| A Fairy Tale Around Every Corner — By Larry H. Stevens |
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Editor’s note: Everyone has an opinion about nozzles. But every aspect--except likes and dislikes--can be quantified and measured. This three-part series of articles will draw some fire. So fire away with your ideas and opinions, and make the pages of Fire-Rescue News! Here we are in the eighth generation of nozzles, or is it the ninth? The first generation was smooth bores; the second, smooth bores with shut offs; the third, twist-type variable and fixed-flow combination fog nozzles; the fourth, fixed-flow combination fog nozzles with shut offs; the fifth, fog-and-smooth bore combination nozzles. The sixth generation was a combination fog nozzle with two- or three-flow settings; the seventh, combination fog nozzles with flow control rings; and the eighth, variable-flow constant-pressure automatic combination fog nozzles with and without flow control rings and shut offs. I was a little perplexed to read about the new nozzle technology that does everything an automatic does and much more. It’s called a fixed-flow nozzle. I thought that was a 1950s fourth-generation nozzle. I was once told that if you don’t learn from the past, you cannot help but repeat its mistakes. The new nozzle purports to give quality stream performance at 50 psi. It also gives control of flow to the pump operator. It is so simple even the dummy at the nozzle will get a stream if he can figure out how to open it, and it supposedly meets NFPA standards. |
| In Search of the Holy Grail |
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What is the ideal nozzle? It’s the one that will put out the
fire. Right? Wrong! It is the one that will work on a majority of
your fires. Every make and style of nozzle is fighting fire
someplace. Even old Navy combination fog-straight stream nozzles
with 6’ applicators are coming back in some areas on brand
new apparatus. Everyone is looking for something new in a nozzle.
That is why I am so perplexed at this so called new revolutionary
nozzle technology. The fixed-flow combination nozzle with a shut off isn’t new; it is the same stuff my grandfather--and probably yours, too--ran out of the department 40 years ago because it was unworkable. Twenty years before that it began replacing what everyone used: the smooth bore tip. In those days, the only choices were the simple booster or a 2 1/2" hose. Rich departments attached gate valves of various designs to their smooth bores to give some control. Some of the valves required spinning a crank as much as 20 times to shut the line off. The departments that didn’t have the money for gates basically operated like the old images we see in paintings--without a shut off. When another line was shut off or if a pressure surge occurred, the nozzleman went flying. There are some firefighters in every department who remember having a complete range of smooth bore tips 3/4, 1, 1 1/8 and 1 1/4" in diameter. Progressive departments, like Salt Lake City, used a 1 1/2" tip for even higher flows. Which size tip did they store on the line? The small one! Why? Because the water supply conditions varied so much it was the only sure thing you could supply off tank water or off the water system. It was thought you could always shut down and change to a larger tip. Photos of the era show a lot of over-pressurized small tips and a bunch of under-supplied big tips. The few times crews actually shut down to change to the next size tip were few and far between, just like today--with stacked tips on master streams. If the first tip used is not the correct tip used, it never will be. Smooth bore has more reach, better penetration and reaches the seat of the fire better, or so the fire instructors all say. Not if you don't have the water to fill the smallest tip on your stack! An automatic would have discharged the same amount of water, have better reach, have better penetration and would certainly reach the seat of the fire better—both early on and later. For the most part, the firefighters of that time knew a lot more about hydraulics than current day firefighters. Why? They had to. When all the new firefighter-friendly stuff started entering the service, firefighters stopped learning hydraulics. In many circles it is considered unnecessary. |
| Why Hydraulics? |
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Not convinced? Here are four questions grandpa can answer in his
head today in less than 30 seconds, but I bet few of our readers
can answer them. 1) Dual 800’ 2 1/2" lines in a forward lay from a 60 psi hydrant will supply ____ gpm at 20 psi to the pump. 2) A 300’ 2 1/2" line is wyed off into two 2 1/2" lines--one 200’ long the other 300’ long. What tips are needed and what is the engine pressure? 3) What do you need to pump to supply two 2 1/2" lines 400’ long supplying a portable monitor with a 1 3/4" tip? 4) What do you pump to a 600’ dual 2 1/2" line relay to an engine pumping a 1 1/4" master stream tip? Answers appear at the end of this article. So what is the point? Nothing really changes. You’re probably saying, "Who needs to know this stuff?" If you’re going down the road believing newer nozzles are better nozzles, you better have a good handle on hydraulics or you’re going to bury your department for the next 20 years on the next nozzle purchase. |
| Pump Operation |
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Almost every department in the country pumps one engine pressure
on all fires for good reasons. A pump pressure of 150 psi is the
most common. Departments that understand water movement through 1
1/2", 1 3/4" and 2" handlines might pump closer to
200 psi. Some departments only pump 100 or 125 psi to reduce the
reaction at the nozzle. The fact that it is easier has nothing to
do with its ability to fight fire. In fact, it reduces the
line’s ability to fight fire. Engine pressure has a direct
relationship to handline flow. Low pump pressure, low flow.
