| MASTER STREAMS |
| Part 2: Communications Are Essential |
| By Larry H. Stevens |
| Editor's Note: This is the second installment of our three-part feature on nozzles. In the March issue, we talked about the history of nozzles, flow meters and pressure gauge limitations. We also discussed how impossible it is for the pump operator to maintain a number of pump pressures due to a variety of fireground realities. This installment will discuss how new ideas have made it even harder on the pump operator and have transferred control to the nozzleman. Does the pump operator know that? |
| Do you still think this hydraulics stuff is a
bunch of bull? Let’s look at a portable master stream. Say
you bought one of the new ones with the big hose port. So you run
a 50’ length of 5" hose off your big discharge and
decide to flow it. What do you pump? Did you know that with one
of the master stream nozzles on the market a nozzle pressure
difference of only 20 psi will cause the gun to flow 200 gpm or
1,000 gpm? A 15 psi difference on another nozzle will result in a
1,500 gpm difference in flow? Consider that for every two gallons
leaving a nozzle, one pound of reaction is created, and you
don’t have to advance the throttle too far before the gun is
airborne. If the gun has a roulette wheel, you have a huge difference in flow and pump pressure requirements. In fact, if someone at the gun reduces the flow far enough, the gun can take off or the hose supplying the gun can break. Let’s say you’re pumping three 2 1/2" lines 100’ long to a 1,250-gpm monitor with the suicide knob set at 1,250 gpm. If the pump operator doesn’t have the relief valve set, and the firefighter at the nozzle changes the ring to 350 gpm, the pump is going to react as if a bunch of lines were shut off. An increase in pump pressure of a couple hundred pounds is a sure thing. Can a few pounds of pressure make a difference? You bet it can. |
| Smooth Bore Tips |
|
The smooth bore tip offers two things no other nozzle can provide
in normal use: a large flush capability and low nozzle reaction
for the flow achieved. Other than that it is just another nozzle.
The smooth bore promises high flows through large or small lines
at the lowest possible nozzle-and pump-discharge pressures.
According to the textbook, a nozzle pressure of 50 psi is
standard on a smooth bore handline and 80 psi is standard on a
master stream, vs. 100 psi for a fog tip in either use. Some
large departments use 45 psi on a handline. In Grandpa’s
day, 120 psi or more master stream tip pressures were preferred. Low pump pressure is often seen as a good thing. But with today’s modern diesel engines coupled to modern single-and two-stage pumps, engine rpms only vary 400 rpm between high idle and maximum flow capacity and pressures. The drive train isn’t burning any more fuel at 50 psi or 250 psi. Wear really isn’t an issue. Hose safety factors already sit at about 4-to-1 or more and with the best hose at 10-to-1. So we’re not really improving hose safety with lower engine pressures. If you’re going to use smooth bores, you’re going to need to learn hydraulics. Every tip has a different flow capability and friction loss for a given size hose. You won’t have a ring to read that tells you the tip’s flow unless you spec it as stamped on the tip. Departments utilizing smooth bore stacked tips have another version of the suicide knob. If you have a different tip in use than the engineer is pumping, you could go for a ride or be lucky to have any reach at all. |
| Kinking |
|
What is often overlooked by the smooth bore purist is kinking.
