| 摘要 |
A fuel pumping unit has a low pressure centrifugal pump (42) and a high pressure centrifugal pump (44). In use, the low pressure pump supplies fuel at a boosted pressure to the high pressure pump for onward supply to a fuel metering unit (FMU). The pumping unit further has a drive input (30) which drives the low and high pressure pumps. A gear arrangement (32,34,36) is operatively located between the drive input and the low and high pressure pumps such that the low and high pressure pumps are driven at different speeds by the drive input. Further, a selector valve (46) is provided to select between a high pressure mode where both pumps (42,44) are connected in series or a low pressure mode where only the low pressure pump (42) provides fuel to FMU. Further, a positive displacement pump (60) is foreseen for a start-up mode. |
