1. #1
    Forum Member

    Join Date
    Oct 2010
    Very Rural Kansas

    Default Question about Hydrants??

    My Department just recently color coded our fire hydrants to NFPA standards,

    Red top = less than 500 gpm
    Orange top = 501-1000 gpm
    Green top = 1001-1500
    Blue top = 1501 on up

    My questions is how do I figure out a rough guestimate of how many gallons per minute are actually flowing into the truck from the supply line?

    My department uses a forward lay using one 2.5 inch supply line. Yes.....we still use 2.5 inch supply line......right now we are having a argument because some of our older fireman believe that it doesn't do any good to hook more than one 2.5 inch supply line from the same hydrant to the same truck.....but thats another story......

    If you lay 200 foot of 2.5 inch supply line from a hydrant to the truck on a red hydrant (max 500 gpm), how may gallons per minute are actually reaching the truck?

    Same question for a Orange top hydrant?

    Same questions for a Green top Hydrant?

    Same question for a Blue top Hydrant?

    Is there a easy formula you can do in your head? I'm just looking for a quick estimate???

    One of the things we did find doing this is that the majority of Hydrants in town were red tops with a great number of them only flowing about 150gpm.....thats a huge problem that the City staff had been hiding from us over the years.......
    Thanks in Advacne for your help......

  2. #2
    MembersZone Subscriber

    Join Date
    Jan 2007
    Pa Wilds


    iggerz: Take a look at this thread to see if it helps answer your question. If not repost here and I'll try to help. http://www.firehouse.com/forums/show...=pressure+drop (Static Pressure vs Avail Flow)


  3. #3
    MembersZone Subscriber

    Join Date
    Jan 2007
    Pa Wilds


    Continuing on with your question... Get the static & residual pressures that your City Staff recorded when they tested the hydrants. Find a copy of a "Hydrant Analysis Graph" that you can use to analyze the available flow. This is a very simple graph that will provide a pressure for every flow coming from a hydrant by drawing a line through the "Static" pressure and the residual pressure and flow measured by your City Staff. The difficult part of your question is that we do not know the length of 2 1/2" line supplying your engine. I am sure you are aware of the estimated friction loss in the line. (2Q squared + Q) or some other method of estimating. Suppose we wanted to supply two preconnect hand lines at 150 gpm each. Total 300 gpm or a loss of about 13 psi per hundred feet. A very respectable hydrant might supply 60 psi static and 300 gpm at 54 psi residual. With a 400 ft. forward lay we will have (13 x 4) 52 psi friction loss to supply the 300 gpm and the compound on the engine would be almost zero (2 psi). While the hydrant could supply at least 900 gpm if you hooked direct, by making a forward lay of 2 1/2" you will never get any more than the original 300 gpm. A poor use of the available hydrant supply. Changing to a 5" supply line would provide the same 300 gpm with an incoming compound reading at the engine (3x3/15 * 4= 2.4) of 51.6 psi. Obviously there would be a lot more water available. Since the estimator says that a 15% or less drop should supply an additional two lines, you could expect a total of about 900 gpm. If graphing your hydrants does anything, it should cause a lot of rethinking about using 2 1/2" line as supply.

  4. #4
    Forum Member
    Bones42's Avatar
    Join Date
    Mar 2001
    Pt. Beach, NJ


    Remember, regardless of the hydrant...no more water is flowing in than what you are putting out.
    "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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