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.
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 the effects of a 15⁄16-inch smooth bore nozzle and a 11⁄8-inch nozzle operating at just 10 psi above and below the 50-psi mark.
As written about in many fire department pumping handbooks, the goal of the pump operator is to supply the nozzle team with the correct flow rate and nozzle pressure each and every time to maintain a nozzle at its optimal point of performance. It is with this in mind that we will begin to evaluate our limited ability to ensure nozzle teams have a workable nozzle using only a psi gauge.
Operations using PSI Gauges
If you look at the new deliveries section on any fire apparatus manufacturer’s Web site, you are sure to find that the majority of pump panels feature discharge outlets monitored only by psi gauges. The ability to measure only psi at the discharge outlet forces the pump operator to consider many factors such as friction loss, elevation loss/gain, and the number of hose sections within a hose layout when determining proper pump discharge pressure. In addition to these commonly thought of factors, there are factors that are nearly impossible for the pump operator to know during a fire. These unfamiliar factors include the friction loss coefficient of individual sections of hose and the pressure loss of discharge piping beyond the psi gauge. Putting together all these factors can affect nozzle characteristics discussed earlier in this article.
Limitations of psi Gauges Monitoring Discharge Outlets
Let’s take an example and say a nozzle team is stretching a line off the rear hosebed. The pump operator has just finished establishing a continuous water supply and now meets up with one of the firefighters, who is breaking the connection and hooking the line up to a discharge outlet. The firefighter states the line features a 15⁄16-inch (185 gpm at 50 psi) smooth bore nozzle and “thinks” the line contains five sections of 1¾-inch hose. Unfortunately for the pump operator and the nozzle team, the line only contains four sections of 1¾-inch hose. This misinformation causes the pump operator to overpressurize the hoseline by 25 psi because the pump operator believes the hoseline contains five sections of hose. The resulting pressure causes the nozzle pressure to be increased above the optimal operating point and results in a more difficult nozzle for the nozzle team to control as shown in Table 3.
Now, it is not a stretch to envision a few readers taking a moment and saying the nozzle team could just have the pump operator decrease the pressure in the hoseline. This is true, but even this so-called solution leads to more questions at an already stress-filled fireground. These new questions include: Will the nozzle team have the experience and training to recognize an overpressurized nozzle? If the nozzle team recognizes an overpressured nozzle, by how much should the pump operator decrease the pressure? 10 psi? 20 psi? 30 psi? And even if the nozzle team recognizes a problem, will some nozzle teams just choose to fight through a difficult nozzle condition, causing additional work, fatigue, and strain on the crew? And finally, how can the pump operator verify he is supplying proper volume and pressure to a nozzle without the nozzle team providing direct feedback?
As you can see, knowing only the psi reading at the discharge outlet for a hoseline leaves the pump operator unable to verify if the nozzle team has a properly charged, workable hoseline.
Next, we will look at using flow meters, in addition to our current psi gauges, to assist our pump operators with solving many of the problems mentioned above.
Advantages of Flow Meters
Flow meters take advantage of the fact that when water flows through a hoseline, that flow is consistent throughout the line. For example, if a nozzle team is discharging 185 gpm from a nozzle, that flow of 185 gpm can be measured not only at the nozzle but also at any point in the hoseline including at the discharge outlet where a flow meter is typically located to monitor a hoseline (Figure 1). This additional information provided by a flow meter gives the pump operator great insight into if a nozzle is operating at its optimal point. Capitalizing on this advantage found in flow meters along with implementing department-standardized nozzle packages and basic firefighter training leads to nozzle teams being able to operate in a safer, more efficient, and more effective manner.
Before we revisit our previous example involving the overpressurized 15⁄16-inch smooth bore nozzle, let’s take a moment to define department-standardized nozzle packages and outline the basic firefighter training needed to take full advantage of a discharge outlet featuring both a gpm gauge and a psi gauge.
