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  • hydrant flows

    There is a disageement in my dpt. I was hoping someone could clear up. If you put a pitot flow gauge on a 2 1/2 outlet and flow it, can you use the chart to convert this reading to gpm rating for that hydrant, or do you need to have the static and residual pressures? Thanks

  • #2
    You would get a flow that applies only for that specific pressure. It is better to have all three figures (static, flow & residual pressures) to have an accurate picture of the volume available from the hydrant. The fire service software we use requires all three figures and computes the flow available at whatever residual pressure you specify.

    You can also graph the pressures to get an idea of flow at different pressures.

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    • #3
      Why wouldnt the flow at that specific pressure be good enough. Would it fluxuate enough to actually make much of a change?

      Comment


      • #4
        Flow pressures can vary by a large amount depending upon the time of year, day of the week, and hour of the day. Residential areas normally will have a lower flow pressure when people are watering lawns etc. Retail and industrial areas will normally have a lower flow pressure when they are open for business.

        Ideally you should also do area flows for complexes using at least two hydrants to get an idea of total water available for high demand.

        Many small communities in our area and water districts do most of their pumping to fill storage tanks at night. As a result flows can vary from 800 to 1200 gpm in our district based on the level of water in storage. For example, a flow of 20 psi through a 2.5'" outlet will give you approximately 830 gpm. Raise the flow to 30 psi and you get approximately 1025 gpm.

        Remember there are several reasons to conduct hydrant flows.
        1. How much water is available and how much reserve.
        2. Check hydrant for proper operation.
        3. Identify any significant change from previous flows. We often find that the water people close valves to do work on mains and forget to open them fully if at all. If the hydrant flowed 1000 gpm and now flows only 400 gpm, you have a problem somewhere.
        4. Flush the water system.

        NFPA and IFSTA pubs have a lot of info on water systems. They can explain thing a lot better than I.

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        • #5
          OK. That makes sense. I have read a lot of info on the net about the proper way to do a hydrant check. Most say you need to get the residual pressure at 20 psi. Why? If the residual pressure is higher than that, why wouldnt the flow be higher?

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          • #6
            We often find that the water people close valves to do work on mains and forget to open them fully if at all.
            I got hold of a report of the hydrants in our area and passed the info onto the Chief. He immediately contacted the water works dept. reguarding some questionable flows. Sure enough there was valves half open. The problems were corrected within minutes.
            Just one man's view from the flames.

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            • #7
              LT334
              Testing a hydrant for flow is not complex and as Ray R has pointed out the ISFTA and other manuals do a good job of listing procedures for conducting a good flow test.

              Here goes: determine what hydrant you want to test. If you are pre-planning a target hazard the hydrant closest to the hazard should be the hydrant that you want to test. Using a 2 1/2" outlet attach a cap with a pressure gauge attached. Keep all other outlets on that hydrant closed. Open the hydrant. Take the Static reading. Proceed to the next down stream hydrant, leaving a person at the test hydrant. Take off one outlet and determine the type and size of that outlet. Open this "flow" hydrant and using the Pitot tube take the flow pressure and record that. The person at the test hydrant will then take the "residual pressure" reading.

              Because the size and type of opening is known and the "flow/velocity" of the water is know the gpm can be determined. With the residual pressure taken from the test hydrant, a point can be determined given gpm and pressure. Compare that to a zero gpm with a static pressure and a comparison can be made since there is a relationship between flow, pressure and orifice size.

              This information can either be entered into the computer program that Ray R spoke about or you place this information on special graph paper that when the flow/pressure points have been properly placed, will provide a straight line that can be extrapolated to a residual pressure of 20 psi. You need not get the pressure down to 20 psi when flowing the "flow" hydrant.

              Let me know how you do. E-mail me for more info.

              Comment


              • #8
                Hosekey21,
                That's great. That's what this whole internet thing is supposed to be about.

                We had a similar experience. I was having a long standing conversation with one of our local water companies regarding an area in our first due that was at best 1250 gpm at 0 psi. (yes, the engine was close to cavitation, but the fire required more flow than was being provided) They claimed that the flow should be closer to 2000 gpm. This was important since this is a heavy industrial area.