Another way to look at it is, low flow guarantees a big fire. Low
engine pressures are one of the main reasons fires get away from
us today. All new apparatus have dozens of pressure gauges to allow the rig to regulate pressure to each line. They exist primarily to help the engineer solve hydraulics problems. Some progressive departments spec flow meters only. The most progressive organizations spec flow and pressure gauges or instruments that do both. Why? Because some lines are going to require different pressures to attain differing flows, depending on line size, line length and desired flow. How do you set all of the different pressures? You simply pump the highest required engine pressure and gate back all of the other lines. Right? Wrong. That is the textbook answer, but the real world fireground answer is totally different. The rig with flow meters operates a little differently. The concept is simply to throttle up until each flow meter reads what you want it to read and then adjust the individual gate valves to regulate flow between lines. Right? Wrong. That is also a textbook answer with no chance of working on a multiple line fire. |
| Pressure Gauges |
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Why won’t either example work? Because firefighting is not
static. Lines are constantly opening and closing. Try the
following pressure gauge-only example in your department and see
if it works. The first-in unit arrives and pulls a 150’ 1
3/4" attack line. The engineer throttles up to 150 psi. The
engineer goes on to another task. When the line starts flowing
water, the pump pressure drops to 130 psi. A sharp engineer looks
at the gauge and throttles up to make up for the difference. If
the line is constantly opening and closing, it won’t be
noticed. If not, the line continues to operate underpowered. If
the engineer throttles up and comes back to the panel later, he
will probably see a reading of 175 psi because the line is shut
off. So he will throttle down and the crew will continue on
underpowered. The 150’ line was suppose to flow 147 gpm; now it flows 114 gpm. If command wanted a 1 1/2" attack line, it would have been ordered. Now, the crews haul around the extra weight of the 1 3/4" line but don’t get the water flow required to get the job done. The IC now asks for another attack line. Another crew pulls a 250’ 1 3/4" line. They call for water, and the engineer charges the line. In some cases, the engineer will not throttle up. The new line will be underpowered and the original crews will experience another drop in flow. The pump pressure will drop to 110 psi. The original line only has 66 gpm and the 250’ line 51 gpm. It is easy to see why lines are forced to withdrawal on multiple line jobs where the engineer is only working with half of his brain. Take a look at Table 1. A sharp engineer will throttle up to maintain the 150 psi to his department’s SOPs. A great engineer is suppose to maintain 150 psi on the short line and 185 psi on the long line; that way both will flow 150 gpm. So, as the engineer throttles up, he gates back on the first line. In fact, he closes it off without reducing the pressure. How could he do that? Because the attack line wasn’t flowing water when he gated back, the gauge still reads 185 psi. Then all of a sudden the first line drops to zero, so he yanks the gate all the way open. The second line loses water and now two crews are screaming at him on the radio about not having any water. Next thing you know the chief is coming to the panel to give a short four-letter speech on leaving the pump alone when guys are inside. You don’t need too many of those speeches in a career to learn to pump one pressure all the time and leave the pump alone. If left alone, the hose crews and the pump operator will battle even more. While gating back the first attack line, the hose crew only has the nozzle partially open while they advance. When they reach their objective, they pull back on the handle and the flow and pressure do not increase. The pump operator has artificially restricted their flow. Eventually, if both lines are left open long enough a master engine pressure of 185 psi will be achieved and the first line can be gated down to 150 psi. Then one or both of the lines will be shut down and the engine pressure will jump to 215 psi. The engineer will eventually see the high reading and back the pressure down. When both lines open again they will be sitting around 140 psi. When the long line is shut down, the short lines crew will experience a jump in nozzle reaction and flow that will be harder to handle because all of the pump’s energy is now applied to their line. Make this a garden apartment fire with four to six handlines out and crews in positions where they need their flow, and you have a real problem. Is it possible to regulate four to six lines? Not really! If you’re operating in the so-called modern format of a plumbed gun and three 150’ attack lines with a 15/16" tip on a 1 3/4" handline, a 1 1/8" tip on a 2 1/2" line and a 225 gpm automatic tip on a another 1 3/4" line, you’re going to need engine pressures of 100, 127, 71 and 218. How do you do that without killing the nozzleman? What if one shuts down? |
| Suicide Knob/Roulette Wheels |
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The innovation of the '60s and '70s, the pick-your-gpm wheel on
the nozzle--what some people call a roulette wheel or suicide
knob--makes it even more fun to be pump operator. A 1 1/2"
nozzle instead of having one flow now has options on the wheel of
30, 60, 95, 125 and 150 gpm. That is only a 2,700 percent
variation in friction loss per 100’ of hose. A 1 3/4 or
2" line could have any of the following options: 30, 60, 95,
125, 150, 175, 200, 225 or 250 gpm. How do you deal with an unknown friction loss? You only use one setting. I know we’ve all heard it, but it isn’t true. The ring is wherever it ended up. In the dark, you’re totally lost as to flow settings. Ask the guys in the station to recite the flow settings of each type of nozzle--which way the wheel turns and what setting each line is currently in. I bet you will find nozzles stored in every position including flush. Some of the lower quality nozzles change flow when the operator changes from straight stream to fog and back. |
| Flow Meters |
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What changes with a flow meter? Go out and try this on your
engine. The first attack line is pulled and the pump operator
opens the line and throttles up. The flow meter reads between 100
and 300 gpm, while the line charges and then it reads zero. Why?
