Marc-Antoine
TreeHouser
The flat spot acts as a rotating valve to close/open the intake and outpout holes of the pump's cylinder. Somewhere on the small shaft a ramp/came makes the shaft moves axially while it's rotating. The both combined give the pumping motion. No check valve, very simple system.
It looks like the ramp on your pump is molded on the plastic gear: the rounded groove on the left of the flutes. In the Stihl's, the end of the shaft is machined. It isn't much of a slope, but with the huge number of rotations, it gives a substantial amount of oil.
It looks like the ramp on your pump is molded on the plastic gear: the rounded groove on the left of the flutes. In the Stihl's, the end of the shaft is machined. It isn't much of a slope, but with the huge number of rotations, it gives a substantial amount of oil.