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Member

Join Date: Aug 2009
Location: I am located in India
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Threading for a Fire Hydrant Inlet Connection

11/10/2009 8:02 AM

Dear Colleagues,

This question is regarding the fire hydrant connections.

In India, like in many Asian countries, for plugging in the fire hose into the landing valve (or also called hydrant) we use instantaneous couplings. The hoses are of 63 mm ( 2 1/2") size.

However for a particular project, we have a 4" fire brigade inlet connection for which client would prefer a threaded coupling.

The threads cannot be the standard NPT or BSP as the installation and removal time for the fire hoses will take more of the precious time.

In this case, which sort of threading is best to be adopted.

Thanks

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#1

Re: GM

11/10/2009 8:25 AM

This will depend upon the standards in your district. Check with the municipal authorities on the required standard. Since the Fire Department uses standard equipment, you can't just install any type of fitting you want: it has to comply with certain required standards so that the firemen can rig up their equipment with minimal hassle.

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#2
In reply to #1

Re: GM

11/11/2009 8:11 AM

Better be careful here as not all hydrant nozzle threads are created equally! Some are right-hand "on" while some may be left-hand "on", and then not all threads are equal too, as the coarseness and pitch may differ from one hydrant to the next.

Do as the previous poster in the blog has suggested, and DO check with the municipality that owns the fire hydrant before you attach anything to their nozzles, otherwise you may literally screw-it-up royally by cross-threading etc, and hence, you may have to buy a new hydrant to replace the one you ruined!

Have a great sunny day!

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Guru

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#3

Re: Threading for a Fire Hydrant Inlet Connection

11/11/2009 12:04 PM

You might consider the United States NFPA fire hose coupling thread system. (also called NH thread). A nominal 4 inch thread is 4 threads / inch pitch. For a nominal 2-1/2 hose, the pitch is 7.5 threads / inch. Couplings and adapters are readily available in the US as this is the Fire service standard here

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#4

Re: Threading for a Fire Hydrant Inlet Connection

11/11/2009 12:10 PM

In the United States NPT threading is not used on Fire Hydrants. Instead there is a specification published by the National Fire Protection Association (NFPA) for threading. The threading is designated as NH threading. You did not state the nominal diameter of of the large opening in your the fire hydrants you specify. The number of threads per inch is consistently 4 for the large opening (4 inch nominal size to 6 inch nominal size). Also, the pitch and the thread height are the same. However, the thread designation does change due to diameters. The length of the nipple does vary slightly. For instance, the thread designation for a 5 inch diameter (outside diameter) is 4-4 NH. The first 4 designates the nominal size of the waterway coupling. The second 4 designates the number of threads per inch. NH designates a fire hose coupling.

If interested, rather than reproduce the specifications here, I would suggest you visit the NFPA website. Registration is free. You can look at the specifications but you cannot copy or print them. These thread specifications are duplicated in the American Water Works Association (AWWA) standard C502, which is the AWWA standard for Dry-Barrel Fire Hydrants.

I agree that NPT threading is totally inappropriate. NPT threading for a coupling of this size specifies 8 threads per inch. So twice as many rotations are required to couple the hose to the hydrant.

Anyways, I hope this helps.

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Guru

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#5
In reply to #4

Re: Threading for a Fire Hydrant Inlet Connection

11/11/2009 3:01 PM

Thread specifications can also be found in Machinery' Handbook

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