Info

0 5.000 10.000 15,000 20.000 25.000 30.000

TOTAL FLOW (PPH)

0 5.000 10.000 15,000 20.000 25.000 30.000

TOTAL FLOW (PPH)

FIGURE 6 Main boost pump altitude performance (Altitudes are shown on the curves in ft; m = ft X 0.3048; kg/h = PPH X 0.4536; bar = psi X 0.06895; °C = (°F - 32) X 0.556).

flows are very high and the systems are operational for only a small percentage of the mission time, high-speed centrifugal pumps are used in these situations. Centrifugal pumps offer a low unit weight and the ability to be run dry when the system is not operating, thereby conserving power. These centrifugal pumps operate at speeds up to 25,000 rpm and deliver up to 200 gpm (45.42 m3/h at 1000 lb/in2 (69 bar) pressure rise. The fuel actuation function has been provided by variable displacement piston pumps. The fuel boost function for the multiple high-pressure fuel pump engines is usually provided by a single centrifugal boost element either separately mounted on the gearbox or integrated with the main fuel pump.

An alternative drive means has been used for the centrifugal augmentor fuel pump in some applications. An air turbine utilizing engine compressor bleed has been used as a drive source. When the system is non-operational, the pump may be stopped or idled by throttling the turbine inlet air supply, thereby conserving power.

For large engines, such as those used on commercial airlines, the boost stage is a conventional centrifugal element that generally incorporates an axial inducer. For smaller engines used on general aviation and helicopter applications, various specialized centrifugal elements and jet pumps have been used and have shown the capability of meeting the needs of suction feed fuel systems.

As discussed the engine boost pump must function with the airframe boost pump in both the operating and failed, or not operating, conditions. The engine fuel inlet pressure with the airframe boost pumps operational is generally specified over a range from

TABLE 1 Main fuel pump parameter chart

Engine Application and Engine Power

Gear Stage Displacement in3/rev (cm3/rev)

Rated Input Speed RPM

Rated Output Flow GPM

(m3/h)

Rated Pressure Rise lb/in2 (bar)

Unit Weight Pounds

(kg)

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