BY DOUGLAS PIETZ
Apparatus with fire pumps are not unique concepts in the fire service; rather, they are the cornerstone of every department.
Hours are spent on the bells and whistles of new apparatus, whether to purchase an aerial platform rather than a straight stick, and even if a rescue-pumper is the best option for a department. Yet, the biggest part of a pumper is often overlooked, or at least proper attention is not placed on the most important component of the engine—the fire pump.
Pump Theory
In pumper operator class, the hardest lecture to swallow is pump theory. True pump theory has complex formulas and equations to determine maximum capabilities of pumps under various conditions. Unless you are a math geek, most of the fire service is lost at the word formula. We take a complex component of the apparatus and bring everything down to the easiest of ways to interpret complex formulas and develop pump charts. These charts are the backbone to rapid response; they get the operator very close to the actual pressures needed. Soon the formulas are forgotten, and the operator is reliant on a chart and, as a result, the theory of the pump is gone too.
So, what this relates to is sending drivers or officers who are not up on pump capabilities to a prebuild for an engine. As a result, departments are forced to rely on the manufacturer’s build team for advice or recommendations. Thus, larger pumps are put into apparatus, and larger pumps need larger motors to drive them. All of this leads to a larger price tag.
The better choice is to look at the needs of the department and community. What fire loads are present in the district? What are the water demands to meet those needs? What water tower operations or large lines need to be supported? Do you have high-rise buildings? Do you operate a water tower with dual nozzles at the bucket? What flows are your hydrants capable of producing? Do you use a water shuttle operation? Answering these questions will help in the process, which is much like homework. My department operates a 2,250-gallon-per-minute (gpm) pump that is rated at 1,500 gpm. The capability of the pump is a combination of the pump and engine needed to drive the pump. It meets our needs to supply greater than 2,000 gpm from a hydrant to be able to use both nozzles on an aerial platform and also feeds the needs of the downtown high-rise district. The pump is Underwriters Laboratories-derated to ensure that the it will pass pump tests. If we rated our pumps at 2,250, then any decrease in engine or pump performance would yield an apparatus that failed a pump test—and that means being out of service.
None of these questions seem to have anything to do with pump theory. But, I would argue that they have everything to do with it. Do the ratings on your new pumper meet the needs of the community, or are you purchasing the engine that you had because it was adequate? What are the future developments in your area, and are you purchasing an apparatus that is good today but not 15 or 20 years from now when the apparatus is in reserve status?
Pressure or Volume
Generally, with fire pumps, there is a choice of pressure or volume. The lower the pressure on the pump, the more volume can be pushed. The higher the pressure on the pump, the less volume can be pushed. This seems to be a simple concept until an engineer is in a situation where more water is needed. The reaction almost all the time is to throttle up and give more pressure. But, with more pr