For many years, the centrifugal pump has been the “workhorse” of fire pumps used on most fire apparatus in the U.S. and Canada. Let’s consider how that fact came to be.
The timeline of fire pumps in the fire service can be traced back to these critical points in history:
Fire pumps have been an integral part of the fire service and have continually evolved. Hand-operated cylinder-type pumps were replaced by the more efficient rotary pumps powered by steam and then by power take-off (PTO) from the apparatus motor. This evolution achieved more effective water pressures with ever-decreasing human effort.
Many firefighters and fire officers mistakenly believe that the pumping capacity of the pump (e.g., 750 or 1,500 gpm) is the most significant factor in a pumper’s ability to transfer water. The reality is that the horsepower of the pumper’s motor is the biggest factor.
The trend of progressively larger fire pumps corresponds to a rise in available reasonably priced truck engine horsepower, especially since the introduction of diesel motors to power fire apparatus.
FIRST MOTORIZED FIRE PUMPER STANDARD
The original vehicle-mounted fire pump rating system was developed by the now-defunct National Board of Fire Underwriters (NBFU), today known as the Insurance Services Office (ISO), and the International Association of Fire Engineers, now the International Association of Fire Chiefs (IAFC).
In its initial publication for a Class B pumper, the NBFU required 100% pump capacity at 120 psi net pump pressure (NPP), 50% at 200 psi NPP and 33.3% at 250 psi NPP.
ORIGINS OF THE CLASS A PUMPER
Between 1939 and 1947, national authorities on fire apparatus discussed the concept of a Class A pumper that would deliver 100% of its rated capacity at 150 psi NPP, 70% of rated capacity at 200 psi NPP, and 50% of rated capacity at 250 psi NPP.
When the NFBU issued its 1947 edition of its Suggested Specifications for Motor Fire Apparatus, it contained both the Class A pumper standards and those for Class B pumpers. By 1956, the specifications no longer included those for a Class B pumper.
As a result of this evolution, most pumpers built prior to 1939 were Class B, those built from 1939 through 1956 were either Class A or B, and those built since 1956 are Class A.
NFPA TAKES ON MOTORIZED FIRE PUMPER STANDARD
Today, pumper requirements are outlined in the NFPA 1901: Standard for Automotive Fire Apparatus. NFPA 1901 considers seven pump capacities as being standard for the fire service: 500 gpm, 750 gpm, 1,000 gpm, 1,250 gpm, 1,500 gpm, 1,750 gpm and 2,000 gpm.
Fire department purchase contracts today specify the required capacity of the fire pump. Pumps manufactured today must conform to the requirements of NFPA 1901 and are designed to meet the following discharge requirements:
- 100% of rated capacity at 150 psi NPP
- 70% of rated capacity at 200 psi NPP
- 50% of rated capacity at 250 psi NPP
By 1957, Class B ratings were discontinued, and all pumps were rated at Class A levels, as they are today. Why? Because engine power had increased.
INCREASED HORSEPOWER FOR BETTER FIREPOWER
The Class B standards served as a transition. According to Gene Mahoney, author of “Introduction to Fire Apparatus and Equipment”: “Records from Hale and American Fire Pump (Barton American) show the pumps did not change, even though the ratings changed. It was all about available engine power.”
According to Mahoney, from the 1920s to the early-1940s, Class B pumps (400 gpm to 600 gpm) dominated the fire pumper market. As the 1940s faded, the most common pump size had become the Class A (500 gpm).
THE DAWN OF THE DIESEL ENGINE FOR FIRE APPARATUS
In a 2010 article “History Brings Us to the 1,500-gpm Pump,” Gary Handwerk wrote of the impact that increased horsepower from diesel engines being used to power fire apparatus had a dramatic impact on increased pumping capacity: “Commercial truck engines commonly delivered 110 to 150 horsepower. By the mid-1960s, the 750-gpm-rated pump had become the big seller, and a trend began to appear as commercial engine power jumped into the 160 to 190 horsepower range.”
The 1970s saw the fire apparatus manufacturers transitioning from the use of gasoline engines to diesel engine, which provided more reasonably priced available horsepower.
In the early-1970s, a 350-hp diesel engine was the most popular engine used in custom fire apparatus chassis; the custom chassis could power a 1,500-gpm pump while a commercial chassis with a 220-hp gasoline engine would max out at being able to power a 1,000-gpm pump.
INCREASED HP MAKES FOR INCREASED GPM
By the end of the 1970s, the big engine in a custom chassis was 450 horsepower, and the commercial chassis had a 210- to 240-hp diesel.
The normal size fire pump also went up – from 750 gpm in the early-1970s to 1,000 gpm as the big seller, with 1,250 gpm growing in popularity.
The 1980s saw the 1,250-gpm pump become the norm. The size of the engine on a commercial chassis increased to 240 to 280 horsepower.