Standardized Nozzle Packages
Department-standardized nozzle packages set the expectation for correct flow rate and nozzle pressure from a given nozzle size. A fire department may establish, through a department policy or training program, that:
- All 1¾-inch hoselines will feature a nozzle that will flow 185 gpm at 50 psi.
- All 2½-inch hoselines will feature a nozzle that will flow 265 gpm at 50 psi.
These flow rates and nozzle pressures should again be established through research and hands-on training performed by department members to find nozzle packages that work within their department. These nozzle packages should account for many factors, including target flow rate, reduced nozzle reaction, effective horizontal reach of the fire stream, available personnel, and the experience/training level of your firefighters.
By establishing a department standard on nozzle packages, the pump operator and nozzle team now can clearly communicate and understand what nozzle is being used. Radio transmissions such as “charge the 1¾ line” instantly allow the pump operator to know appropriate nozzle pressure and, more importantly, the corresponding gpm reading that should be seen on the pump panel anytime the nozzle is fully opened and flowing water.
Training: the Nozzle Team and the Pump Operator
The second portion of maximizing the usefulness of a flow meter falls to training when a nozzle team bleeds a hoseline prior to fire attack. Normally firefighters at the nozzle are taught to bleed a hoseline to remove residual air, check the quality of the fire stream, and verify the nozzle is discharging an appropriate flow rate. Many fire training videos and articles have presented the problem and dangers associated with a nozzle team not having a hoseline that can flow adequate gpm to combat rapidly evolving interior fire events.
The solution falls to the pump operator having the ability to check a flow meter when the nozzle team is bleeding the hoseline. This check must be done with the nozzle fully open to allow the pump operator to correctly adjust the discharge valve on the pumper to supply the correct flow rate to the nozzle. With effective training, this procedure can be completed quickly with minimal to no delay before transitioning to fire attack.
Revisiting Our OverPressurized Nozzle
Now that we have looked at both department-standardized nozzle packages and basic firefighter training, lets take another look at our previous example where the pump operator was supplying the hoseline with 25 psi more than our newly established department standard.
Just as before, the pump operator duties for calculating pump discharge pressure (PDP) remain the same. Calculating the initial PDP provides a good starting point when the nozzle team initially calls for water. The change occurs when the pump operator charges the hoseline to the calculated PDP and the nozzle team begins to bleed the hoseline.
At this point, the pump operator sees the gpm gauge for the hoseline is reading 226 gpm. Knowing the nozzle team is operating a 15⁄16-inch smooth bore nozzle, the pump operator was expecting to see the hoseline discharging approximately 185 gpm. Taking advantage of the nozzle team flowing water, the pump operator closes the discharge valve via a crank handle to reduce the pressure and flow rate reaching the nozzle to the department standard of 185 gpm, thus creating 50-psi nozzle pressure with a reaction force of 69 pounds and a horizontal reach of 59 feet. With this simple adjustment at the pump panel, the nozzle team will have a workable nozzle with an adequate flow rate, a reasonable nozzle reaction, and a quality fire stream.
As shown above, having discharge outlets that feature both a flow meter and a psi gauge not only benefits the pump operator with delivering the correct pressure and flow rate to the nozzle team but also gives the nozzle team a workable nozzle and fire stream.
1. Pumping Apparatus DRIVER/OPERATOR Handbook, 2nd Edition, IFSTA, page 166
SB Nozzle GPM = 29.72 * d^2 * sqrt(NP).
2. Pumping Apparatus DRIVER/OPERATOR Handbook, 2nd Edition, IFSTA, page 178
SB Nozzle Reaction = 1.57 * d^2 * NP.
3. “The Missing Tip” and Optimum Handline Flow in 2 ½-inch Hose, Dennis J. Le Gear, SB Nozzle Horizontal Reach = ½ * NP +26; add 5 feet for every 1⁄8-inch over ¾-inch tip diameter.
WILLIAM R. EMERY has been involved in the fire service since 2003. His career began with a volunteer fire department and he now works as a career firefighter with the West Allis (WI) Fire Department.