                Further investigation by them indicated that a valve upstream was almost closed. They located the valve and opened it fully. We now have 2000 gpm.

                Any fire department that does not routinely test fire hydrants for flows or at least gets flow tests from water utilities are setting themselves up for a major loss.

                Work with your water utilities or departments and make sure that when necessary they can respond to fires and help you solve your water supply problems. Try to develop that relationship so that when developers start to develop an area that your department has enough water to fight the fire that will surely come. Make the developers foot the bill for water system improvements.

                Just my two cents and that won't even buy one.

                Comment


                • #9
                  tHANKS A LOT, THAT HELPS A BUNCH. wHAT IF THE HYDRANT YOU ARE TESTING IS AT THE END OF THE WATER MAIN AND YOU HAVE NO DOWNSTEAM HYDRANT TO FLOW?

                  Comment


                  • #10
                    LT334,
                    Put the gauge on the second to last hydrant and flow the last one. Won't give you the most accurate but that's the best you can do.

                    Putting the gauge on the last hydrant and flowing the upstream hydrant won't do any good.

                    Remember that just because there's great pressure on the hydrant in a static condition doesn't mean that these's good water. GPM puts out fire, not PSI. The only way to determine GPM is to do the flow test and crunch the numbers.

                    Also if you've done what I suggested in my earlier post and you have dead end hydrants make developers loop the main to some other area or water source. As long as it's the same quality of water (potable) then water coming from two different directions should be better than one.

                    Good luck.

                    Comment


                    • #11
                      When I test hydrants for supression purposes I flow test the port on the hydrant that I am going to hook my supply line to. If I am laying duals I will flow both ports together. The tests that are being discribed by others in this thread are accurate in telling how much is available in the mains however if I can't get it out of the hydrant through the port and supply hose than it doesn't much matter how much water is available.

                      Comment


                      • #12
                        The tests descrbed are accurate, what is in the main doesn't matter, ... eh?

                        What is missing in the fire service is firefighters simply saying I don't know instead of trying to BS there way through everything they don't fully understand.

                        Now some answers, any pump operator was supposed to know this stuff if he is worth his salt.

                        1. Dead end main. Flow test the end most hydrant and use a gauge off a house spigot to get the static is the by the book, exact way to conduct the test.

                        2. What is in the main doesn't matter if I can't get it out of one hydrant? So, I am to understand yo that you are hooked to a hydrant that will flow 2000 gpm attached to a water main that will flow 24,000 gpm and you wouldn't want to go right and left of that hydrant on the same main and use the water????? Sheesh...... Main tests tell you what is going to happen to your 2000 gpm hydrant when all your buddies hook to it. The flow test you showed is on;y realistic if that is the only hydrant you are going to use on a fire. Whereas an area test will tell you that 2000 gpm hydrant isn't really a 2000 gpm hydrant and should be counted as such.

                        3. As you can clearly see there is a difference in pressure.

                        4. There is no reason to loop all dead ends mains, simply follow NFPA and AWWA and the dead end will be the right size to do its job...in other words follow the whole code.

                        5. The book might say test at 20 psi residual but would you really leave 60 to 150% of your water in the ground the day of the fire? 20 psi is the minimum...residual. If you use 4" hose you are going to want to have a residual 3 times higher than a guy using 5" hose, and 3 inch users unless you like relays will need a residual 21 times higher than a guy using 5" and the 2 1/2" USERS WILL WANT 52 TIMES MORE RESIDUAL. You'all know the 20 psi is based upon hooking the pumper up to the hydrant directly in a reverse lay not a forward lay. The guy using 4" hose will need three pumpers in relay, the 3" user will need 21 and the 2 1/2" user 52 to do the same job as a 5" line.

                        6. Flow a hydrant on each side of your static hydrant anything less isn't a valid test.


                        You know, if your going to speak so matter of fact, at least be right.

                        FINALLY, shall we discuss how useless multiple fire truck relays are???

                        Comment


                        • #13
                          play, or is it larry?
                          What he was asking for is whether he needed more than a flow/pitot tube reading or not to determine the available flow rate in a hydrant.

                          While most of the fire service is satisfied to get the information that comes from the test that I described, you have to confuse the issue and get hose size and other useless information involved.

