Driver-Engineers Debate: This One Or That One?


Driver-engineers (D-Es) directly control how much water goes on the fire and how quickly it will get there. The fire pump of the first-due engine is the heart of the fireground. If every part works as it should, the fire will go out quickly and effectively. If the pump breaks down, the fire wins; property is lost and, in the worst scenario, lives are lost. Much like arteries and veins and blood circulating through the body, the fire pump’s network of intake valves and discharge valves helps move water from static sources to the fire and allows D-Es to perform their job.

The apparatus and equipment used change and vary depending on the department, standard operating procedures, and city budgets. There are many apparatus, tools, and equipment from which to chose, and no one tool or truck is right for every situation. With all the latest technology in apparatus design, pump panel layout, and hose and nozzle selection, D-Es debate about their favorites. Debatable subjects include choices of pump panel positions and layouts, single- vs. dual-stage pumps, pressure governors, and nozzle selection for bread-and-butter operations. This article provides insight into these subjects and feedback from experienced engineers still on the job. If you were to ask the engineers in your department what they prefer with regard to the items below, you most likely would get a different answer from each.

Six senior D-Es, members of the Fort Lauderdale (FL) Fire Department, whose experience levels range from 10 years to more than 20 years, were asked to participate in this project. (Note: Their opinions do not reflect the preferences of the entire department. Their comments were examples I used to compare against the information I found in my research for this article. That is what makes our profession so interesting: There is always more than one way to put out the fire!)


Some D-Es may have input concerning the apparatus their departments purchase, especially if they sit on an apparatus selection committee. But, most have to “take the good with the bad” and adapt to whatever type of pumper the department chooses. Bugetary constraints generally determine what is purchased in many departments.

Top-mount pump panels have some advantages and disadvantages. Following are some things to think about the next time you have a chance to make a difference in the type of pump your department purchases.


  • Better operator position: Top-mount pump panels position the operator on the top of the vehicle, giving the D-E a panoramic view of the fireground. If something goes wrong on scene, the D-E most likely will see it happen and can notify command-i.e., a roof collapse or the loss of the water supply. From a safety perspective, the D-E is out of traffic and away from other firefighters working and retrieving equipment from compartments. When working on a highway, the D-E is less exposed to oncoming traffic and is less likely to be hit by another vehicle.
  • Increased body space: Moving the pump up front increases space for larger water tanks, more compartments, and longer ladders. Most mid-mount pumps need four feet or more of frame length across the entire width of the truck. This space cannot be used only for the pump assembly.
  • Easier drafting: Drafting operations are easier with the pump near the front of the vehicle, where it can be positioned close to the water source. In some cases, it is also much safer because the D-E can ease the front end close to the water’s edge while keeping the main weight of the vehicle farther back on more solid ground.


  • Operator position safety: Safety is an issue here. Some D-Es argue that because you are not attached to the pump with a harness or a belt, you could easily be thrown from the apparatus and fall into traffic or another firefighter. This is especially true if you are operating on a highway and your engine is struck from behind or laterally while you are working on the pump panel.
  • Engine noise: With a top-mount pump, the D-E stands closer to the engine than with some side-mount pumps. The piping and pump assembly usually sit directly under the pump panel. Depending on the engine noise level, this may be a concern, and the firefighter may require hearing protection.
  • Limited mobility: Top-mount pumps are mounted inside the body of the vehicle and are powered through a split-shaft transfer case. Engine power is directed from the wheels to the pump when the pump is operating. This type of pump offers the greatest pumping capacity, but the apparatus cannot move while the pump is engaged. Unlike a crash-rescue fire truck, these engines do not feature pump-and-roll capability. Therefore, the top-mount is most common in structural pumpers, since this type of fire requires the most water and little mobility.


Side-mounted pump panels are by far the most popular based on my research and the feedback from the D-Es.