The line is not flowing. The line is eventually opened, and the
crew opens the line partially. The next thing you know, the
engineer is pumping 250 psi trying to shove 150 gpm through a
partially opened nozzle. When the nozzle is closed, the pump
pressure jumps to 350 psi. The engineer will go through the same challenge that the rig with the pressure-gauge-only panel went through. The line will drop in flow and pressure once it starts flowing water. If the drop is noticed, the line will be throttled up. If not, the line will continue underpowered. If the line is finally opened all the way and the engineer just happens to be at the panel, then the flow is set by advancing the throttle. As long as the throttle is left alone, everything is fine. In reality, everyone knows you need to pump a certain pressure determined on the training ground or someone’s view of what is proper, and every once in awhile the flow meter will actually read the desired flow. All it really tells you is you are flowing water. When the second line is pulled, you’re no better off than you were with the pressure gauge setup. Constantly opening and closing nozzles, partially open lines, kinks in the line, suicide knobs in any of three to six settings and clogged nozzles all cloud the correct throttle setting by flow meter. In the end, you hope you’re pumping pretty close to what everyone on the fireground wanted. Many departments using flow meters still pump 150 psi no matter what. No one ever talks about what happens when the line is burned through in the course of combat like ocurred in Pittsburgh and Chesapeake, Va. In concept, the pump operator would be watching the flow meter and would have throttled down because too much water would be flowing out of the open butt. Don’t allow the people controlling the purse strings to risk your tail saving a few cents by buying fire hose that can burn in two! That is what perfomance specing and grievances are for. If all else fails, break into the coffee fund and pitch in. |
| Playing with the Ring |
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What happens when the firefighter decides to change from one
setting to another? Let’s say a 1 3/4" line is being
supplied for a 200 gpm flow through a 150' line. The firefighter
at the nozzle decides that a 150-gpm setting would be easier to
hold so flow is selected without notifying the pump operator.
What is the flow and what happened to reaction? Originally, a reaction force of 101 pounds was being controlled by the nozzle crew. Now with the nozzle ring set at 150 psi, a flow of 169 gpm is moving through the line and the reaction is 96 pounds. Not much really changed in the way of making the line easier to hold. When the nozzle is shifted to 125 gpm, it flows 150 gpm and the reaction goes to 75 pounds. Finally, the reaction drops. All the IC can hope for is that the fire is the same size as the nozzle crew’s flow preference. As you can see in the above examples, flow rings on a nozzle don’t really flow what is stamped on them unless the pump operator is in sync with the nozzle crew. What is worse is to have the nozzle at a higher setting and have the engineer pump the lower setting. If the firefighter at the nozzle remembers to turn the ring, everything is fine; if not, you work with a weak stream. It is easy to see with a flow meter, pressure gauge or combination pressure gauge and flow meter equipped apparatus that pumping one predetermined engine pressure is the easiest and close-enough method to achieve a few workable streams. As long as they are all within 50’ in length of one another, all the same diameter, all have the same flow nozzle, and nobody is really putting their tail on the line behind them. In other words, the everyday no brainer fire. |
| Table 1- 150' 1 3/4" Attack Line | |||||
| Nozzle reaction with a | |||||
| 20 psi EP Bump |
40 psi EP Bump |
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| Original Nozzle | NP/GPM/NR | NR | NR | New GPM | New NP |
| Fixed Flow | 100/250/126 | 136lbs | 147lbs | 260/270 | 108/117 |
| Smooth Bore | 45/250/85 | 96lbs | 105lbs | 279/266 | 51/56 |
| Automatic | 100/250/126 | 134lbs | 142lbs | 266/282 | 100/100 |
| Answers: |
| 1) 291 gpm. |
| 2) 218 psi with 5 psi for the wye with 1 1/4" and 1" tips. |
| 3) 224 psi plus whatever you figure for the gun 5 psi per port used or 25 psi. |
| 4) 80 psi. |
| Larry H. Stevens is the editor of Fire-Rescue Magazine. CONTINUE TO PART 2 |
