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.
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.
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.
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.
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.
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.