about hydrant operations.

                            ============
                            * Keystone = 2.5" Gate Valve...since apparantly I come from one of the few fire departments in the world that calls a Keystone Valve a Keystone Valve

                            Comment


                            • #15
                              Originally posted by Dalmatian190
                              I can also see situations in a drill where you might want to use a keystone valve* on a 2.5" discharge going to a 4".
                              Isn't that also known as a "fully dressed" Hydrant?
                              So you call this your free country
                              Tell me why it costs so much to live
                              -3dd

                              Comment

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