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Hello guys.


My department just entered the 1980's and are starting to use our first smooth bore nozzles. We are going to have a 15/16 tip on our 200' 1.75" crosslay and our 2.5" crosslay will have an 1 1/4 tip on it.


I am looking for info for cheat sheets on calculations to put on my engine for easy viewing of pump discharge pressures, friction loss and flow rates for both size tips. Any help will be great.


Thanks all and be safe.

Joe McClelland

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Replies to This Discussion


Hi Joe:


  You can make your own up using the Freeman's formula to figure out flow (GPM = 29.7 x diameter squared x square root of pressure) and then q formulas for the friction loss.  (12Q squared for the 1.75" and 2Q squared for the 2.5".)  Using this method will get you about 180ish gpm for the flow on the 15/16 and a desired EP of 145ish psi for the 1.75" line.  A 1.25" tip flows 325 gpm at 50 psi and most people pump it at 85 psi EP for 200' of 2.5" line.  


  However since hose and appliances vary from the text book in their friction loss you would probably be better served by testing to establish your own discharge pressure(s).  I would get a pitot gauge and test each nozzle at a nozzle pressure of 50, 60 & 70 psi.  Write this down in a table format and you will know exactly what you have to pump that discharge at to get your desired flow rate.  Some companies mark this on the gauge itself with a paint pen.  


 Hope this helps and best of luck.


Alan Butsch


Thanks Alan.



I would agree with flow testing your own to get "true" flow figures. One other thing I would check would be from the manufacturer of the nozzle what nozzle pressure they recommend.


For example: We use a combination smoothbore nozzle with fog tip attachment. The fog is a 75 psi tip, and we have had discussions on what the nozzle pressure is recommended for that nozzle when used as a smoothbore (which we remove the tip fairly regularly.) When we do our actual flow testing it may clear some confusion.

When I calculate the Friction Loss I can only find coefficient = 15 for 1.75" line.  Where are you getting c=12?  Using c=15 gives a PDP of about 175 which is way too much pressure in my opinion.  When flowing our smooth bore (which is a breakaway TFT 15/16") the stream does not look better at pressures higher than 130psi.  I have also seen c=10 used for this.  The only reason I ask is to have a coefficient reference so when I ask to update our pump charts I have a resource to back up my recommendations. 




  We use 12 in Maryland; comes from our state training institute MFRI.  I believe 15 predates modern hose construction which is smoother and thus creates less friction loss.  If you want to get real finicky, check the hose manufacturer's website and they will give you their figures; however I would still flow test them.  We have Ponn and I have not found their tables to be entirely accurate.  


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