Mike: The imperical formula developed in the 1880's called the Hazen-Williams formulae for pipe puts the pipe diameter raised to the 4.87 power in the bottom of the equation. Try taking your friction loss number and multiplying it by your nominal hose diameter raised to the 5th power. We will use a typical US hose size of 5" with a Fl of 6 psi/100 at 1,000 gpm. 5^5=3125 so the number becomes 6 * 3125 = 18,750. Lets assume that new hose diameter expands by 1/4" under pressure so 5.25 raised to the 5th power is 3988 and the friction loss drops from 6 psi per hundred to 4.7 psi per hundred ft. Newer hose weaves, particularly single jacket or urethane covered can easily grow by 1/2 inch in diameter.
"We placed an inline pressure gauge at various positions along hose lines of various configurations and flow rates."
Did you compare static pressure on that gauge with the panel gauge to make sure it was reading accurate? Did you use a calibrated flow meter to establish the flow rate for the test? If not, the reduced FL number may be becuase your not flowing the flow you think.
Are you testing off the side discharge? If so, realize those numbers are going to be quite different in most cases because of the difference in plumbing from crosslays, preconnets, etc.
The best research I have been able to confirm is that the co-efficiants were based on testing with in line gauges at each connection and measuring the actual pressure drop in each section of hose based on a measured flow. The reason for doing this was it established a known set of numbers for a specific peice of hose. That element has been lost in todays marketing and education system. We flow test and FL test each section of hose once each year. When I see a climb in FL from year to year then I know I have something going on inside that section of hose.
Different hose will have different numbers. I have seen first hand one brand hose that could flow 80gpm more than another. The best we could tell was the high FL hose had a much rougher liner than the other. Bothed measured 1.80" ID.
"I know this may seem fairly insignificant, but if we are to emphasise the importance of hydraulic knowledge and provide information to our firefighters, I think we need to reflect reality and be accurate."
God Bless You! It is NOT insignificant! Our lives are on the line! I have begged Fire Schools, Universities, Big city departments etc for years to change what they are teaching becasue all they are doing is teaching a guy how to pass a test.
I prove weekly that the information in the text book more often than not is wrong. I cant tell you how many times people come up with numbers and then want to put it in an SOP only to find out the numbers are not going to work on each engine, let alone each pre-connect.
We need to teach a FLOW based hydraulics that is established using calibrated flow meters. Flow Meters that YOU can calibrate in the field, not one that some manufacture tells you is good to go for a year.
Test everything in the manner which you are going to use it. I know pulling a crosslay or preconnect gets the guys upset because they have to put it back but those numbers are what you need.
Flow meter on the intake side. Tank to Pump Closed, Tank Fill Closed, Recirculation line closed:
Put a pressure gauge in the preconnect at the hose inlet. Place another one at the Nozzle inlet. Charge the line and see if the panel gauges and the inline gauges are reading the same. If they are, flow water to a smooth bore of a known size (15/16ths @50psi = 185gpm) and pito the stream (NFPA14 explains how) and make sure the flow meter is in fact reading what it is suppose to for the pressure on the smooth bore.
Once thats done, test away! If your pumping 150psi and your hose inlet gauge shows 100, then you have already lost 50 psi in the plumbing before it even gets to the hose.
We build pump charts specific to the equipment on each engine. Flow based numbers not Pressure based. Sure, we pump a given pressure but we have to focus on the flow, not the pressure.
If using an automatic governor I prefer to use it in RPM mode instead of Pressure mode. There tends to be far less idling down when the hose is kinked in RPM mode than in pressure mode. I have seen governors idle the endine down for a hose kink that only makes the flow problem worse. If I had it my way I would have manual throttles on every engine!
Its exciting to see more folks realizing the book numbers are not accurate. I urge everyone to start asking two questions when people make a claim or a text book states something:
Says Who? and With What Proof?
"Our outlet gauges are at the coupling on the pump, so are on the discharge side of the pump plumbing"
I suspect the pressure sensors were installed just downstream of the discharge valve which only tells you the pressure at that point. Its the plumbing from the sensor location to the actual hose connection that is not being accounted for and unless your engine specification outlined where to put the sensor I suspect you will find its not anywhere near the hose connection, accept for the side discharges, which has them right after the valve which is right behind the panel.
"I'm currently talking to a hose supplier to try and get some facts around this. "
I have to say I get a chuckle out of that comment and I have to say, Good Luck and please let me know what they tell you!.
Chief Halton and I several years ago did a right up in Firehouse on this topic and after contacting 13 hose manufactures there was only ONE that had any fact based measured numbers and those numbers were the very ones I provided for them as they ALL had no clue! They just kept pointing to NFPA formulas. It was a sad thing to see and unfortunatly its pretty much the same with the exception of a couple manufactures.