When you’re pumping ridiculously low smooth bore pump
pressures, kinking is a sure thing. A 1" tip flowing 210 gpm
on a 150’ 2 1/2" line results in a pump pressure of 63
psi. Unless you’re on top of the kinks, any expected
increase in flow with the smooth bore will be lost in a kinked
line. Worse yet, if you are pumping 63 psi and the kinks are like
those we see in front of buildings on the covers of magazines
just think how bad they will be inside. Eventually, someone calls on the radio and says to increase the pressure. If the engineer boosts the pressure 20 psi and the crew manages to pull the kink or kinks out of the hose, they are in for a difficult if not dangerous day at the nozzle. Instead of a low 50 psi tip pressure, they will end up with something closer to a master stream tip pressure of 67 psi with a flow of 241 gpm. The nozzle reaction will jump 35 percent. The instantaneous reaction forced when the kink is pulled out of the line will be almost 100 percent higher than with the kink. If you manage to hold on to the line, consider yourself lucky. Even small differences in nozzle pressure caused by kinks and poor pump operation doom the once-mobile line. How do you pump 63 psi? There is a good chance your supply line is operating at a higher pressure. You’re back to gating again. As more and more lines are pulled off the engine, you could end up with some wild variations of pump pressure. A 1 3/4" line 200’ long with a 15/16" tip will require a pump pressure of 156 psi. If the pump operator makes a mistake gating, there is a good chance someone is going to get hurt on the lower pressure line. If you use the "one pressure fits all" strategy, which pressure would you use? Would you use 63 psi or 156 psi? Would you split the difference? If you use fog nozzles and smooth bores then something between 200 psi and 63 psi would only guarantee that every line would be equally bad. Your pumper relief valve won't work under 75 psi. Don’t forget Grandpa--especially if you’re going to go to the so-called modern nozzles of his day. In the olden days, the engine supplying handlines never supplied master streams. In fact, the textbooks of the day specifically prohibited it. Why? Because if you shut off the flow of the master stream, the handlines go wild. The same is true when you mix and match high and low pump pressures. The same is also true when you mix and match smooth bores and fog tips. You are making a sure-fire investment on a wild line and getting someone hurt. What happens to the other attack line in everyday smooth bore operations when the first line is shut down? It gets an increase in pressure and flow. That negates the sales pitch of low nozzle reaction every time another line is opened and closed. It is not uncommon for firefighters, officers and fire service instructors to blame everything on the pump operator, when, in fact, most of the poor performance attributed to the operator can be associated with a bad buying decision. If you bought an unworkable mix of nozzles, you should expect surprises on the fire ground. When a 1 3/4" or the 2 1/2" line is shut down quickly, the other line experiences a 50 to 80 percent increase in reaction forces instantly and a 20 to 30 percent sustained increase. Whatever the smooth bore seemed to promise on the drill ground, it will rarely provide on the fire ground in a multi-line environment. Another concept that should not be lost in so-called modern nozzles is mixing smooth bore handlines with fogs. It is difficult to regulate a 50 psi difference between lines. Pressure relief valves will only absorb so much. By shutting down a fog tip, the guy on the smooth bore is going to see a large flow and nozzle reaction increase. If they’re ready for it, no problem. If not, expect a wild line or a line that is always gated back for safety. |
| Fog Nozzles |
|
The first question to ask a fixed-flow fog-nozzle user is what
flow did you select and why? You’ll see 125, 150, 175, 200
or 250 gpm models. Instead of buying a nozzle with a selector
ring with multiple flows, the new idea is to buy one nozzle with
one flow range and make do on all fires. If there was anything to
that thinking why did the fire service go away from that design
so many years ago? Is this possibly like the argument used by sales representatives to get you to buy a gas powered smoke ejector? They say you want to do positive pressure ventilation, you have to own a gas blower. Hog wash! Thousands of departments do it with electric blowers they already own. Maybe these sales reps think they can do it better with gas blowers. Oh yeah, how much better or faster? A similar argument is used for fixed flow nozzles. If you want to stray from NFPA standards and use a non-100 psi nozzle pressure nozzle, sales reps may say you must buy a new fixed flow combination fog nozzle. The story goes on that they are simpler, so there isn’t any maintenance. The sales pitch continues that there are nozzles failing all over America, and with fixed flow nozzles the pump operator maintains complete control of the flow and pressure so you are safer. The pump operator rarely has a clue beyond pre-set pump pressures for everyday lines. When you’re working with several different line lengths and sizes in conjunction with a variety of nozzles all flowing different amounts, add a few kinks, constantly opening and closing lines, and no engineer could possibly maintain the correct pressures. Do you really want the pump