Positive displacement vacuum pump having a piston actuated by an alternative linear movement

Positive displacement vacuum pump, comprising:

• a pump body;
• a piston positioned in said pump body and comprising a longitudinal axis and a first end, said piston being mounted for actuation by alternative linear movement;
• an elastic element biasing said piston in a first direction;
• a cam acting on said first end of said piston, said cam being rotatably movable along an axis that is coaxial with said longitudinal axis of said piston to drive said piston in an alternating linear movement;
• and
• a transverse bar positioned between said first end of said piston and said cam, said transverse bar comprising a length and being rotationally fixed but translationally guided in the direction of alternative linear movement of said piston;
• said cam comprising a double surface to equally bias said transverse bar at two positions along the length of the bar.