High pressure pump

A high pressure pump of a common rail pump system, the high pressure pump comprising:

• a pump body having a cylinder with a piston bore,
• a piston reciprocally driven in the piston bore to pressurize fuel in the cylinder,
• a leakage gap between an outer surface of the piston and an inner surface of the piston bore,
• a bellow having a first end secured to the pump body concentric with the piston bore and a second end secured to the piston remote from the pump body, and defining a bellow internal volume within the bellow,
• a back leak connection at the bellow, connected to a drainage line for draining leakage fuel off an interior space of the bellow and delivering it to a fuel supply line coming from a fuel tank, and
• a recess extending from the drainage line hydraulically connected to the piston bore so that fuel flowing through the drainage line applies a suction to such that fuel leaking in a clearance between the piston and the piston bore is sucked into the drainage line directly through the recess before it enters the bellow,
• wherein the bellow internal volume is communicatively coupled to both (a) the leakage gap between the outer surface of the piston and the inner surface of the piston bore and (b) the drainage line,
• wherein the bellow is coupled to the piston at the second end such that a reciprocal movement of the piston causes a corresponding reciprocal change in the bellow internal volume, and
• wherein during the reciprocal movement of the piston, fuel leaks through the leakage gap and into the bellow internal volume, and said fuel subsequently pumped from the bellow internal volume into the drainage line due to the reciprocal change in the bellow internal volume.