1. #1
    Firehouse.com Guest

    Question 5" or 6" supply line?

    Our department currently uses 4" supply line.
    We are going to upgrade to either 5" or 6" supply line. I would like more information from departments that are using 6" supply line (pro/cons). Any information would be helpful.

  2. #2
    Firehouse.com Guest


    It has been my experience that although 6" hose can definately move more water than 5" I most cases the municipal water system can not support the big stuff. A small increase will probably be noticed but not worth the effort. If I was the boss I would consider outfitting one unit with the 6" to beused for relay pump operations to support the big fire /big water operation

  3. #3
    Firehouse.com Guest


    Back in the 1980's when LDH started seeing a lot of action in upstate NY, I remember some 4", 5" and some 6". I've used mostly 5", some 4". I don't see or here much about 6" although maybe there is some out there. It seems as though there maybe has been at least some trend toward 5" from both the 4" and 6" side. What about appliances, etc. I don't typically see much for 6", all 4 and 5". Is it out there?
    4" to 5" is a big performance advantage in itself, but 6" would be a big jump as well.

    It really doesn't matter much what your water supply is on which hose to go to. At a hydrant you have a certain water supply available. I'm looking at one right in front of me for Evansville, Indiana. This is the water supply available for an industrial plant that I am working on upgrading the fire sprinkler protection.
    The water supply test was taken at the closet hydrant which is on the corner of a 12" main down one street and a 20" down the other. The water flow data from that hydrant is 56 psi static and 51 psi flowing 1640 gpm.This data can be plotted on a water supply graph. This is a very flat water supply curve, not big pressure, but a lot of flow. If I go down to 10 psi, this water supply will flow over 5,000 gpm. So, with no losses in the supply line, you could flow 3 -1500 to 1750 pumpers at 100% capacity with 10 psi remaining on the intake side of each. These pumpers would have to be basically sitting at the hydrant.

    A quick ball park calc on 4" vs. 5" vs. 6". Let's go out 1000 ft. from this hydrant and calc what kind of water supply you have at the end of each supply line available for a pumper.
    4" - Flow at 10 Psi residual = 350 gpm
    5" - Flow at 10 psi residual = 800 gpm
    6" - Flow at 10 psi residual = 1300 gpm

    You can see a pretty big difference in each. This a very strong water supply, but when you choke it with 4" for 1000 ft., there's not a lot left. 5" is big improvement and 6" let's you pump an engine pretty much at capacity.
    Moving from 4 to 5 to 6 will help any water supply. It really depends on your district. If you have a very strong water supply and very short supply lines, the difference from 4 to 5 to 6 will not be a much. But you can see when you have a low pressure situation and long lays, each jump from 4 to 5 or 5 to 6 will make quite a difference. You could also double lay LDH as well.

    If your interested in the issue of big flows and water supply and the impact of small supply lines and distance, read this: About a year ago there was a major fire in Massachusetts where I grew up. Major fire - 11 buildings destroyed. 16 FDs responded, 17 engines, 7 ladders, 150+ FFs. Predominant supply line - 3". Big follow up after the fire, issues about available water, etc. Water dept figured water used on fire - 200,000 gallon/hour. That's 3,300 gpm. 3,300 gpm for 17 engines! That's about 200 gpm per engine. Each of those engines was flowing a single handline! The mains in the city are pretty decent. This is an old industrial city. The water dept said that about 1 million gallon per hour was available. That's 17,000 gpm or 1,000 gpm for each engine. The problem? It's simple - you've got mains that can flow 17,000 gpm and 17 engine that can flow 1,000 gpm and use that 17,000 gpm, but guess what. You just aren't going to get 17,000 gpm through 3" hose to supply these engines. Big water and big fire pumps, but tiny supply lines.

    If you're still looking at 5 vs 6, I would calculate out a number of representative supply line lays and see what you get. Put a few a few up on the Forum and we'll calc them if you want.
    Good Luck.

  4. #4
    Firehouse.com Guest


    ffeng made some really great points.

    The only thing I'd add is that you need to look at the average lay out distance to your target hazards (big fire/water opportunities). We also have an excellent water system in our city, and have very good (short) spacing on our hydrants. The only time we would have to lay out more than a couple hundred feet of our hose would be in isolated residential areas, where our gpm requirements would not be as dramatic. I don't think that we would need the increased performance of six inch vs the five inch we use now.

    We have had good success in using the five inch in supplying master streams.

    Even ten years ago, we dropped double two and a halves on fires.

  5. #5
    Firehouse.com Guest


    One other factor you may want to consider. The size of your hose bed, how long of a unassisted lay you may encounter, and what we be the typical water demand at that distance. You may want to consider using a smaller line so you can carry longer lays if you think there is a possiblity that you will be doing your intial attack unassisted for longer than your booster tank will last. Even a smaller water supply is better than none especially if you assist it with your booster tank. You will want to take a long look at your coverage area, water supply, and aid. You can put quite a bit more 4" on a bed than 5" and more 5" than 6". Big water is usaully good but doesn't do a lot of good when you come up short of the fire.

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