                          If this is larry, why do you have to prove to everyone that you know more than everyone else? Is it because your so insecure in other areas?

                          Comment


                          • #14
                            LET'S TRY A MONGO for am/fm

                            ...What he was asking for is whether he needed more than a flow/pitot tube reading or not to determine the available flow rate in a hydrant.

                            ACTUALLY HE ASKED "If you put a pitot flow gauge on a 2 1/2 outlet and flow it, can you use the chart to convert this reading to gpm rating for that hydrant, or do you need to have the static and residual pressures? "

                            Wouldn't the correct answer be, The answer is you can get good info either way RIGHT?

                            Yes!

                            If he was going to make a forward lay, isn't his method more accurate than you converting to 20 psi?

                            Yes.

                            AND THEN HE ASKED "Why wouldn't the flow at that specific pressure be good enough. "

                            It would be fine for practical application, right?

                            Yes.

                            Your 20 psi residual is not practical, right?

                            Yes.

                            THEN HE SAID, "I have read a lot of info on the net about the proper way to do a hydrant check.

                            You can't support your method using AWWA or NFPA now can you?

                            NO!

                            THEN HE SAID, Most say you need to get the residual pressure at 20 psi. Why? If the residual pressure is higher than that, why wouldn't the flow be higher? "

                            The answer is Yes it would be higher, more practical, and will be accurate in a forward lay.

                            AND THEN HE SAID, "wHAT IF THE HYDRANT YOU ARE TESTING IS AT THE END OF THE WATER MAIN AND YOU HAVE NO DOWNSTREAM HYDRANT TO FLOW? "

                            And someone gave him a bull crap answer that could not be supported by AWWA or NFPA, right?

                            Yes.

                            Oh that was you spreading "worthless information" right?

                            Yes.

                            In fact you said, "Won't give you the most accurate but that's the best you can do. "

                            That is completely wrong, right?

                            Yes.

                            Just admit it, you don't know how to conduct a dead end main test, right?

                            Yes.

                            Then you said, "The only way to determine GPM is to do the flow test and crunch the numbers."

                            That is wrong too, isn't it?

                            Yes!

                            AWWA and NFPA suggests other methods as well modeling, diameter and run, hydraulic calculation etc. Right?

                            Yes

                            am/fm, it seems he said a lot more than do you need static, flow and pressure readings, doesn't it?

                            YES!

                            It does not appear you make a real good case does it?

                            No.

                            Then yo said,"Also if you've done what I suggested in my earlier post and you have dead end hydrants make developers loop the main to some other area or water source."

                            Do you live in utopia?

                            " As long as it's the same quality of water (potable) then water coming from two different directions should be better than one. "

                            That is not accurate either, right?

                            Right. A single 8 inch dead end will out flow any looped 4 or 6 inch system right? It isn't about looping it is about doing the math right the first time and following NFPA and AWWA to the letter not your good enough almost right answers, right?

                            Right.


                            ....While most of the fire service is satisfied to get the information that comes from the test that I described...

                            So looking at the Fire Protection handbook please tell me which illustration shows only flowing one hydrant?

                            THE ANSWER NONE. THEY ALL SHOW 2 or more flowing.

                            So most of the fire service does it half axed???

                            .... you have to confuse the issue....

                            With facts.

                            .... and get hose size and other useless information involved.

                            Gee pal, you suggested the 20 psi residual. 20 is fine if you always park the fire truck at the hydrant. Other than Detroit and FDNY who does that every single fire?

                            Worthless info???? You say 20 psi, yo told him how to determine the gpm. So 1000 gpm at 20 does not get you 1000 gpm with standard residential or commercial hydrant spacing with most hose sizes.

                            DOES IT????

                            No it does not.

                            ....prove to everyone that you know more than everyone else?

                            Obviously in this case he knows more than you! Lol

                            ....Useless information?????

                            YOu mean you just don't understand the practicalapplications suggested in plays post, do you?

                            Comment


                            • #15
                              Sorry, I didnt want to get a war started. I was hoping there was an easy correct way to answer my questions. I guess this subject is like every other one and open to interpritation. At least you guys can all be proud of the fact that someone is at least attempting to test your hydrants. no-one in my town is.

                              Comment

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