  • Operation: The D-Es like being able to “feel” the water moving in and out of the truck. If the gauges are not working correctly, they are able to make immediate adjustments based solely on the feel of the pump water. They state they can “listen” to the truck better than if they were on top of the engine.
  • Draftng operations: The D-Es said they are able to watch the suction hose close up instead of monitoring its operation from a top-mount pumper. The downside to this is that the D-E cannot leave the panel for more than a few moments. If your department has minimal staffing, the additional tasks peformed on the fireground by the D-E-hose deployment, throwing ladders-will have to be done by another firefighter because the D-E will have to stay and operate the pump panel.
  • Safety: The opportunity to slip and fall is greatly reduced when pumping from the side of the apparatus. In addition, the wear and tear on a D-E’s joints is reduced because it is not necessary to step up and down to do the job. Some of the more “seasoned” veteran drivers stress that everything can be done from the ground and argue that the top-mount is very dangerous because there is nothing to hold the D-E in place should another vehicle strike it in the rear or on the side; the D-E would be thrown off. Depending on the severity of the crash, the D-E may even be crushed. If electrical wires land on the truck (because it is parked the wrong way or in the wrong spot), the D-E on a top-mount pump panel would be stranded. On a side-mount pump, the D-E would be able to just walk away from the apparatus.
  • View of the fireground: Some D-Es argued that the D-E knows the district well enough that he should be able to respond to any address and have the pump panel facing the building. This is not always easy to do, especially when more apparatus are responding, the fire stations are only a few miles apart, and the units race to be first at the scene. One D-E recommended this street-smart tactic: “Open both cab doors for a clear view of the site to the other side of the engine and the fireground.”


A fire department must specify in the purchasing specifications the type of pumping equipment wanted. There are two basic models of centrifugal fire pumps from which to choose: the single-stage and the two-stage. The two-stage pump uses two impellers mounted side by side in a pump housing. Each of the impellers has an intake side and a discharge side, which are connected by a transfer valve. This valve determines how the stages of the pump will operate. Although D-Es may prefer one type of pump over the other, they do not make the purchasing decision.

A two-stage pump breaks down less frequently than a single-stage pump. My department has both types of pumps. The newer engines are single stage. The older engines are two-stage pumpers. The older engines are “work horses.” They not only pump great, but they also last longer than most of the single-stage pumpers in our fleet. The drivers surveyed for this article agree. Again, this information is department specific and is based on the community you serve.

Two-stage pumps are preferred for the following reasons:

  • Performance: Pumper performance is better with a two-stage pump over almost the entire operational range, meaning that whether we are pumping in pressure or volume, we will get the desired gpm with a two-stage pump vs. a single-stage one.
  • Efficiency: Two-stage pumps are more efficient at pumping required flow rates and capacity regardless of the type of fire.
  • Life: Two-stage pumps last longer than single-stage pumps, and they place less wear and tear on the engine, chassis, and driveline components.

Pump Performance

Today, 1,500- to 2,000-gallons per minute (gpm) pumpers are more common than the 500-gpm through the 1,250-gpm pumpers of the past. The majority of fire pumps installed today are single-stage; however, two-stage pumps, which have important advantages over single-stage regardless of the capacity rating, are overwhelmingly superior when the rating is 1,500-gpm or more.

The two-stage centrifugal pump works in either the pressure mode or the volume mode. When the pump is in the pressure mode, the water supply enters only one impeller. The water is then discharged to the intake of the second impeller. Where the pressure and velocity are greatly increased, the water then leaves the second impeller and is discharged to the discharge side of the pump. This mode is also known as “series operation” because the water movement is linear from impeller to impeller. The one drawback to this mode of operation is that the pump can create a high pressure, but the volume available is limited to half the capacity of the pump. A 1,000-gpm pump would be limited to approximately 500 gpm. This is a rule of thumb formula for volume vs. pressure.


Look at the apparatus in your fleet. When was the last time a pump flowed rated capacity at a fire call? For many departments (including the big ones), most fires are extinguished with one or two handlines flowing about 150 gpm. Two-stage pumps are really “two pumps in one.” When operated in the volume (parallel) position, they mimic the design of the single-stage pump.


The two-stage pump is more efficient at most flow rates, but what does that really mean? If you are using a single-stage pump to flow less than the rated capacity, it will spin faster than a two-stage pump. This will cause the pump to wear out faster. Finally, although single-stage pumps are designed to flow large volumes of water, they are not designed to produce high pressures. Using a two-stage pump to develop the same 125 gpm at 200 pounds per square inch (psi) requires about 25 percent less speed, which greatly reduces the amount of recirculation cavitation inside the pump.

