An object is to suppress cavitation generated at a distal end portion of a seat face when a valve body and a seat portion collide with each other. In a relief valve of a fuel pump, an intersection between the seat face and a flow channel hole is formed at a position more distant than the seat portion formed of the valve body in a valve closing state and the seat face in order to suppress generation of cavitation bubbles when the valve body improves and releases high-pressure fuel.

A pressurized fuel system for an engine includes a fuel pump in a pump protection device structured to drain pressurized fuel from a common rail to provide fuel flow through the fuel pump that limits cavitation. The device includes a valve mechanism having a first valve and a second valve that are movable to an open position and a closed position respectively, in response to valve opening and valve closing rail pressures. The active pressure range of the device may be a medium pressure range.

A method and apparatus for determining a characteristic of an injector are set forth. In one example, a compressed gas is applied to the inlet chamber of the injector while the spoolvalve is closed until the pressure of the compressed gas in the inlet chamber reaches a predetermined pressure. A change in pressure of the compressed gas in the inlet chamber is measured over time while the spool valve is closed. The pressure change measurement corresponds to the characteristic of the injector that is to be determined.