So, even if the desire is to flow more water on the fire in the first place, human nature and common sense calls for the reaction force to be reduced to a safer level, which will always cause a reduction in flow rate.
Since nozzle reaction is generated by a combination of the weight of the water flowing (gpm) and the pressure at which it exits the tip, if it is desired to maintain or increase the flow rate, the only way to reduce reaction force is to either reduce the flow rate or reduce the nozzle operating pressure.
Once this fact is realized, it is a simple matter to evaluate two nozzle types--smooth-bore and low-pressure combination--in order to provide more flow rate at safer reaction forces. If it is determined that it may be desirable to stay with the same attack line hose sizes that are presently in service, testing can be concentrated on maximizing flows by selecting suitable, low-reaction-force nozzles.
By simply changing nozzle styles, pump pressures can be materially reduced over those needed to supply the same or increased flows than when using nozzles that operate at 100 psi. On the other hand, if the same engine pressures are used, low pressure nozzles will increase the flow rate.
When using 1-1/2-inch hose, friction loss is the only factor that limits the flow rate and length of hoselines. But, most standard friction loss charts list figures for friction losses in 1-1/2-inch hoseliness that may result in erroneous results. I think that the reason for the high friction loss numbers in these charts is that most of the research and study of friction loss occurring in the past 20 years has been concentrated on 1-3/4-inch and larger lines.
Since the 1-1/2-inch size has largely been ignored and considered old fashioned, industry developments such as thinner, high strength hose linings and thinner, high technology woven jackets (advances that have revolutionized and reduced the friction loss figures for other hose sizes), have not been properly and timely calculated for 1-1/2-inch hose, even though these improvements have been incorporated in the construction of this hose size as well. For example, for almost 10 years, the internal diameter of 1-1/2-inch size hose has actually been 1-5/8-inch or larger, attributable in part to thinner hose wall materials.
In actual practice, 1-1/2-inch hose coupled with nozzles that operate at pressures between 50 and 75 psi, flows up to 160 gpm can be obtained relatively easily.
For example, after extensive testing, the Detroit Fire Department decided to remain with 1-1/2-inch hose but upgraded their nozzles to low pressure versions flowing 125 gpm at 75 psi. This provides them with a mobile line that can be maneuvered and moved quickly by a single firefighter.
Another question I ask when evaluating attack hoseliness is if the department continually has problems with the fire not going out. Sounds like a simple question, but if there is no problem with the available flow rate doing its job, and if the available firefighters can easily handle the line, is there any reason to change?
Because of the limited flow of all common diameter attack hand lines, 1-1/2-inch, 1-3/4-inch or 2-inch, it must be remembered, that these lines are not all-purpose, all-fire, all-use devices. If the size of the fire dictates, use a larger line or bring in the heavy artillery.
It is certainly more cost-effective to re-equip present 1-1/2-inch hoseliness with higher flow, low pressure nozzles than to purchase new hose. To make the new hose work properly, it's a good bet that new nozzles will have to be purchased eventually, so it makes sense to evaluate them first, and maybe you'll find that new hose will not have to be purchased after all-that is unless you just want to impress the neighbors.