For busy departments, this could result in an unexpected premature budget-busting pump overhaul job. More importantly, the faster you run a diesel engine, the more horsepower it will develop. This causes the engine to consume additional fuel. A typical diesel engine consumes about 20 gallons of fuel per hour when run at governed speed. This may not sound like much, but over the life of the apparatus and with today’s fuel prices, the dollars can add up quickly. The excess horsepower not used will be converted into heat energy, which will cause the water in the fire pump to heat up. If the water gets too hot, a catastrophic pump failure would be imminent. Also, running the engine faster than necessary will result in additional wear and tear on the engine components. A two-stage pump will decrease this wear and tear. So, the biggest advantage to using two-stage pumps is that they will last longer.

Single-Stage Pump Applications

A single-stage pump is easier to operate than a two-stage pump because the operator of the latter must decide whether to place the pump in volume or pressure. If more flow or pressure is required when operating a single-stage pump, the operator needs only to increase the engine speed. With a two-stage pump, the operator must transfer the pump from pressure to volume (or vice versa) to obtain the desired output; the engine speed must not necessarily be changed. This means that the operator can leave the pump in the pressure mode for the vast majority of working fires. On the rare occasion when more than 50 percent of rated capacity is required to extinguish the fire, the operator will quickly observe that not enough water is being pumped at full engine throttle and realize the need to transfer the pump to the volume mode. In fact, a two-stage pump most commonly is used to pump only a fraction of its rated capacity, usually at fairly low pressure, but often at pressures much higher than the 150 psi at which the rated capacity can be efficiently pumped.


Relief valves and pressure governors are used to prevent the transfer of excess water pressure to handlines and other hoselines. The relief valve and pressure governors are used primarily when more than one hoseline is in operation. If one nozzle is shut down, the excess pressure will be redirected to the hoseline still operating if the relief valve is not set. The pressure governor works differently, but the result is the same. The pressure governor is set based on engine speed. Once the pressure governor is set, the engine will speed up or slow down to match the highest pump pressure setting. The engineer must adjust the manual valve by hand for the highest pump pressure setting.

D-Es cannot make the fine adjustments in fuel and air balance required to minimize pollution coming out of the tailpipe. Since the throttle position was the only parameter the operator could adjust quickly, the engine was susceptible to running differently in various conditions (such as temperature). As a result, electronic systems were created in which the throttle position was just one input in controlling how the engine operated. The throttle position was changed into a digital signal that could be combined with other digital inputs to properly and efficiently improve the engine’s performance. Manufacturers found that electronically controlled engines would run more consistently and with less pollution. Primarily as a result of government regulation, starting in the mid-1990s, mechanically controlled engines were phased out and were no longer available on new trucks. At that time, almost all fire trucks were equipped with a direct throttle control paired with a discharge relief valve. Therefore, the logical approach was to replace the direct throttle control with the electronic throttle control. Other designers, however, took a different approach and created the first fully electronic pressure governors.

These governors have two operating modes. In revolutions-per-minute (rpm) mode, the governor maintains a constant engine speed. This is similar to the traditional throttle control, with an important exception: It will maintain that speed regardless of engine load. In pressure mode, the governor will adjust engine speed to maintain a preset pressure regardless of the pump flow. In effect, the governor combines the function of the throttle with that of the relief valve and accomplishes what the operator used to have to do. Specifically, it monitors pressure trends and compensates to keep things smooth. We have electronic governors in our department. The general consensus on this tool is positive. D-Es find the governor easy to use, as it automatically sets the pressure to the highest line with the push of a button instead of the D-E’s having to manually set it each time.

The pump governor system was proactive. It constantly monitored the discharge pressure and could make changes much faster than any operator. Some governors will not allow more than 10 psi of spike under the worst conditions. In addition, the operating information could be displayed more readily. The operator no longer had to assume that the relief valve was set correctly. He could tell at a glance what the discharge pressure set point was.


The nozzle has the greatest impact on whether there will be success or failure on the fireground. It dictates the technique the nozzleman will use. Whether to use a smoothbore or a fog nozzle is probably the most discussed topic in the fire service. The fire must be extinguished quickly for the safety of the attack crews and trapped occupants. The nozzle must have a quick knockdown punch, especially with new construction methods that have markedly decreased the time before a building’s integrity is compromised. A fast knockdown necessitates high attack flows that reach the seat of the fire with limited nozzle reaction and consistent safe application of the fire stream. To achieve this, a straight or solid stream and proper training are musts.

