A hydraulic system, such as a fuel injection system, includes a fixed displacement
pump with at least one pump piston. A sleeve surrounds each pump piston and provides
the method by which fluid displaced by the pumping stroke of the pump piston is
directed either to a high pressure area in the pump or a low pressure area. The
sleeves are a portion of an electro-hydraulic controller that includes a mechanical
bias to bias the pump to a high output position when a pressure differential between
the outlet area and the inlet area is relatively low, such as at cold start up.
This aspect facilitates priming of the system. In addition, the controller includes
a biasing hydraulic surface in opposition to the mechanical biaser that serves
to bias the pump to its low output position when the pressure differential between
the outlet area and the inlet area is relatively high. This aspect prevents over
pressurization in the event that electric current to the controller is disrupted.
