Fuel injection apparatus for diesel engines includes an injection pump connected to an injector nozzle through a control device constituted by two calibrated and opposed non-return valves arranged to keep a residual pressure of a predetermined magnitude in the fuel supply passage to the injector between each injection cycle and the next. The two non-return valves are located downstream of the output of the pump and are preferably inserted in a body fixed to or forming part of the injector, or forming part of the delivery union of the pump.

A check valve includes an outer valve body and an inner poppet valve moveable relative to the valve body and spring-biased into a closed position. The inner poppet valve has first and second stage openings. The first stage preferably has a single, relatively small through-hole into the chamber of the poppet valve, while the second stage preferably has multiple openings of a larger diameter. The first and second stage openings are spaced axially along the poppet valve, with the first stage opening being located closer to the valve head of the poppet valve than the second stage openings. In the closed position, fluid flow is blocked through both the first and second stage openings. When the cracking force of the valve is exceeded and the valve head moves away from the valve seat, fill flow occurs through the first stage opening and is restricted through the second stage openings. The restricted fluid flow causes the pressure drop across the check valve to be satisfactory at low flow rates to cause the poppet valve to stroke long enough such that particles will pass easily between the valve head and the valve seat. The flow increases through the second stage openings as the poppet valve moves toward its open position. The pressure drop is minimized at high flow rates to maximize the efficiency of the check valve. The check valve also has relatively few parts, and can be easily assembled and installed within the housing of a fuel nozzle.