In the mid-1990s, the 300-plus-hp diesel engine had become the norm, and the fire service saw a corresponding increase to 1,500-gpm rated pumps.
BETTER DIESEL ENGINES
The trend continues to the present as engineering advancements (e.g., turbochargers) have improved diesel engine performance.
Curt Bennink, author of “50 Years of Equipment Impact: Five Decades of Diesel Engine Evolution,” described some of the key innovations that have shaped the modern diesel engine over the past 50 years.
According to Bennink, “There were several key innovations that substantially increased the efficiency and capabilities of today’s diesel engines. These include:
- Adoption of high-pressure common rail (HPCR) fuel systems and the EUI, commonly referred to as the electronic unit injector
- Introduction and advancements in turbocharging
- Development of electronic engine controls and sensors
- Adoption of charge-air cooling
- Implementation of cooled exhaust gas recirculation (EGR)
- Advent of the diesel particulate filter (DPF)
- Adoption of selective catalytic reduction (SCR)
- Implementation of telematics that allow customers to communicate with the engines
To this point, we’ve considered how centrifugal pumps became the primary type of pump used on most fire apparatus in the U.S. and Canada. But there are two equally important types of fire pumps that are gaining traction with fire department leaders: the PTO pump and the ultra-high-pressure (UHP) pump.
POWER-TAKE-OFF PUMPS
PTO-driven pumps are not just for wildland firefighting apparatus anymore. Several manufacturers, including Pierce Manufacturing and Rosenbauer, produce apparatus with PTO-driven pumps rated up to 1,500 gpm. PTO-driven pumps have several significant advantages for the buyer.
The cost of the pump is about 50% less than a midship pump.
The manifolding on these large PTO-driven pumps is quite simple and custom-designed, enabling manufacturers to prefabricate custom suction and discharge manifolds that meet the customer’s needs. The pump can literally tuck underneath the cab or immediately behind the cab, using often-wasted space.
PTO-driven pumps make for compact pump modules, and there may not be a need for a pump module at all, freeing up compartment space in the vehicle. They have easier operations because the apparatus operator engages the pump by merely pushing a button in the cab, regardless of whether the truck is in drive, neutral or park.
Additionally, these savings in weight and space dedicated solely to the pump and manifold can be a considerable advantage for fire departments when considering the needs for a pumper and a rescue truck – one vehicle for all emergency needs.
The pump-and-roll capability of a PTO-driven pump increases the firefighting capability of the apparatus, particularly during wildland interface operations to protect structures.
ULTRA-HIGH-PRESSURE PUMPS
Increasingly, fire departments are taking closer look at UHP pumps when specifying new fire apparatus or refurbishing existing apparatus.
Some “elder statesmen” may recall the first rendition of a high-pressure pump used on fire apparatus: The John Bean high-pressure pump design allows a deliver between 600 and 850 psi, producing a fog stream of smaller water particles than conventional fire streams. When changes occurred in building construction materials this led to hotter and quicker burning fires. As a result, the Bean high-pressure pump started to drop in popularity as the conventional wisdom became “more GPM means more fire suppression.”
So, what has changed? For starters, one needs to look no further than Chapter 28 in the 2016 edition of NFPA 1901, the first edition of NFPA 1901 that defined UHP pumps. The technical committee defined UHP pumps as those pumps that have a minimum rated capacity of 6 gpm and that have a rated discharge pressure greater than or equal to 11,00 psi. That’s a rather significant “jump” from 600 to 850 gpm.
Another point of reference regarding UHP technology came with the phase out of halon for aircraft fire suppression in U.S. military services. That phase out prompted military fire services to look for an alternative that could suppress aircraft fires without causing expensive water damage to critical aircraft components.
What does UHP do for fire suppression capability? The pump projects a swirling vortex of exceptionally fine water droplets at a fire. It produces incredibly small water droplets with four times the surface area of water droplets in fire streams produced by conventional low-pressure fire pumps.
As we know from basic fire science classes, the steam conversion is a critical factor in using water for fire suppression. Steam is what takes energy out of a fire while at the same time displacing the oxygen the fire needs to continue burning. With a UHP fire stream, 90% of the water either arrives at the burning fuel or converts to steam.
Extensive testing by the U.S. Air Force found that UHP pumps provided the aircraft fire suppression alternative to halon that the USAF was looking for, as well as an effective fire suppression tool for structural firefighting and Class B fires (e.g., flaming pools of aircraft fuel).
FIRE APPARATUS PUMPS GOING FORWARD
As fire suppression challenges continue to evolve for fire departments of all sizes, the available pump technologies are keeping pace. Fire service leaders looking to specify fire pumps for their fire apparatus will be well-served to look closely at all the available fire pump technologies to find the one that can best meet their community’s fire suppression needs.
