PUMP

1 . A fuel pumping unit for an aero-engine, the unit having a low pressure pump and a high pressure pump, the low pressure pump supplying fuel at a raised pressure to the high pressure pump for onward supply to a fuel metering unit of the engine, wherein the low pressure pump has:

a brushless electrical motor including a stator assembly and a rotor ring arranged externally of the stator assembly; and

a centrifugal impeller operatively connected to the rotor ring such that the electrical motor rotates the impeller, the impeller being configured to raise the pressure of a fluid which flows through the impeller between an inlet and an outlet thereof;

wherein the low pressure pump is configured such that a portion of the raised pressure fluid flow is diverted to form a recirculation flow which circulates through and cools the electrical motor before being returned to the impeller for re-pressurisation thereby.

2 . A fuel pumping unit according to claim 1 , wherein the centrifugal impeller is coaxial with the motor.

3 . A fuel pumping unit according to claim 1 , wherein the electrical motor is fully immersed in the pumped fluid.

4 . A fuel pumping unit according to claim 1 , wherein the centrifugal impeller has an inducer section which extends from an inlet for the fluid flow towards an outlet for the fluid flow.

5 . A fuel pumping unit according to claim 4 , wherein the centrifugal impeller further has an exducer section located in flow series between the inducer section and the outlet.

6 . A fuel pumping unit according to claim 1 , wherein the rotor ring is located within the centrifugal impeller such that the raised pressure fluid flow passes radially outwardly of the rotor ring towards the outlet.

7 . An aero-engine having a fuel pumping unit according to claim 1 .