I recently came in contact with a department that was looking to change from 5" LDH to 4" LDH, I Know that I work for a department that made the change in the opposite direction, saying that the one inch differece, was big to the extent of close to double the friction loss when moving big water. I would like to hear any other feed back from you all, so that when I debate with this desk commander, I can present a good case. I think they main objective is the weight and size of the hose when it is charged, which is in my opinion, most of the time when your needing a supply line its because you have a big enough fire that you need water, why not have alot of water.

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Current dept has 5" and my former dept used 4", really, there is not much difference. Friction loss really is not a big issue between the two. Moving a charged LDH, be it 4" or 5" isn't really easy either way.


The questions that should be asked is if you run MA, what are other depts using, and would it pay to get adapters to work between the different sizes? Also what is the condition of the current hose? Does it make sense to buy a ton of new hose for something as trivial as moving a charged LDH or minimal friction loss difference? I would bet money could be better used elsewhere. 

Theres where it doesnt make sense John, everyone surrounding them is 5". And friction loss is alot more then you think. When you look at the charts in some cases. For discussion sake, we will take flows in which supply lines are very important: 1000gpm- 4" 6.5  5" 2 per 100'  1500 gpm 4"-13 and 5"-5 per 100'  and then 2000gpm 4"- 26  5" - 10 per 100'. Most of the ladders and platforms in our area are rated to flow 1500 or greater. When you start talking about 800-900' lays that are common, 1500 gpm that is 104 just in friction loss, then add whatever the evolution that is being played out, it takes it toll. with the same senario you are talking 40  with 5".
We still use 3" supply hose in the DCFD.

If you are using LDH, go with 5" for the additional volume with the same amount of effort.


Friction loss difference from 4" to 5" is negligible, even for a 1,000 foot lay.

Moving the line when charged - not a good idea.  We train our firefighters to put the line where they want it and to remove any kinks before the line is charged, so moving it isn't difficult.


Picking it up - just break all the couplings and drain the hose before reloading it.

We routinely pick up 400 to 1,000 feet of 5-inch with 3-firefighter crews.  We also have a tool called the "Roll-N-Rack" that helps pick up the line and roll it.  That greatly helps when we pick up the line.

Mark, 5" is the way to go. You have the additional volume. Its a mess to put down but when you need volume of water flow you have it. Pickup can be bad in real cold weather. But Three Firefighters can get the truck packed back. I have always found that cleanup is always harder than putting out the fire. TV makes it look so easy!

My department runs 4" LDH and it does just fine. A couple departments around us use 5" and the true difference is after a fire when you have to put it back on the engine.  There is a big weight difference.


 99% of the time we use 3" supply. Most times we lay a single line ,on  bigger fires we lay dual 3" lines. We have 5" however it rarely gets laid. 

Depending on the fire load we'er using a double lay of 2.5" and 3". Larger fire loads or supply to tower ladders, 5".

The friction loss difference in a short lay isn't such a big issue.  The reall difference shows in both higher flows and longer distances.


The truth is though, you can flow 1000 gpm through multiple 2 1/2's, multiple 3's, single 4, or single 5 inch lines.  Frankly, I would rather lay out a single 5 inch line and then pick up a single 5 inch line than lay out from multiple 2 1/2 lines from multiple engines to supply that same 1000 gpm, and likely have to pump them to make it work. 


Maybe one of you that does the choice of laying multiple smaller lines for a "small" fire and LDH for a "larger" fire can explain that to me.  I guess it seems like far moe work than it needs to be.  Lay one aldh line, get all the water the hydrant can give you if you need it, when you are done lick up and reload one line.  Seems like a no braine to me.

Well, I guess what I was surprised about, is if your trucks are "all equipt with 5" why change? I heard one of the complaints was it was too heavy? and in florida we really dont have to worry about cold weather. Man up,,,, Big fires require real firefighters to show up to go out. This is the job, even on the volunteer level, it is what it is... What is it all coming to? Our we really making the right moves out there to compensate for the few?
From experience we acutually made the mistake of going form 5" to 4". We had several issuse with long distance hose lays. Laying line beyong 500 ft may require relay operations. This requires additional training and possibly SOP updates. Secondly, supplying aerial apparatus can be challenging with 4' inch line. In our case our engines supply our aerial master streams, this means we were using a 4' supply line and discharging the same size line into the intake of the aerial. Max GPM was between 850 GPM at 265 psi. We went back to 300psi 5" LDH. We still have trouble spots in the city but most have been significantly reduced by going back to 5" LDH. When you add all the hydraulics and claculations, it just make sense to stay or go with 5" LDH.

Yeah I tried this route, showing them calculations when dealing with supply aerial apparatus, but they keep coming up with the weight issue. The friction loss is a no brainer when it comes to the difference here. The time when you need a good supply line, you need the most amount of water with the least amount of friction loss. We all know the statistics that most fires are truley handled with one line and less then a tank of water. Supply lines are for those fires that don't follow the rules and statistics. Hell, the only issue my department has lately with our 5" and this could go for any size, is the damm locks on the storz coupling. My driver sometimes has a hell of time getting the coupling to break by himself.

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