operator in complete control of your water? If you select a 150 gpm nozzle for use on 1 3/4" hose, you’re just 25 gpm over a 1 1/2" line. Is that really worth the added weight and cost over 1 1/2" hose? Is 150 gpm enough to deal with all of your fires, or will it require pulling a 2 1/2" line on any fire of size? Will your crew size allow the use of the 2 1/2" in aggressive combat on a first or second floor fire? Why not select a 175 or 200 gpm tip? Better yet, you already own a number of nozzles in the department that do the same thing. New? Hardly. In almost every case, the nozzle decision is based on what’s easy, or the easiest line for one firefighter to hold or advance. The decision should be based on fire volume. Not the everyday fire, but all fire the crew or crews might be faced with. The decision on nozzle flow should take into account the flow one firefighter can control and advance alone, as well as providing growth for two, three or more firefighters on the line. One flow does not fit all. |
| Low Pressure Nozzles |
|
Often sold as a new idea, the low pressure nozzle is another
gimmick that sells concept "easy." Over the years
we’ve seen the 80 psi fog, the 75, the 70, and even the 45
psi tip, while NFPA has stuck to 100 psi as the standard. Many of
these new tips throw awful looking streams. One rule of physics
that cannot be overlooked is when you reduce the pressure, you
always reduce the reach. For years fire departments figured in 70 or 80 psi nozzle pressures instead of 100 psi nozzle pressures into their hydraulics formulas to reduce nozzle reaction. Did it require a new nozzle to do that? No, just everyday hydraulics. A 2 1/2" breakapart playpipe, a type of nozzle, is tipped 1 1/2". So it is possible to remove the shut-off-equipped fog tip and use it on 1 3/4" hose. Many departments did just that. Then they figured a lower nozzle pressure, even though they left the nozzle in the 250 gpm setting on the flow ring. The end result was a flow of 209 or 224 gpm at 70 or 80 psi respectively. When the nozzle was set at 200, the flows were 167 or 179 gpm. Currently, departments buy low pressure versions of every type of nozzle built. Their old nozzle probably could have done the same thing, though, if the crews had a better understanding of hydraulics. |
| Mixed Tips |
|
Some departments began buying break apart standard- or
low-pressure fog nozzles with a small- or large-stub smooth bore
tip (depending on the concept) stored between the fog tip and the
shut off. Some manufacturers even started to build them into
their ball shut offs. Two concepts emerged: First, the emergency
low pressure concept was based on standpipe systems throughout
the country where the NFPA standards allowed 65 psi outlet
pressure. The system pressure was based on 100’ of 2
1/2" hose with a 1 1/8" 245 gpm smooth bore tip. Fire
services were converting to 1 1/2", 1 3/4" and 2"
standpipe packs at least for the first line and in many cases all
lines. The 65 psi system could not produce a fire stream through
the small fog-nozzle-equipped lines. If the stub tip was
5/8", it could flow a maximum of 81 gpm at 50 psi through
100’ of 1 1/2" hose. With 100’ of 1 3/4"
hose, a 11/16" tip at 50 psi would flow 97 gpm. A 100’
2" line could flow 137 gpm through a 13/16" tip at 50
psi. The standard seems too ridiculous for anyone to adopt this
concept, but that is what the system is capable of supplying to
code. If you’re using a larger tip on a 65 psi system,
you’d better go back and refigure your hydraulics. Any
standard fog tip on these systems would be horribly under
supplied and a real danger to the user. If you don’t try all
your systems before you buy the nozzle, you could be in for a big
surprise. The second concept for the small tip was to use it as a
low nozzle reaction overhaul or minimum staffing tip. The emergency high-flow stub tip was the more progressive of the two ideas. The concept was to have a high-flow fog tip backed by a higher-flow smooth-bore stub tip. The departments adopting this concept understand that the difference of 50 psi between the fog nozzle and the smooth bore can translate to increased flow. They know they can increase the flow out of the line without increasing pump pressure. (See Table 1.) This concept is not unlike a stacked tip on a master stream though; if you don’t shut down to change tips, you’re just packing extra weight and restricting the fire flow with the fog nozzle. |
| Automatic Nozzle Reach |
| It is a proven fact that smooth bore tips have better reach than fog nozzles. Right? Wrong. That statement is only true if the nozzle pressure is higher on the smooth bore than on the fog. At the same pressure, the reach is the same. When a 100 psi fog is compared to a 50 psi smooth bore, the smooth bore always loses. As long as a nozzle is used in the earth’s atmosphere that will be true. No new change in nozzle design will ever change that fact. |
| Table 1 |
| All lines 150' | ||||
| Hose Size | EP | 100 psi Fog Flow | Smooth Bore Flow | Flow Increase |
| 1 1/2" | 150 | 125 | 7/8"/160 gpm | 35 gpm |
| 200 | 175 | <1"/210 gpm | 35 gpm | |
| 1 3/4" | 150 | 150 | 1"/210 gpm | 60 gpm |
| 200 | 210 | 1 1/8"/254 gpm | 44 gpm | |
| 2" | 150 | 205 | 1 1/8"/265 gpm | 60 gpm |
| 200 | 290 | 1 1/2"/577 gpm | 35 gpm | |
| 2 1/1" | 125 | 290 | 1 3/8"/500 gpm | 210 gpm |
| 150 | 410 | 1 1/2"/577 gpm | 167 gpm | |
| Larry H. Stevens is the editor of Fire-Rescue Magazine. | CONTINUE TO PART 3 |
