Kirk Allen: Real World Hydraulics

By Kirk Allen

What is “real world”?  Some refer to that term as everything that happens outside the classroom.  Others use it as the excuse to ignore the class room.  I’m sure most have heard it before:  “Going to that class is a waste of time because what happens here in the “real world” is not the same as what happens in the classroom.”

Having engaged in both “real-world” testing and classroom instruction, I am confident the key to fixing many of our challenges in the fire service can be accomplished by questioning what we were told and demanding proof that the information is based on fact, not opinion.

The most basic hydraulics challenges in this country continue to be addressed the same way today as they were 50-100 years ago.  A simple thumbs-up or thumbs-down is used 99 percent of the time, according to my surveys, even though we teach numerous mathematical formulas for accomplishing the movement of desired flows. With that kind of feedback on fireground hydraulics, we must ask ourselves why is our thumb the go-to device instead of applying the mathematical formulas to our desired flows?  Are the formulas that bad?  Will our thumb hold up in court? Is there a better way?

The key in the process is to identify one important element, “desired flow.”   Whatever that number is, we walk people through a simple step-by-step exposure of key problem areas that have proven to kill desired flows without ever getting tangled up in the age-old fight about which nozzle is a better tool.

Our goal on the “real world” fireground is to apply our desired flow to the fire. Do this, and you should win fairly quickly. However, more often than not, we do not get the fire out for a long list of reasons; but we are finding that the biggest reason is that that mysterious desired flow was just that, mysterious.

We teach day in and day about friction loss (FL) for this length of hose, this appliance, this nozzle, and so on;  sadly, more often than not, no one is asking the most important question that impacts each and every aspect of that teaching–for what flow?

You see, it’s all about application rate or gallons per minute (gpm).  Knowing all the FL information in the world does us no good if we don’t know the flow.  As flow goes up, so does FL, yet the very equation we are being taught has no reference to gpm?

DP = FL + NP + (plus or minus for elevation + appliance)


Says who? and With what proof? are two questions we have learned over time that may well be the key to getting facts instead of opinions.  Just because a person is standing in the front of a room teaching does not mean that person is correct. We must challenge our teaching!  Apply the simple “says who” and “with what proof questions to the basic hydraulic issues we all face.

1.       The discharge is open.

2.       The pressure is 100.pounds per square inch (psi).

3.       The FL is XX per 100 feet.

4.       Each section of hose is 50 feet long.

5.       The friction loss in that appliance is 10 psi.

Assume for the sake of discussion that your instructor told you the five statements above. Now, you would have to validate the teaching with the second and most important element in the education process, proof!

·         Is the discharge really open just because you pulled the handle out?

·         Is the pressure gauge really 100 psi just because the needle is on 100?

·         Is the FL really XX in that 100 feet of hose? How do you know?

·         Is the hose really 50 feet?

·         Is the FL really 10 psi for that appliance?

“That fire kicked our tail all night because it was big and hot.”  Or is it possible that the fire referred to as big and hot was simply not getting the flow you “thought” you were providing?  How many after-incident critiques have addressed the simple question of “what” were we flowing at that fire? Determining that answer may well point to the real reason we spent all night at the fire.  We have allowed ourselves to live up to our name fire“fighter” instead of being fire “suppressors.”  I know it sounds corny, but think about what we are really trying to accomplish.

Fire suppression is our goal, and that is accomplished through heat absorption as it relates to our flow rates, yet the vast majority of our teaching has been about pressure, FL, elevation, and so on—none of which absorbs heat!  During measured flow testing, we must not only establish a desired flow rate but also identify problems in the system that make getting that flow rate difficult, if not impossible.

We pull a lever and see water come out the end of the nozzle. We “assume” our discharge valve is open.  Have you ever opened that very valve and looked inside the waterway to see if it is open all the way? (Please don’t do that with the pump engaged. J ) Depending on the materials of the valve and the linkage, wear can prevent the valve from opening all the way, thus restricting the flow.

We read a pressure gauge on the panel and assume it’s accurate.  How often do you check those gauges?  Simply capping the discharges a couple of times a year and opening all of them can tell you if you have a gauge problem.  Bring the Master to 150 psi and look at all the gauges to see if they, too, read the same pressure.  We have found gauges that were off by as much as 30 psi. Without proper testing, no one had any idea that the reading was that inaccurate.  

Fire academies across the country are teaching a test answer of FL per 100 feet of hose, and it’s drilled into students’ heads throughout the course. Is anyone asking, “For what flow” or for which model of hose? About now, some “experts” are going to infer that  only a ballpark figure gets you close.  

Close to the pressure needed?

Fifteen brands of hose required 12 different pressures to get the same flow rate.  Close?  Those pressures ranged from as low as 20 psi per 100 feet up to 64 psi for a flow rate of 180 gpm.  The next time you’re told it gets you in the ballpark, make them prove it with the equipment “you” use!   

We open a box of hose, pressure test it, and now even flow test it, and put it on the engine, and call it good.  We are excited that we finally spent some money and got new hose.  You pay for it by the foot.  When was the last time you pulled out a tape measure and checked to see what the real length was?  We have opened brand new boxes of hose that were to be 50 feet; in reality, they were only 47 feet in length.  Amazingly, we have had chiefs share with us stories of hose lengths that were as short as 38 feet. They were charged for 50 feet.  Measure your hose.

“Ten psi per appliance!”  For what flow rate?  A standard 2½- to 1½-inch reducer can have as much as 40 psi of friction loss, depending on the flow rate.  Measure it!

Negligence is one of the greatest sources of civil litigation.  Can you place your hand on the bible before a judge and jury and tell them with any confidence what your flow rates were the night of the fire where lives were lost?  All too often, we send our brothers and sisters into battle to slay the dragon when, more often than not, we could not say with confidence what gpm they were flowing–let alone flowing what the standards state they should be flowing.

Most know how many miles per gallon they get in their vehicle or understand the importance of balancing their checkbook (yes, some of us still have a checkbook), yet ask them what their flow rate was at the last fire they went to and you will get a deer-in-the-headlights response.

If you have not been through the process of calibrating the equipment and measuring your flow rates so that you “know” what it takes to get the flow you want, take a class in real world hydraulics.


Kirk Allen has served eight years as the Kansas (IL) Fire Protection District chief and is an active EMT. Having spent a career in the U.S. Air Force, he acquired a background in aircraft propulsion, is an FAA-licensed air frame and power plant technician, and gained extensive knowledge in aircraft crash rescue. He has served 23-plus years in and with volunteer and career fire departments in the areas of hazmat and fireground hydraulics. He has been a hydraulics instructor for the past 23 years.

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