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4" or 5" LDH

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  • #16
    4" is best suited to medium flows off a modest hydrant system going a modest distance.

    5" will make the most of low pressure systems, take advantage of high volume systems, and move it the furthest.

    If you have a hydrants that put out 1000gpm at 65psi residual pressures and only lay 500', 5" ain't gonna do anything for ya other than *maybe* save a little bit of fuel since you're not boosting the pressure as much with your pumper If you have a hydrant that can deliver 2000gpm, you can get big flows but only with low residuals, or you have situations you need to lay a quarter mile or more...5" can make stuff happen without using relay pumpers or parrallel lines.

    The figures MG quoted are based on rubber lined, double jacketed hose which just about no one on earth runs in these diameters. Most modern supply lines have more flexible jackets (read: they expand in diameter under pressure) and slipperier liners which make a big difference.

    165psi PDP, 20psi residual, 1000gpm through Angus Hi-Vol will get you 1,600' in 4" and 3,300' in 5". Other brands will fall somewhere in between Angus which AFAIK still has the best performance and the "book" values.

    Will you necessarily get the whole 1,600'? Only way to find out is to pump your own hose and measure it. But it should be significantly more then the 725' value based on obsolete hose technology.

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    • #17
      Exactly Dal ...

      My point in my posts were that if you currently operate with 4", the additional amount of water you would flow with 5" are in all liklihood not worth the very large expenditure of switching over. This seems especially true especially in the original posters situation where hydrants are plentiful and generally spaced about 750' apart.

      A few simple additions or changes can be much more cost effective. The addition of a utilizing a (previously mentioned) 4-Way Valve can make a huge difference. This wikll allow a pumper to "boost" the 4" laid in by the first due pump without requiring the hydrant to be shut down to make the connections. In my previous department, where we used 4" extensivly, we were able to flow 1500 gpm or more off 20 psi hydrants 1000' when we utilzed a pumper at the hydrant. I would dare to say that a flow such as that will be more than sufficiant for 95% of the time for most departments out there. In addition, if in most cases, hydrants are within 750', a second line will not be a problem to lay quickly if even more water is needed.

      I understand the thought that we need to think about those 5% of our fires that will require very large flows. In this case, it seems like there are more than enough resources to deal with that 5% without completly re-hosing the fleet. After all it's not our money, but we do need to be smart with it.
      Train to fight the fires you fight.

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      • #18
        [QUOTE=Dalmatian190]

        The figures MG quoted are based on rubber lined, double jacketed hose which just about no one on earth runs in these diameters. Most modern supply lines have more flexible jackets (read: they expand in diameter under pressure) and slipperier liners which make a big difference.

        [QUOTE]

        Good point. Unfortunately you can't work strictly off of friction loss cards for true values with hose these days. It is true, though that "old school" values can still show the difference an inch makes in hose diameter.

        Thanks for the reminder...

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        • #19
          Originally posted by LaFireEducator
          Exactly Dal ...

          My point in my posts were that if you currently operate with 4", the additional amount of water you would flow with 5" are in all liklihood not worth the very large expenditure of switching over. This seems especially true especially in the original posters situation where hydrants are plentiful and generally spaced about 750' apart.
          MG+ Dal:Good points about the true measuring of friction loss, true PDP and the gains of 5" over 4".
          LA: I'd note the same principles hold true for 5" making it that much more useful. Anytime you can upgrade to push more water further, eliminating inline apparatus and pumpers on hydrants would seem to have a high potnetial for pay off. And the original poster does not seem to have the monetary constraints some of us share. So where's the downside?

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          • #20
            If they have the money, there really isn't a downside.

            However, given that they seem to have a pretty descent water setup at the moment, which can be made better with a rather small investment in a few 4-Way valaves and maybe the addition of an additional pump on the run card for the hydrant (if they don't have enough now), I'm just thinking that the money they would pour into a complete 5" upgrade could be better used on firefighter safety issues .. TICS, RIT equipmen, tgear, upgraded training, communications, etc, etc.

            But since I have no other info on them it's all speculation I guess. maybe none of that is an issue and the money is truly available.

            Just my thoughts.
            Train to fight the fires you fight.

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            • #21
              But investing in those 4 way valves also ties up an added engine. Where 5" may let them get the job done with 1 engine, the 4" and hydrant valves now requires 2 engines. Just an added thing to figure in that they may have the engine available, they may have to be waiting for it to come mutual aid, etc. Again, it's just another consideration.
              "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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              • #22
                We used 4" and we tried 5"- we only use 4" now

                Our department has used 4" LDH for years. We tried 5" on two engines for a 6 month period and based on the feedback from crews the department has decided to stick with 4". The flow calculations on paper look appealing for the 5" but in practice the 5" is very heavy. There can be more kinks in any given situation which contributes to friction loss. The actuall size of the hose lowered the length of hose we could store on our engines; so the benefit of being able to use the 5" LDH for long lays was not practicle.