Reach and Penetration

Horizontal reach with an effective stream is important: The greater the distance between the fire and the attack crews, the better. The nozzle creates a restriction at the end of the waterway that changes water pressure to velocity. Velocity provides the reach to get the water to where it is needed.

The solid or smoothbore nozzle is very basic in design and function. It produces a solid stream that provides maximum reach and penetration. The solid bore stream produces a solid compact stream of water. This stream has great penetration because of its mass. The heat will not absorb it rapidly and will enable the water to reach the fuel source. When used properly, the solid stream produces less steam, gives faster knockdown, and uses less water. Since the water is applied directly to the fuel source, there is less thermal layer disruption, which provides better visibility. This stream is recommended when there is a well-ventilated fire. In many cases, the fire has already vented itself before your arrival. Generating steam within a confined area can prove detrimental and dangerous to all inside the structure. The most effective method for quick extinguishment and safety, I believe, is a direct attack using the straight stream or solid stream. Water applied in a fog pattern will turn to steam more quickly than water confined within a straight or solid stream. Using the indirect and combination attack will produce massive amounts of steam, which will negatively impact an aggressive interior attack. Overuse of water in any method can prove ineffective and create a hostile environment.

The fog stream has great heat absorption potential because of its high surface-to-mass ratio. As we have been taught, the fog stream is directed at the ceiling into the superheated gases and thermal layering. This action can disrupt the thermal layering. When using a fog stream in a combination attack, the heat and gases throughout the compartment blend, causing extreme heat and steam throughout. When the heat and gases are mixed, they will not separate and will create an extremely hot and dangerous atmosphere. With the fog stream, you do not have the penetration and reach that sometimes are necessary. An improperly used fog stream will tend to push fire into the unburned portions of a structure.

The Oakland (CA) Fire Department lost a member, Tracy Toomey, in 1999 during an aggressive interior attack. A Board of Inquiry was convened to investigate his death. The fire was in a two-story residential structure; heavy fire was showing on the first floor on arrival. The fire was not extinguished in time to prevent the loss of structural integrity, even though several attack lines were in place. All were fog nozzles. The Board of Inquiry report cited as one of the three direct causes of the line-of-duty death “the inability to flow sufficient water to extinguish the heavy fire encountered.”(5) The Board strongly urged that smoothbore nozzles be used on the department’s preconnects. Obviously, the critical flow rate with effective knockdown capabilities must be considered when choosing the proper nozzle for an aggressive interior attack.

Nozzle Reaction and Hose

The nozzle reaction ultimately decides effective fire flows for handlines. With high nozzle reaction, the nozzleman will probably do one of two things: gate down to deliver a lesser flow with more manageable reaction or lose control of the handline. Nozzle reaction is directly correlated to nozzle pressure and flow. The end result is nozzle reaction measured in pounds per force. A major benefit of a solid stream nozzle vs. a fog nozzle is that at equal flows, a solid stream nozzle typically produces one-third less nozzle reaction. This decrease in nozzle reaction has many advantages for the attack crew: ease of maneuverability of the nozzle; less fatigue, which reduces air consumption, enabling firefighters to aggressively attack the fire longer; and less chance that the nozzleman will gate down, thus achieving the critical flow rate to put out the fire.

Absorption Rate

Different situations require different methods of applying water or foam. Some situations require the reach and penetration of a straight stream, whereas others require the heat absorption capability or radiant heat protection of a wide-angle fog spray. Both the fog and solid streams have fire suppression advantages and disadvantages. There will always be a need for fog nozzles, such as for exposures, gas leaks, and Class B fires. These fog nozzles should remain on one or more of your engine’s preconnect attack lines. The fog stream has great heat absorption potential because of its high surface-to-mass ratio. Fog nozzles are ideal for areas with no ventilation or areas that are difficult to ventilate. Smoothbore nozzle streams will not be absorbed by the heat, which will allow water to reach the fuel source for extinguishment.

Maneuverability and Training

Many issues are associated with each nozzle. For instance, if there is a chance that debris will enter the nozzle, a smoothbore would be the choice nozzle because of its open design; the fog nozzle would have an ineffective stream. Another issue is hose kinks. There are two beliefs. One is that with the fog nozzle at 100 psi, the hose won’t kink, but it would be more difficult to move in smaller spaces. The opposite is true for a smoothbore nozzle: It would kink, but it would be easier to maneuver in confined areas.

