Aircraft Fuel Booster Pump - Centrifugal & Immersed in Fuel

[mrajkumar]

What is the correct way to put limitation on different aircraft flying conditions with respect to the cavitation point of view of the Fuel booster pump in the aircraft? The pump is immersed in the fuel and the fuel tank is vented to atmosphere(in atmospheric pressure, which will change with altitude)

From my understanding, as the flow rate increases the minimum pressure required at the suction side of the pump to avoid cavitation will increase. So, To specify the limitation like, "the maximum possible flow rate for a particular altitude will be fixed" is it correct?. Here I've taken only the atmospheric pressure exerted on the fuel surface, irrespective of the fuel column available above the inlet of the pump (since the fuel column level will vary according the consumption rate), or do we have to specify the limitation in terms of, "for particular fuel column available, the maximum flow rate possible will be fixed(taking the pressure because of fuel head also)".

Out of two approach which is the correct way to put limitation on flying conditions!

*(the fuel column measured is by gauging probe which is not exact always )

 

[nucleus]

From FAR Part 25.955:
(a) Each fuel system must provide at least 100 percent of the fuel flow required under each intended operating condition and maneuver. Compliance must be shown as follows:
(1) Fuel must be delivered to each engine at a pressure within the limits specified in the engine type certificate.
(2) The quantity of fuel in the tank may not exceed the amount established as the unusable fuel supply for that tank under the requirements of §25.959 plus that necessary to show compliance with this section.
(3) Each main pump must be used that is necessary for each operating condition and attitude for which compliance with this section is shown, and the appropriate emergency pump must be substituted for each main pump so used.
Basically, what they are saying is the boost pump, if it is required to be operated, must provide full flow until the tank is empty. Besides the boost pump there is another pump on the engine and that is called the main pump in the regulations.

Here is a link to the regulations:

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=8f2d082611715d23af524fed5ec3b5cf&rgn=div8&view=text&node=14:1.0.1.3.11.5.184.19&idno=14

To see how manufactures have designed their systems go to My Aircraft at this link and select type and fuel system:

http://www.smartcockpit.com/