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                • #23
                  So where's the downside?

                  There's very few.

                  5" does weigh more, both empty and charged. Might make a small difference if you're really watching your GVW (i.e. rural department and amount of water you can carry...).

                  Either charged needs some serious manpower -- around 6#/foot for 4" and 9#/foot for 5".

                  Similiar to the dry weight is the space per length issue mentioned by Firefloor.

                  In certain rural evolutions, you strand more water in the hose. For us a common evolution is to forward lay 500' to 1000' up long driveways. 5" takes 36 gallons more per 100' to charge than 4". May not sound like much, but you're losing it in those critical first few minutes when the booster on your first in truck is rapidly going down, you're in the middle of the active firefight, and most of your water is still responding lights-and-siren. In some situations, it'll mean the difference between the first ET pumping off giving you a couple more minutes of water v. just filling the line.

                  We do run both. However, I think that's largely a legacy of acquiring a good amount of 4" in a merger with another station. I'm not sure at all we would've spent money initially to split between 5" for supply and 4" for fireground otherwise. But given we had the 4", it was put to the best use.

                  NOW...

                  An equally valid question becomes...if you're department decides that 4" is perfectly adequate given medium flows, medium hydrants, medium distances...is there really any advantage to running 4" vs. staying with dual 3" lines? Given the same hose construction, they give equal performance. And give you several options -- laying only a single, easier and quicker to pickup supply line for outside fires; higher operating pressures if necessary; if one line is lost, you still have a supply; and for unusual situations being able to lay one very long supply line (recognizing the lower flows).

                  It's just to point out that you can select the right tools for how you operate. A pencil and calculator can help a lot, but sometimes then it becomes a judgement call among equal options which you prefer.

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                  • #24
                    Maximizing the hydrant

                    Our department dresses the hydrant with a gate on the steamer port and both 2.5" ports as well. The 4" supply is always utilized and in some situations a second supply line (2.5") is dropped with the 4".

                    So it seems we have found this adequate to date. We have fire calls in hi-rises in highly populated downtown areas and we have barn fires down 900' driveways.

                    Relay pumping has always been our way to achieve the volume and pressure we need.

                    Comment


                    • #25
                      One of the other issues with long lays is that generally these happen in less than urban places where the next due engine could be a few minutes. If you forward lay until your bed is empty then proceed in, how long before you've got water? Sure you can carry umpteen hundred feet of either hose, but once its charged who is gonna break a pumper inline when you need more water? In all likelyhood you're going to lay out the bed and put in a truck at that point. Now how far have you laid and what are you going to get for GPM at the end?

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                      • #26
                        RF ...

                        Your scenerio is another excellent use for a 4-Way Valve. The engine starting the lay (either forward or reverse, depending on the situation) simply leaves thier 4-Way Valve at the point thier bed is empty, or in the case of a lay up a driveway, at the point they start the lay at the road. The next truck in simply lays from the first engine's 4-Way valve, until his bed is empty, then he leaves his 4-Way at the end of his lay. If a third bed was needed, the 3rd pump would simply start his lay at the 2nd engine's 4-Way ..... etc. etc.

                        This allows water to flow the entire length of the lay once it is finally connected to the attack truck and the water supply is secured without a pumper (besides the supply pumper) in the relay, if they are needed elsewhere (such as in a supplemental tanker shuttle). It also allows pumps to be added as they become available (at in the case of my former department in Vt, 1100' intervals) without the water supply ever being shutdown. We used this system quite a bit, and using 4 Ways, laid as much as 4500' of supply line, adding pumpers as we went without ever having the shutdown the line.

                        By the way, I don't sell 4 Way Valves ... I just like thier practicallity!!!
                        Train to fight the fires you fight.

                        Comment


                        • #27
                          Originally posted by RFDACM02
                          One of the other issues with long lays is that generally these happen in less than urban places where the next due engine could be a few minutes.
                          Yep, this happens alot. Lay as much hose as is in the bed and have the next due engine/tanker supply you. If its 1300' of 5" then you set your limit of water flow somewhere around 1250 GPM using standard friction loss formulas. Thats only one effective deluge gun stream for a well involved fire. We know what the end result will be.

                          I would say the long ose lays dont happen as often in urban/hydranted areas, so when the need for water using longer relays comes up, it isnt as well practiced and understood. When 98% of the supply lays require less than 1000' of hose, its almost a sure bet that when longer lays are needed that you will end up with a very inefficient hose lay because the operators frequently arent well practiced and don't understand the hydraulics.

