The Ideal Engine, Defined
We've all heard the phrase, “It isn't the size of the dog in the fight; it's the size of the fight in the dog.” The same can be said of wildland fire engines. Although the National Wildland Coordinating Group has identified seven separate engine types, none fills all needs.
Although each type can fulfill several roles, the only engine type that can reasonably fill all needs is the Type 3. Unfortunately, most of these are pretty large — in some cases, their size can limit their versatility in many wildland firefighting scenarios. These larger units might find it hard to travel in tight places, as well as along some dozer lines and hand-constructed fire lines.
From this view the Darley HE 64 pump is visible, as is the rear reel, drip torch on the left and hose fittings slide-out tray. Note the lift created by the extra leaves in the rear as well as the full length underbed compartment.
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Given these limitations, I decided to design and build a Type 3 engine that would meet the NWCG's criteria for both Types 3 and 6 nearly two years ago. The engine needed to be able to go just about anywhere an engine might be needed, much like the typical Type 6 truck. It needed to pump two or three 1½-inch hand lines in order to perform structure protection. Accordingly, the engine had to be able to flow 250-400gpm. It also needed to be able to draft at a higher volume and connect to a hydrant using a 2½-inch or larger supply line. In addition to the usual Type 3 hose load, it needed to carry 500 feet or more of this 2½-inch hose. Also, it had to carry 500 gallons of water and 10 to 20 gallons of Class A foam.
My vision was to design and build this truck on a typical 17,950 to 19,000 GVWR all-wheel-drive chassis. The challenge was to get 500 gallons of water, 10 or more gallons of Class A foam and a pump meeting Type 3 requirements (150gpm at 250psi) onto a smaller chassis without exceeding the vehicle's GVWR.
The basic fire body had to be built using aluminum to maximize the available GVWR by reducing the overall weight compared to a steel body of the same design. The weight of the water and tank are constants, as is the curb weight of the truck itself. The hope was that, by building the body out of aluminum, the weight of the fire body might be cut in half.
The next challenge was to find a portable pump capable of 150gpm at 250psi. Yeah, sure! All the Type 3s I've seen are equipped with mid-ship mounted pumps that weigh a lot and are driven by the chassis engine. The weight of these pumps pretty well killed the idea. So began my research of pump manufacturers' lists of engine-driven or portable pumps. Nearly every pump manufacturer can provide a pump that meets the requirements of a Type 3, but all come with weight — the dreaded weight that kills the idea. I found many pumps that “almost” did the job, but none that could do the job was small enough and light enough.
My research continued. It's hard to recall how many people I consulted. Some were experts in their field, and some were seasoned wildland firefighters. Connecting two separate pumps into a single discharge manifold to obtain both the pressure and volume was considered, but the overall size and awkwardness of the arrangement made it impractical. Many of these people suggested using the smallest pump that almost met the criteria. Doing so would effectively “dodge” the specification, so it was not considered.
After what seemed like an endless search, the Darley HE 64 RS pump was discovered, almost as an afterthought. The picture in the catalog looked a little questionable, but the performance curve clearly showed that this pump could do the job.
The Darley HE 64 RS pump is driven by a gasoline-powered, two-cycle Rotax aircraft engine. This small engine is loud, but it weighs only 275 pounds and meets the pumping requirements. Because I'm not a trained mechanic, I asked our professional fire apparatus mechanics for their opinion. They offered two completely different views, plus some weird looks. We took a calculated risk and bought two of these pumps.
Custom aluminum bodies were designed specifically for these trucks. We added a foam-proportioning injection system and engineered things as we went along. The chassis was a new 2008 Ford F-550 4×4 with diesel engine and automatic transmission. We added four rear leaf springs, not to increase the GVWR but to better support the constant weight of 500 gallons of water. We also added a 3-inch spacer pad inside the front springs. The combination of these provided a 3-inch lifted look to the truck. We changed out the standard tires with slightly larger and more puncture-resistant tires, which also added to the lifted look.
During the 2009 fire season, these trucks were driven to several small local fires, two larger out-of-area wildfires and a prescribed burn. They performed exactly as we had hoped. They made it up and down dozer lines while carrying 500 gallons, they climbed steep hills with less than a full tank of water, and they pumped and drafted as planned. Unofficial pump tests at an altitude of 5,400 feet demonstrated they can easily pump 250gpm from the tank at 120psi, and they pumped 401gpm at 60psi from draft. They also pumped 150gpm at 230psi. Darley thought this would be the maximum pressure possible at this altitude. Plus, the HE 64 RS pumps don't seem much louder than other portable pumps (available from several manufacturers) when throttled up to achieve maximum performance.
Fully loaded, including a spare tire and 800 feet of single-jacket, lightweight, 2½-inch hose and staffed with three firefighters, the trucks weighed in at 17,500 pounds — cutting the maximum GVWR pretty close. Ford and Dodge both offer chassis options with a GVWR of 19,000 pounds, so using this greater rating offered some wiggle room.
The inherent advantage of these trucks is: They are nearly the size of a typical Type 6, yet have the punch of a Type 3 and maybe even a Type 2 structure engine. They have the maneuverability of a Type 6 but the water of a Type 3. They can pump a long hose lay, and have the pump capacity to supply two or three 1½-inch hand lines when doing structure protection or structure attack in a wildland urban interface. Also, they can pump a 2½-inch supply line from draft at a water source or hydrant with enough pressure to serve as a small master stream.
The bottom line is that these trucks are versatile. Their smaller size enables greater maneuverability, and yet they have a larger firefighting capacity.
Larry Marcum is chief of the San Juan County Fire Department of Aztec, New Mexico. A 30-year firefighting veteran, Marcum is both a task force leader and the strike team leader — engines.
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