Departments provide various amounts of training for the pump operator and the nozzle operator. The nozzle should complement the training. Solid bore nozzles require the least amount of training. The engine pressure depends mainly on the length and size of the hose. Single-gallonage or variable-pressure/variable-flow nozzles require somewhat more training. Adjustable-gallonage fog nozzles require additional training because different engine pressures are required for each of the flow settings of the different hose lengths and sizes. Automatic/constant-pressure fog nozzles also require additional training. The pump operator must be trained to accurately control the engine pressure and flow with hose of different lengths and sizes and under various operating conditions. Multipurpose nozzles require additional training because the nozzle operator must be able to use the different types of streams they provide


The problems can be broken down into three basic areas: supply, which consist of tank-to-pump operations and external water sources; pump, which range from neglecting to place the apparatus in “pump mode” to total engine failure; and discharge, which include everything from choosing the correct discharge outlet to identifying kinks, bursts, and blockages in the line. When things start to go wrong, first ask yourself, “Is this a supply, pump, or discharge problem?” If you can answer that question, you can eliminate two-thirds of the work you will have to do to find a solution.

You can readily identify two indicators of a supply problem while standing at the pump panel. The first is cavitation, which means you are trying to discharge more water than you have supplied. Cavitation can occur while operating from the onboard tank, at draft, from a water supply apparatus, or from a hydrant. If you hear what sounds like metal grinding against metal, that is the sound of cavitation. You would need to start thinking about supplying your truck with water.

Normally, when an apparatus arrives on scene and crews begin pulling lines, the onboard tank is used to charge the handlines, even if an external supply is readily available. As pump operations begin, if cavitation occurs, it usually begins when the throttle is applied to charge the first lines. There are many causes for cavitation; those most commonly associated with the booster tank are the following:

  • Air is entering the pump, causing prime to be lost.
  • The tank-to-pump valve is closed or is only partially open.
  • The tank refill/recirculating valve is open.
  • There is no water in the booster tank.

Next, check the tank refill/recirculating valve. Often, operators, out of habit, open or at least crack the refill/recirculating valve to prevent the pump from overheating. National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, states that a 500-gallon or more onboard booster tank must be able to supply a minimum of 500 gpm through its tank-to-pump line; tanks that hold less than 500 gallons must supply 250 gpm. When the refill/recirculating line is open, think of it as an additional discharge line, and when two handlines can easily flow 250 gpm each, even cracking the refill/recirculating valve may overcome the capacity of the tank-to-pump line. The solution is to make sure your supply, especially when limited by the tank-to-pump line, can meet the desired flow. Every D-E I have asked about this subject says the same thing: “The tank recirculation valve is left cracked open while flowing multiple lines. The thought is that the pump will constantly be kept cool and not overheat.”

The differing views concerning the above appliances will continue to exist. If you were allowed to carry only one forcible entry or ventilation tool, which would you carry? Would it work for every job? The same dilemma applies to nozzles, apparatus, pumps, and other firefighter tools. Every fire is different, and that one tool or apparatus may not be the best choice for every incident.


1. Connors, Todd (February 2006), “Building a Case for Implementing Smoothbore Nozzles,” Fire Engineering, Fair Lawn, NJ.

2. Cool, Troy (February 2005), ” ‘Interior’ indirect and combination attacks misunderstood,” Fire Engineering.

3. Flately, C, Knapp, J, Leihbacher, D, and Pillsworth, T. (October 2007), “How kinks affect your fire attack system,” Fire Engineering.

4. Fredericks, Andrew (February 2000), “Little drops of water: 50 years later, Part I,” Fire Engineering.

5. “Residential Fire Causes,” http://www.nfpa.orgs/research.

MARK J. ROSSI is the driver/engineer on Engine 46, A-shift, in the Fort Lauderdale (FL) Fire Department. A 14-year veteran of the fire service, he is a live fire training instructor in the areas of firefighter minimum standards, hydraulics, driver-engineer, aerial engineer, and firefighter survival for Coral Springs Fire Academy. He has a bachelor’s degree in finance and a master’s degree in business from the University of Florida.

More Fire Engineering Issue Articles
Fire Engineering Archives

No posts to display