THE EVOLUTION OF THE MINI-PUMPER

BY PAUL B. CROMER

It has been nearly 23 years since the City of Buffalo showed how useful a fleet of mini-pumpers could be in times of severe weather. How has the mini evolved since then, and which departments use it?

WHAT IS A MINI-PUMPER?
For purposes of this discussion, a mini-pumper is a fire apparatus based on a commercial light-truck cab and chassis with a Gross Vehicle Weight Rating (GVWR) of 10,000 pounds or greater. Such a pumper falls under the classification of “Initial Attack Apparatus” in National Fire Protection Association (NFPA) Standard 1901, Standard for Automotive Fire Apparatus.

A typical mini-pumper, this apparatus is based on a Ford Super Duty 2 2 2 cab and chassis. Major features include 250-gpm pumping capacity, 1½- and 3-inch hose, a booster reel, and a 250-gallon tank. (Photo courtesy of W.S. Darley & Co.)

Note: Although various requirements from NFPA 1901 are presented in this article, you must consult the standard for design criteria and equipment requirements.

Compared with conventional pumpers, a mini-pumper’s power plant is limited to those engines designed for light trucks. A mini-pumper body has limited storage space and generally carries no more than about 200 to 300 gallons of water.

APPLICATIONS
Mini-pumpers have many applications in the modern fire department’s arsenal of apparatus. They include the following:

• Residential first-in apparatus. Mini-pumpers are small and can maneuver easily in residential areas; they can access most driveways or backyards. For example, a mini-pumper might be able to go in the backyard of a house with a swimming pool, draft from the pool, and relay to other apparatus in the case of a major fire in a residential area.
• Industrial fire brigades. Mini-pumpers can go places where normal-size pumpers— because of their weight or size—cannot go in industrial plants.
• Brush fires in rugged country. Four-wheel-drive mini-pumpers are lighter and more maneuverable than full-size equipment.

GROSS VEHICLE WEIGHT RATING
The GVWR is the manufacturer’s specified maximum load- carrying capacity for the vehicle; this includes the cab and chassis, the body, the pump, the water, fuel, passengers, and all equipment carried on the pumper —everything. It is the limit to which the vehicle can be loaded and still operate safely. The body builder must observe this maximum while designing and building the pumper, and the customer must observe this limit when outfitting and operating it. It is easy to overload a mini-pumper. The temptation to add just one more piece of equipment is always there.

MAJOR EQUIPMENT
Custom fire apparatus/body manufacturers build most mini-pumpers on a light truck cab and chassis provided by one of the major automobile companies. The builder installs the body and the pump and piping and tests the unit. It may also install the outfitting items and deliver the apparatus to the customer.

Cab and ChassisAs an example, a cab and chassis frequently used for mini-pumpers is the Ford F-350 Super Duty. This unit can be equipped with axles, suspensions, and dual rear wheels for a GVWR of 11,200 pounds. This includes a standard cab with one bench-type seat. Other models by the same maker have a range of GVWRs up to 19,000 pounds with a standard cab. It pays to thoroughly investigate how choices in equipment (transmissions, four-wheel drive, tires and wheels, suspensions, and so on) and accessories can affect the GVWR of the cab and chassis you select.

Power Train
The power train used in the cab and chassis is important because it determines the maximum power available for driving the pump. Factors that will determine power train choices include whether the pump is to be driven by the vehicle’s engine using a power-takeoff (PTO) on the transmission and whether it is to operate in pump-and-roll scenarios.

Engine
The engine must be powerful enough to handle the maximum pump power required for at least an hour. In addition, the cooling system should be rated to allow the engine to operate at maximum pumping power without overheating while the vehicle is stationary. Also, if a front-mounted pump is desired, determine its power demand early in the selection process to be sure that the front of the engine crankshaft can transmit sufficient power to drive the pump.

The engine can be spark-ignition or diesel. Diesel engines are common for trucks in the 10,000-pound-and-higher GVWR range; they eliminate the fire and reliability problems associated with gasoline engines and provide relatively good fuel endurance. Diesels are high-torque engines and require transmissions and other driveline components that are matched to their torque and torsional vibration characteristics.

Transmission
The type of transmission selected determines how the fire pump is driven. Some transmissions can be equipped with a PTO for driving the pump. If a PTO is not available on the selected transmission, the pump must be midship-driven, front-driven, or powered by a separate engine. In some cases, transmission oil coolers may be required to keep the transmission—and PTO—cool during extended pumping operations. NFPA 1901 requires that the power train components, from the engine to the pump, be capable of handling the power required by the pump during the 50-minute pump test.

The transmission arrangement and transfer case, where the truck is four-wheel drive, plus other drivetrain components beneath the truck frame also affect the selection of the pump and pump drive. In some cases, there may not be enough room for a midship- or PTO-driven pump, and a separate engine or front-driven pump must be used.

Dual Rear Wheels
Cab and chassis in the 10,000-pound-and-above GVWR range usually have dual rear wheels. Consider the overall body width, needed for this arrangement when determining the suitability of the apparatus size for a given job or limited accessibility hazard, such as the manufacturing floor of an industrial plant.

Pump
Pump capacities for mini-pumpers generally run from 250 gpm to about 500 gpm. Where high pressures—up to 800 psi—are required, multistage centrifugal pumps or reciprocating pumps are available. If a separate special-purpose transmission is required to drive the pump, include it as part of the pump size and weight when laying out the architecture of the apparatus.

Outfitting Items
Tables 1, 2, and 3 show quantities and weights for NFPA 1901-required and -recommended outfitting itemsYou may want to specify additional equipment such as mast-type lights, monitors, and foam systems.

CONSIDERATIONS FOR PURCHASERS
Mini-pumpers are small; therefore, design them carefully to get the most out of their resources. Three major mini-pumper design and specification considerations are mission/support requirement, powering the pump, and weight and weight distribution.

• The mission/support requirement for the mini-pumper—the size and type of fires the pumper is expected to handle and how to get sufficient personnel to the scene to use the pumper to its full capability—must be well-defined.
• Define pump power requirements early in the design so adequate power train components can be chosen without overloading.
• Mini-pumpers are light vehicles. For safe and efficient operation, you must closely monitor equipment, placement of stored items, and changes in weights and the areas in which the weight is carried.
• Note: An appendix illustrating some simple methods for sizing a mini-pumper, determining the power required to drive its pump, and calculating its axle loads is available at cromer@csiway.com

PAUL B. CROMER is a designer and technical writer in the ship design and mechanical equipment design fields. He lives and works in Southern California.