By William R. Emery
Today, most fire department pumpers feature only pounds-per-square-inch (psi) gauges to monitor each discharge outlet.
Although using these psi gauges in conjunction with calculating friction loss within a particular hose layout has been common in the fire service for many years, it is time for the fire service to seriously consider integrating flow meters into each of its discharge outlets to create a safer, more efficient, and more effective fireground.
To look at the benefits of adding flow meters to our discharge outlets, let’s take a moment to review the principle characteristics of a workable nozzle and the difficulties in verifying if a nozzle is receiving proper pressure and flow rate using only psi gauges.
Optimal Nozzle Characteristics
Like many tools, a nozzle has an optimal point of performance. This optimal point typically reflects research and hands-on training performed by departments to find nozzle characteristics that work within their department. Some common nozzle characteristics that your department may focus on are as follows:
- Target flow rate.
- Reasonable nozzle reaction.
- Fire stream quality.
- Horizontal reach of the fire stream.
Fire departments will balance the positives and negatives of each nozzle characteristic and will generally publish, through a department policy or training program, the optimal point to operate a particular nozzle. For example, a department may choose to operate all 1¾-inch handlines with 15⁄16-inch smooth bore nozzles flowing 185 gallons per minute (gpm) at 50 psi, creating 69 pounds of force (lbf) of nozzle reaction and 59 feet of horizontal reach.
1 Commonly fire department pumpers have included psi gauges and push/pull “T” handles to monitor and control the flow to hoselines. (Photos by author.)
From this point, it is important to understand that the farther away a nozzle operates from the department-established optimal point, the less efficient and effective the nozzle becomes for the nozzle team to operate. Table 1 highlights some of the pitfalls associated with smooth bore nozzles operating above or below their optimal points. As shown, operating below the optimal point can endanger the nozzle team with a fire stream that does not have an adequate flow rate. Equally troubling is an overpressured nozzle that will have increased nozzle reaction, causing additional work, fatigue, and even possible safety concerns.
To bring in specific values to highlight the previous point, Table 2 shows