When fire departments think of pump performance, they usually focus on the flow and pressure ratings stamped on the pump plate. That’s only part of the story. To fully understand what a pump can do, you need to be aware of several other factors that determine performance.

NFPA ratings. The rated pump performance is defined by NFPA standards. Structural and industrial apparatus are covered by NFPA 1901, which specifies three specific discharge flows and pressures that must be met: 100% of rated flow at 150 psi, 70% at 200 psi and 50% at 250 psi. Wildland apparatus are covered by NFPA 1906, which allows a broader range of flows and pressures that can be significantly less than those required by NFPA 1901. The Insurance Services Office uses the NFPA 1901 ratings, and departments may get little or no ISO credit for some wildland pumpers.

Pump curves. The rated performance only covers specific points of operation. To understand how a pump will perform at other flows or pressures, departments need to consult the manufacturer to review the entire pump curve. For example, if a department wishes to run a single-stage centrifugal pump at pressures above 250 psi, they would need to review the pump curve to see if that is possible. With many pumps, the performance falls off dramatically at very high pressures and very low flows.

Power and Speed. Pump curves also show the required power and pump speed for the entire operating range. For pumps driven off midship gear boxes or power take-offs, both the power and speed are determined by the vehicle engine and the drive gear ratios. In some cases, departments may have to specify more powerful engines or adjust the drive gear ratios in order to get desired performance. This is something the manufacturer should calculate based on input from the customer.

Efficiency and thermal capacity. Pump efficiency varies with the pump speed. Most pumps are designed to operate most efficiently at speeds near the rated flow and pressure. At the extreme ends of the curve, pumps operate very inefficiently and waste power. This commonly occurs when large pumps are made to run at very low speeds. To compound the problem, when these pumps run at low speeds for extended periods, the water temperatures can increase to dangerous levels and potentially cause cavitation and pump damage.

Elevation. The NFPA ratings apply to pumps operating at elevations from sea level to 2,000 feet. Above that, departments need to specify the desired pump ratings and elevation so the manufacturer can make appropriate changes to the pump configuration at the time of construction. The manufacturer may also have to make changes to the engine to compensate for operation at higher elevations. This is not something that can be adjusted after the apparatus is delivered.

Water sources. The NFPA standards specify that pump ratings must be determined while drafting from unpressurized water sources. The standards also define the elevation of the terrain, diameter and length of suction hose, height of lift, atmospheric pressure and water temperature. Departments that draft under different conditions or that take water from pressurized sources will find that pump performance varies greatly.

Annual pump tests. Over time, pumps wear, engines lose power and other factors may change. That’s why NFPA 1911, as well as the ISO rating schedule, requires annual tests to ensure that pumps still can perform to the same level as when they first went in service. Follow the procedures and record the results if you want credit.

Understanding pump performance is not as simple as reading the pump panel data plate. Departments need to be aware of the many factors that determine performance — both when the pump is first specified and after it has been in service. Understanding these factors can help you get maximum performance and avoid a lot of problems.