This question is about the fuel pump controlled by the hydro-mechanical fuel control unit.

  • This is part of a fuel system for a turboprop engine, described on this page which actually comes from a Rolls-Royce book. Full picture for convenience.

I've been staring in vain at this picture for some time, with the hope that something will suddenly become clear:

enter image description here

The pump is supposed to receive low pressure fuel and deliver high pressure fuel at a rate modulated by the FCU using fuel in the purple pipe. The engine speed governor also modulates the pump output.

  • It seems to be a piston pump, pistons being moved in translation by the rotating plate on the left side, but I'm not even sure, and I don't understand how this increases pressure.

  • It seems the governor is not rotating... and I don't get the role of the green governor pressure fuel.

Can you help me understanding how it works?
(I've posted all the details I could gather as an "answer").


1 Answer 1


Sometimes diagrams can be mystifying. This is a video of a variable displacement hydraulic pump of similar principle being torn apart (disassembled would be too gentle a term) by a foul-mouthed Canadian who gives an excellent detailed & clear description of its construction & operation. Language warning for those not used to frontier engineering.

Which will prepare you for this very polite Canadian who shows an actual aircraft fuel pump. (around 7:30)


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