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WEEKLY TAKEAWAYS AS A FIRE PROTECTION ENGINEER

Breaking Down Components of a Fire Hydrant

7/24/2018

 
Aside from being the historically-preferred location for canine  bladder relief, fire hydrants serve an important function in providing access to a water supply system.​​
Fire Hydrant
Types
Fire Hydrants fall within one of two types; wet and dry barrel.

Dry Barrel, as implied, is not water-filled until the hydrant valve is opened. Dry hydrants are overwhelmingly the most popular type of hydrant within the United States to provide insulate using depth to prevent freezing portions of the water supply.

Wet Barrel hydrants, though infrequent, are used in portions of southern California and Florida. These hydrants have one or more operating stems which run horizontal at each outlet. As implied, wet barrel hydrants are water-filled at all times.
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Bonnet
The conical cap for the hydrant, or bonnet, holds the operating stem nut in place and protects the hydrant from mechanical damage and water penetration.

Branch
The branch pipe serving the hydrant from the city main is one restriction for the overall capacity of a hydrant. While older systems often connect hydrants with 4-inch branch pipe, a minimum of 6-inch pipe should be used to limit pressure loss and permit greater flow capacity. Our friction loss tool can be helpful in estimating loss through these pipes.

Flange
The flange at the base of the hydrant is the point of connection for the hydrant to the rest of the barrel. 

While the dimension from the bonnet to the flange of the hydrant is standard, the height of the flange becomes important during installation as it determines the height of the outlets. Because hydrants need to be quickly accessed during an active fire, hydrant outlets need to be installed tall enough to allow a full-revolution of a hydrant wrench from the lowest outlet.

Hydrant Color
Some jurisdictions paint hydrants or hydrant bonnets to identify the capacity of the hydrant.

NFPA 291, the Recommended Practice for Fire Flow Testing and Marking of Hydrants, suggests hydrant colors as Red/Class C, Orange/Class B, Green/Class A, and Light Blue/Class AA for Less than 500 gpm, up to 1,000 gpm, up to 1,500 gpm, and 1,500 gpm and more, respectively (NFPA 291-2019 5.2.1.2). 

Outlets
A traditional dry barrel fire hydrant contains three outlets: two 2 1/2-inch (65 mm) side outlets and a single 4 1/2-inch (115 mm) or 6-inch (150 mm) "pumper" outlet. The latter outlet gets its name as it is often the preferred choice for the fire department to connect and feed pumper trucks.

The size and number of the outlets serve as one limit to the capacity of the hydrant. While the typical hydrant described above is the most common type, other combinations certainly exist - downtown St. Louis, for instance, have hydrants with only a single pumper outlet. 

​Stem Nut
The stem nut is the key to operating the valve within the hydrant. Typically shaped as a pentagon, the stem nut will turn the operating stem of the hydrant and raise the valve to an 'open' position when turned with a hydrant wrench.

Thrust Block
Unless mechanically restrained, thrust blocks serve as a way to distribute the hydraulic force of the pipe network into the soil. Our thrust block calculator can be helpful in sizing these blocks.

Valve
When in the 'open' position, the valve at the bottom of a dry barrel hydrant rises to plug drain holes and simultaneously permit water to fill the barrel of the hydrant.

When in the 'closed' position, the valve lowers to block water passage and re-open drain holes at the bottom of the hydrant. These drain holes act as weeps which slowly drain the hydrant barrel and help prevent freezing.

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Michele Rivarola
7/25/2018 11:04:16 am

Thrust block missing at the tee

JOE
7/25/2018 11:36:39 am

Thanks! I knew I should have drawn it in. Will update just to avoid confusion if nothing else.

Zach Raley
8/11/2018 08:41:49 am

Hey Joseph,

I’m a former Utility Director that now has a Utility Service Asset Management Company and Fire Consulting and Service Company. I really like the drawings, information and way you have laid things out. I’ve been redesigning my website and looking to draw out or get pictures like you have drawn.

Would you be willing to send me the drawings if I put a reference to you on the pictures to use in our website? I agree with comment that a thrust block on the tee would be a good adder.

We perform comprehensive fire hydrant services and valve services to both Utility and Fire Departments. I consider us a good bridge between two different departments the have common ground in assets.

We follow all AWWA and NFPA Standards. We operate in Louisiana, Arkansas, Texas, Oklahoma and Colorado.

Look forward to some conversations.

Thanks,
Zach

Joe Meyer
8/13/2018 08:15:32 am

Thanks Zach! Email me at jdmeyer@meyerfire.com and let's talk about it in more detail. Thanks!

Tiffany Locke link
9/11/2018 11:02:08 pm

Thanks for explaining how there are both wet and dry barrel fire hydrants, which has to do with when it's filled and the dry ones or more popular to provide insulate using depth to prevent freezing. I'd imagine that it would be important for people to understand the difference, in order to make sure that they're used properly when necessary. Knowing would probably help for choosing the right accessories as well, such as fire hydrant adapters.

Angela Waterford link
9/3/2019 03:40:43 pm

Wow, I didn't know that fire hydrants have wet barrel and dry barrel categories, and I might ask an expert which one should be installed near my building. I think that I should ask for their opinion first because this will make sure that my apartment is up to code. In addition to that, it will make sure that in case a fire breaks out, the firefighters will be able to have access to water immediately.

sushma link
2/10/2020 06:09:04 am

Hi,
Great Article! Thanks for providing good services. Great explanation of the fire hydrants. People always want to learn something by reading post Keep learning and keep sharing. Anyways, that's amazing Keep up the great work. All the best.

Jared Danton
5/19/2020 06:41:59 pm

Very good information.


Comments are closed.
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The views, opinions, and information found on this site represent solely the author shown and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a commission for orders placed elsewhere.
  • Blog
  • Daily
  • Exam Prep
    • CFPS Tools
    • NICET Tools
    • PE Forum & Errata
    • PE Problems
    • PE Store
    • PE Tools
    • PE Prep Series
  • TOOLS
    • TOOLKIT (FREE TRIAL)
    • *TOOLKIT (PURCHASE)
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND
    • FIRE PUMP ANALYZER
    • FIRE PUMP DATABASE*
    • FIRE FLOW CALCULATOR*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'19)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • REMOTE AREA ANALYZER
    • QUICK RESPONSE AREA REDUCTION
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • CODE CALLS
  • LOGIN
  • STORE
  • About