Lubricant injector with improved piston

A lubricant injector for delivering a predetermined quantity of lubricant, the injector comprising:

• a body having opposing first and second ends and a longitudinal axis extending generally between the two ends, the body including an inlet at the first end fluidly coupleable to a source of lubricant, an outlet, a delivery chamber fluidly coupled with the outlet and an elongated bore spaced axially from the body inlet and having a first port fluidly connected with the body inlet and a second port disposed axially between the body inlet and the first port and fluidly connected with the delivery chamber, the bore being defined by a substantially circular cylindrical inner circumferential surface having an inside diameter, the inside diameter having a substantially constant value along the axis;
• and
• a piston disposed within the elongated bore so as to divide the bore into an operating chamber fluidly coupled with the first port and a measuring chamber fluidly coupled with the second port, the measuring chamber being located axially between the operating chamber and the body first end, the piston including a generally circular cylindrical body having opposing first and second axial ends and an outer surface and an outer circumferential surface extending axially between the ends and slidably disposed against the bore inner surface, the outer surface having an outside diameter that is generally constant along the axis between the first and second ends;
• and
• a rod connected with the piston so as to extend generally axially away from the piston second axial end and through the operating chamber section, the rod having an outside diameter;
• and
• wherein the piston has a first, substantially circular radial pressure surface on the first axial end, the first pressure surface partially bounding the measuring chamber and having a first surface area, and a second, generally annular radial pressure surface on the second axial end defined between the rod outer perimeter and the piston outer perimeter, the second pressure surface partially bounding the operating chamber and having a second surface area, the piston being axially displaceable solely by a differential between a first force generated by lubricant pressure exerted on the first pressure surface and a second force generated by lubricant pressure exerted on the second pressure surface.