                          Its sad to say, but very true that many, if not most, of the engine co drivers out there are simply that..drivers that are trained to pull levers. If you don;t believe me watch how many operators will put water into the front bumper inlet and out the tailboard outlet trying to flow maximum water in a relay, while the 6" inlet and 5" outlets on the panels sit capped and unused.

                          I've seen a few departments in metro DC that have split 3" beds and a bed of 4 or 5" as well. Now you can lay a single 3, dual 3's, single 4, 4 and one 3 and 4 and two 3's. Lots of options. Laying all 3 (two 3's and one 4")lines equals the flow of dual 4" lines (thoretically calculated). Check out West Lanham Hills MD Engine 281:

                          http://www.wlhvfd.com/281_detail.php

                          http://www.wlhvfd.com/rigs.php

                          Consider national triple duty 4". it is rated at 300 PSI (285 realistically). We use it on one of our rigs. Having the high pressure hose gives us the ability to flow closer to the performance of a single 5" (standard pressure type) because it can be pumped at higher pressures. 5" is still better for high flows, nobody can argue that.

                          http://www.snap-tite.com/divisions/s...iple_duty.html

                          Snap Tite ATX also perofms similarly.

                          http://www.snap-tite.com/divisions/sh/atx.html
                          Last edited by MG3610; 09-19-2006, 12:38 PM.

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                          • #28
                            Here's another way to look at it.Why buy anything bigger than a 1000gpm pump if you're going to use 4"? Unless you have super short lays on really good hydrants you're not going to be able to efficiently supply that 2000gpm Engine unless you lay two 4"s.With the 5" however,it's a different story.As far as the weight per 100' goes,check with your mfg,the difference between 4 and 5 per hundred is negligable.I know because this is a arguement we have been fighting here on a local level.By October our Reel truck will have 3000' of 5" on it and the rest will have 5 to 4 adapters.Eventually I see us going to all 5". T.C.

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                            • #29
                              Does anyone still use 3 1/2" hose?

                              Mathmatically it seems like a very good size for Urban departments: that is departments with close hydrant spacing, many pumpers, and specialized equipment such as hose layers & unusual pumping apparatus.

                              A Wagon & Pumper with appropriately rated pumps and Dual 3" lines can only move:
                              2000 gpm 200'
                              1500 gpm 300'
                              1250 gpm 500'
                              1000 gpm 800'
                              A higher rated pump could push a bit further.

                              A Wagon & Pumper with Dual 3.5" lines can move these flows at double the distance of 3" lines.

                              A wagon & Pumper with a single 4" line can not move water as well as dual 3.5"
                              A Wagon & Pumper with a single 5" line can move water slightly better than dual 3.5"

                              The risk is that sometimes when you need dual lines, you've only laid a single line. Hopefully this would only happen to the first due unit, who, in an urban area, is going to be less than 300' away from a hydrant. A pumped single 3.5" line will get well over 1000 gpm to the first engine.

                              Conversely, 3" in the street is better than 5" in the bed. While I know some departments are very disciplined about it, it seems many 5" departments allow their engines to respond without laying a line on investigations, or even if nothing is evident on a reported fire. The 3" departments that I'm familiar with never (rarely) respond to any fire-related emergency without laying a line. Furthermore, 3" and I'm assuming 3.5" can be hand-jacked fairly easily to a hydrant within 200'.

                              Comment


                              • #30
                                Originally posted by LaFireEducator
                                RF ...

                                Your scenerio is another excellent use for a 4-Way Valve. The engine starting the lay (either forward or reverse, depending on the situation) simply leaves thier 4-Way Valve at the point thier bed is empty, or in the case of a lay up a driveway, at the point they start the lay at the road. The next truck in simply lays from the first engine's 4-Way valve, until his bed is empty, then he leaves his 4-Way at the end of his lay. If a third bed was needed, the 3rd pump would simply start his lay at the 2nd engine's 4-Way ..... etc. etc.
                                While I do believe the 4-way valve works (and use them), this is the problem: You still have laid out your full load, so you are limited by the friction loss and the max. psi of the hose. If you carry 1500' of 4"LDH and the valve isn;t left in the middle somewhere, you'll not get 1000 gpm to the end. So the 4 way valve only works where it is placed in the lay to allow for the expected gpm. Again, theoretically around 700-800 ft. for 1000 gpm. For this reason our 4" LDH loads have a off color length at 700' to denote the distance we can safely flow 1000 gom. If you are laying for a large defensive operation we break a pumper in at this length of hose. (we have a mix of red and yellow LDH, red bed gets a yellow length and yellow bed gets red)

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