Pumping Arrangement
An aircraft fuel pumping arrangement comprises a first fuel pump, an electrically powered motor operable to drive the first fuel pump to deliver fuel to an outlet, a second fuel pump, a gas driven turbine operable to drive the second fuel pump to deliver fuel to the outlet, and a controller operable to control the operation of the gas driven turbine to determine the rate at which the second fuel pump is driven.
1 . An aircraft fuel pumping arrangement comprising a first fuel pump, an electrically powered motor operable to drive the first fuel pump to deliver fuel to an outlet, a second fuel pump, a gas driven turbine operable to drive the second fuel pump to deliver fuel to the outlet, and a controller operable to control the operation of the gas driven turbine to determine the rate at which the second fuel pump is driven, wherein the first and second fuel pumps are arranged to be used in combination during high engine load conditions to meet the fuel delivery and system pressure level requirements of the engine, the output of the electrically powered motor driven first fuel pump, alone, normally being used to achieve the required fuel delivery and system pressure level in lower engine load conditions.
2 . An arrangement according to claim 1 , wherein the controller comprises a gas valve operable to control and/or modulate the supply of gas to the turbine and thereby control operation of the gas driven turbine during all engine operating conditions.
3 . An arrangement according to claim 1 , wherein the first and second fuel pumps are arranged in parallel with one another.
4 . An arrangement according to claim 3 , wherein the second fuel pump comprises a positive displacement pump.
5 . An arrangement according to claim 3 , further comprising a dedicated fuel valve located adjacent the first fuel pump and operable to prevent fuel delivered from the second fuel pump from returning through the first fuel pump to a low pressure side thereof.
6 . An arrangement according to claim 5 , wherein the dedicated fuel valve comprises a non-return valve.
7 . An arrangement according to claim 1 , wherein the first and second pumps are arranged in series.
8 . An arrangement according to claim 7 , wherein the second pump is located downstream of the first pump.
9 . An arrangement according to claim 7 , wherein the second fuel pump is arranged, during periods of high engine load conditions, to raise the pressure from which fuel is supplied from the first pump to the required system pressure level and thereby assist the electrically powered motor driven first fuel pump in achieving the desired fuel delivery and system pressure level.
10 . An arrangement according to claim 7 , wherein the second fuel pump comprises a roto-dynamic pump so as to allow the delivery of fuel from the first fuel pump in a relatively unimpeded manner when the turbine and second fuel pump are inactive.
11 . An arrangement according to claim 10 , wherein the roto-dynamic pump is a centrifugal pump.
12 . An arrangement according to claim 7 , and further comprising a by-pass passage around the first fuel pump, a dedicated fuel valve being provided in the by-pass passage.
13 . An arrangement according to claim 12 , wherein the dedicated fuel valve comprises one of a non-return valve and a by-pass valve.