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For years nearly every nozzle manufacture has been attempting to bring some type of new and attractive technology to the tried and true smooth bore. In my short career I have seen countless variations of integrated, variable choice, or adjustable diameter tips/nozzles, none of which have gained much traction beyond the exhibition floor.

Some would stop the conversation right here and say that these failed attempts are proof we should just leave well enough alone. They may claim that the simplicity of the smooth bore is its most desirable attribute, and if it hasn't changed in the hundreds of years of service it should not be changed now.

I agree with these sentiments however, I believe we have seen advancement in smooth bore nozzles and another move forward has just occurred. The reason the masses aren't "seeing" changes in smooth bore nozzles is because the changes are occurring at an evolutionary pace and are physically very subtle but they are occurring. For this piece I will stick with the 2 1/2" attack line and smooth bore nozzles to best demonstrate this steady progression and the most recent step.

The original, and still to this day most common 2 1/2" smooth bore nozzle is known as the "hydrant" or "ISO" stack. Typically found on the traditional playpipe shut off, these nozzles have been virtually unchanged for over a hundred years. The source of this nozzle was a time where the 2 1/2" hose was the "99% of the time" line for attack, master stream and supply, also most firefighting was done from the exterior or just inside. The reason for the 2 1/2" and this design was that pressure was the greatest challenge of the time for the fire service both in consistence and amount. The 2 1/2" line provided a low friction loss line that was still maneuverable especially when it was pulled around by two firefighters using the handles on the playpipe. The series of tips allowed firefighters to adjust to the various pressures and maintain a good stream; consider it a manual automatic nozzle.

Over time firefighting operations have certainly changed. The reliability and ability of fire apparatus and infrastructure to provide consistent and quality pressure for firefighting operations has improved 10 fold from the turn of the last century. With SCBA, firefighting operations moved interior and with that the push for 1 1/2" and 1 3/4" hose has given operators more choices. With that tide of transition came a clear adaptation of the smooth bore to the more modern time.

With the prevalence of the 1 3/4" lines flowing between 150 and 185 GPM it seemed unnecessary to maintain a 1" tip on the much larger 2 1/2" line that only provided between 25 and 60 more GPM. With that many departments pushed for the hydrant stack of three tips to be reduced to two. The two remaining tips (1 1/8" and 1 1/4") remained stacked not to ensure a quality stream through pressure fluctuation, but to provide options in attack power. The 1 1/8" tip could be the "go to" for most 2 1/2" operations by providing 265 GPM and if the training/comfort level of the crew or the amount of fire upon arrival dictates a simple tip removal increases your fire power by almost 25% going up to the 1 1/4" at 328 GPM.

The "Indy Stack", as it is now known, is also now commonly found on standard 2 1/2" nozzle shut offs. The size and weight of the playpipe hinders most active and interior firefighting operations. Many of the original design features of the playpipe were for defensive operations and are just not a part of modern day technique. The greatest example of this is the portable master stream. In the "old days" you would see pictures of defensive firegrounds that would be seas of 2 1/2" lines and operators. The reason being is the 2 1/2" was both their attack lines (1" and 1 1/8") and their master streams (1 1/4"). Today's defensive fire  grounds are primarily portable and or unmanned master streams (1 3/8" +). These modern master streams are well beyond the flow range of the 2 1/2". Most of these devices are fed by a minimum of 3", two 2 1/2"s or even 5" in some cases. If your department is still consistently equipping your apparatus with these playpipe shut offs you should make sure that there is reasoning behind it to meet a standard, to match training and operations or is it "just because".

Now to discuss the latest advancement of the smooth bore and that is the new bore. In the last year a few nozzle manufactures have tooled up to produce an 1 3/16" tip. The creation of the 1 3/16" tip has been largely driven by the work of Oakland (CA) Fire Department Captain (Ret.) Dennis LeGear. Captain LeGear refers to the 1 3/16" as the "missing" tip because of its absence as an option until recently.

We often get fixated on a 50 PSI operating pressure for smooth bore nozzles. While 50 PSI creates the optimal stream quality, the smooth bore is like all nozzles and has a functional range between 40 and 60 PSI. As you can see above the functional range of the single 1 3/16" tip covers the GPM flows of the 1 1/8" and 1 1/4" while also providing an optimal stream at an intermediate 296 GPM. The beauty of the 296 GPM at 50 PSI target is that NFPA recommendation and industry common practice for 1 3/4" attack lines is 150 GPM or better for interior fire attack. When you set up your engine companies with a 2 1/2" and 1 3/16" tip you are not only "going with the big line" you are doubling your attack volume with that bigger line. The single tip simplifies hydraulic calculations, communications and variables of two tips. The single tip on a shut off also reduces the total length and weight of the nozzle package resulting in better balance and reduction of nozzle whip when operating.

Another factor in today's 2 1/2" nozzle selection is the pairing with modern hose. Once again the work of Captain LeGear has made many of us as operators that the internal diameter of our hose has increased over the years. As much as we would like to trust that hose manufactures are reducing friction loss and weight through technological advances in materials, it just isn't the case. The greatest factor in decreasing friction loss and increasing flow is the internal diameter of the hose. As the internal diameter expands friction loss is reduced and more water can be moved through the line.

If pump charts are not adjusted to the specific friction loss characteristics of the hose hose in service and coefficients associated with a true 2 ½” internal diameter are used, the line will be over pumped.  This piece of modern hose construction creates even greater support for moving towards an 1 3/16" tip as an attack package.

Below is an example of  the 1 3/16” tip when you apply current 2 11/16” friction loss coefficient as compared to the 1 1/8” tip with the traditional 2 1/2" based coefficient.

  • Friction loss per 100’ of 2 ½” hose flowing 265 GPM from a 1 1/8” smooth bore tip using the 2 1/2" coefficient of 2 is 14 psi
  • Friction loss per 100’ of 2 ½” hose flowing 296 GPM from a 1 3/16” smooth bore tip using a modern 2 11/16" hose internal diameter coefficient of 1.4 is 12 psi

Technically if you are using IFSTA based coefficients and modern 2 ½” hose you could just go replace all the 1 1/8” tips on your attack lines with a 1 3/16” and you would be flowing over 300 GPM or 5 gallons per second from your lines without anyone even knowing.

The release of a "new" smooth bore will not get many people in the fire service excited, some may not even recognize it and most will possibly never even hear about it. The biggest factor in this is because the smooth bore is not an item that needs replacement. These tips can and do see a hundred years of service without issue but that lack of attention may be resulting in a lack of opportunity for you and your department in operational potential and efficiency.

I would not expect anyone to just up and replace their hydrant stacks or Indy stacks today in favor of the 1 3/16" tip because you and I both know they work just fine. I do believe that there is value in evaluating it as an option for future purchases. Next time a nozzle vendor makes themselves available, or you start to spec out a new apparatus, discuss these smooth bore advancements and find out where your equipment and operations are and where you would like to be.

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Comment by Jim Derrick on June 11, 2015 at 5:07pm

Great article as always Brian, Thank you for the info

Comment by Chad Menard on May 24, 2015 at 8:51am

Awesome article with plenty of math to back up the talk! Always great work! Keep it up!

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