Abstract: An overflow valve is provided in a distributor-type fuel injection pump, for returning excess fuel from the suction chamber of the pump to a lower pressure zone in the pump. The valve comprises a passage communicating with the suction chamber, a check valve arranged within the passage and operable in response to the suction chamber pressure for closing and opening the same passage, and throttle forming means formed by the passage and the check valve. The valve body of the check valve has a pressure-applying surface on which the suction chamber pressure acts in the valve-opening direction, and which assumes a larger surface area when the valve is in an open position than when it is in a closed position. The check valve is closed at the start of the engine to increase the suction chamber pressure so that the timing device of the fuel injection pump acts to advance the fuel injection timing.

Abstract: In a distributor type fuel injection pump for use with an internal combustion engine, which is equipped with an injection timing control device operable in response to oil pressure within a pressure oil chamber, which is variable as a function of the rotational speed of the engine, an overflow valve is provided, which is closed at the start of the engine when the oil pressure within the pressure oil chamber is low, and is opened during subsequent operation of the engine to cause escape of the above oil pressure to a lower pressure zone in the pump, to thereby cause the above injection timing control device to obtain an advance in the fuel injection timing.

Abstract: A diaphragm (38) controls a position of a control sleeve (14) relative to a plunger or piston (16) in response to a pressure differential between a pressure chamber (42) and a control chamber (46) which are defined by the diaphragm (38). The pressure chamber (42) is communicated to an atmospheric pressure or a boost pressure while the control chamber (46) is selectively communicated to a source of vacuum supply through a first check valve (62) and to the atmosphere through a second check valve (58). The first and second check valves open when the pressure inside the control chamber is higher and lower than a reference level, respectively, thereby maintaining the pressure within the control chamber (46) substantially at the reference level to promote an accurate control of the control sleeve (14).