I enjoy reading textbooks and articles on hydraulics and what formulas to use when flowing water to extinguish the fire properly.  These are great foundations in the fire service but not 100% true. 


After attending an FDIC class on "Real World Hydraulics" by a Chief Kirk Allen, this open my eyes and my mind to water flows.  Not all pumps are created the same nor are all hoses created the same. 


Pumps, depending on how you spec it for your apparatus, could have as many as four elbows and cause friction loss at 5 psi per a bend or more.  So you could lose considerable amount of pressure before the water has left the pump and been introduced into your hoseline(s).


Not all hose lines are exactly 50 or 100 ft.  He showed us hoses that were suppose to be 50 ft, but were as much as three or four feet short.  This can be critical in a 200' pre-connect that could end about 20 feet short.  Also, the internal lining can have a factor on water flow and increase or decrease friction loss. 


Bottom line, you're better off metering your own hoselines and label each gate/valve to let you know that if you want 50 psi (smoothbore) or 100 psi (automatic/fog) at the nozzle tip then these are the pressures you need for either one. 


It does cover you legally in the court system when the lawyers (legal eagles) doubt that you gave enough pressure for those hoselines to save that family member who got burned and accuse you of giving more pressure for your own family.  Always think liability nowadays :)


True story, did flow metering on the first-due engine at work and found on the of speedlays to have four elbows in the pump and we could only achieve 90 psi at the tip of a automatic nozzle through 200 feet of two-inch hose while operating at 200 psi.  Looks like we'll be giving that line a smoothbore nozzle soon.



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