FUEL PUMP

PURPOSE:To sufficiently lower pressure within a pump chamber when fuel is taken in so as to enhance the air intake performance of a fuel pump by setting the blocking force for the delivery valve seat of a delivery valve communicated with a pump chamber larger than that for the air intake valve seat of an air intake valve. CONSTITUTION:When an engine is operated pulsating pressure generated in the engine is introduced into a pressure receiving chamber G via an introducing passage 4; when e.g. the negative pressure force of the pulsating pressure acts on the pressure receiving chamber G a partition body 3 moves toward the pressure receiving chamber G to increase the capacity of the inside of a pump chamber P. A delivery valve seat 8 is blocked with a relatively large blocking force by a delivery valve 9 and leakage does not occur from the delivery valve seat 8 to inside the pump chamber P and so pressure within the pump chamber P is sufficiently lowered. Because an air intake valve seat 5 is blocked with a blocking force smaller than the above blocking force by an air intake valve 6, the air intake valve seat 5 is surely opened by means of pressure within the pump chamber P which is sufficiently lowered. Thus fuel contained in a fuel source T is surely taken into the pump chamber P.