Aircraft engine fuel system

An aircraft engine fuel system, comprising:

• a metering valve having inlet and outlet sides to control fuel flow from the inlet to the outlet side;
• main and auxiliary pumps to pump first and second fuel along separate fuel lines toward the inlet side, respectively;
• a pressure regulating valve (PRV) operably disposed between the main pump and the inlet side to restrict the first fuel flow in accordance with a pressure differential between the outlet side and second fuel pressure and to force a portion of the first fuel into a bypass condition;
• a check valve, coupled to the pressure regulating valve, which, when closed restricts a flow of the bypassed portion of the first fuel toward the auxiliary pump;
• and
• an ejector pump, operably disposed between the check valve and the auxiliary pump,
• which, when the check valve is closed, pumps second fuel from the pressure regulating valve toward the auxiliary pump,
• wherein the PRV comprises:
• first and second connected piston heads elastically anchored to a first valve end and biased toward a second valve end,
• the second piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the auxiliary pump is bypassed from the inlet side with the first and second piston heads moved toward the first valve end by a first distance from the second valve end, and
• the first piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the main pump is bypassed from the inlet side with the first and second piston heads only moved toward the first valve end by a second distance from the second valve end, which is larger than the first distance.

An aircraft engine fuel system, comprising:

• a first valve to control fuel flow;
• first and second pumps to pump fuel toward the first valve;
• second and third valves to regulate an amount of fuel permitted to be pumped to an inlet side of the first valve, the second valve comprising first and second connected piston heads elastically anchored to a first valve end and biased toward a second valve end, the second piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the second pump is bypassed from the inlet side with the first and second piston heads moved toward the first valve end by a first distance from the second valve end, and the first piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the first pump is bypassed from the inlet side with the first and second piston heads only moved toward the first valve end by a second distance from the second valve end, which is larger than the first distance;
• and
• a third pump operably disposed between the third valve and the second pump to pump a portion of fuel toward the second pump, wherein the second valve is configured:
• with the grooves non-communicative with the conduits during start conditions such that substantially all of the fuel pumped by the first and second pumps is permitted to be pumped to the first valve,
• with the groove of the second piston head fluidly communicative with the conduit by which excess fuel pumped by the second pump is bypassed from the inlet side during climb conditions such that substantially all of the fuel pumped by the first pump is permitted to be pumped to the first valve and excess fuel pumped by the second pump is bypassed between a valve wall and the second piston head to the third pump, and
• with the groove of the first piston head fluidly communicative with the conduit by which excess fuel pumped by the first pump is bypassed from the inlet side during idle conditions such that substantially all of the fuel pumped by the second pump is bypassed between the valve wall and the second piston head to the third pump and excess fuel pumped by the first pump is bypassed between the valve wall and the first grooved piston head to the first pump.