"I'm happy with what I have, so why confuse me with another hose size?" While there have been hundreds of thousands of discussions throughout the fire service on, for example, the flow merits of one nozzle or the penetration qualities of another, it must be understood that the most important...
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Many fire departments that feel uncomfortable operating with smooth-bore nozzles are opting for combination nozzles that are designed to operate at pressures as low as 50 psi. Many large cities such as Boston, Miami, Chicago, Los Angeles, Phoenix and Memphis, TN, have switched to low pressure nozzles for offensive attack operations. A review of the reaction forces of various nozzles that can be effectively paired with two-inch attack lines, shows why.
|200 gpm at 75 psi Nozzle|
|Hose Length||170 gpm||240 gpm|
|150 feet||75 psi||140 psi|
|200 feet||80 psi||152 psi|
|250 feet||85 psi||165 psi|
|300 feet||90 psi||180 psi|
|250 gpm at 50 psi Nozzle|
|Hose Length||210 gpm||250 gpm|
|150 feet||80 psi||110 psi|
|200 feet||95 psi||125 psi|
|250 feet||110 psi||150 psi|
|300 feet||125 psi||170 psi|
|Hose Length||1" tip (200 gpm)||1 1/8" tip (250 gpm)|
|150 feet||90 psi||105 psi|
|200 feet||105 psi||125 psi|
|250 feet||120 psi||145 psi|
|300 feet||135 psi||165 psi|
Let's assume for general attack operations it is desired to flow about 160 gpm. It can be seen by the chart on page 135 that a low-pressure nozzle rated 200 at 75 psi can deliver this flow while generating a relatively easily handled reaction force of only 64 pounds/force reaction. If 160 gpm is the only flow desired, the 15/16-inch tip can provide acceptable streams up to about 180 gpm, it must be kept in mind that since the main reason for changing to two-inch hose in the first place is to provide flows that parallel those obtained from 2 1/2-inch lines, attempting to flow more water through the 1 5/16-inch tip will not be successful because streams from smooth-bores begin losing their reach and generating high nozzle reaction forces at nozzle pressures over 65 psi.
One advantage to operating with a low-pressure combination nozzle is that the stream quality in flow ranges from 150 to 250 gpm is extremely good, even though nozzle pressures may vary. This means that with a little planning, a beginning pump pressure can be sent that provides, for example, a flow rate of 170 gpm. This insures that the interior crew can easily maneuver and safely operate the line yet still flow enough water to handle about three to four rooms of fire. If more water is needed, the supervisor can radio the pump operator to provide more pressure that will allow the interior crew to flow more water without having to stop the attack to change nozzle tips.
Photo by David P. Fornell
More and more fire departments that protect rural areas are taking advantage of the two-inch line's compactness and "user friendliness" when flowing big water. Wyocena, WI, equipped its new tanker/pumper with a 200-foot "heavy hit line" designed to flow 250 gpm through a 250-gpm at 50-psi low-pressure combination nozzle.
Operating pressures can be determined beforehand and the needed engine pressures marked on individual line pressure gauges with 1/8-inch automotive pin-striping tape available at any auto parts store. For example, the Memphis Fire Department marks its gauges in two increments. One line, in red, gives the operator the pressure needed to flow 170 gpm on pre-connected attack lines. A second line, in blue, indicates the pump pressure needed to flow 240 gpm on the same line. During an attack operation, if the officer feels that more flow is needed, he or she will radio the pump operator to increase the pressure to "blue-two." Since the pressure will not be increased until called for, the officer has time to prepare the crew to handle the increase in nozzle reaction, which is approximately equal to that of a 100-psi nozzle flowing the same amount of water on a 2 1/2-inch line.
This procedure has the decided advantage of having the increased flow rate immediately available on the line working the fire without the time-delay of having to stretch a second line. Since the day-to-day flow of 170 gpm is used most often, it is provided at only 64 pounds/force reaction, whereas under the old system the nozzle generated a hard-to-handle 84 pounds/force reaction.