Roots pump

A Roots pump comprising:

• a rotary shaft that is rotated by a drive source;
• a drive rotor that is driven by the rotary shaft;
• a driven rotor that is driven in association with the drive rotor;
• a housing unit that includes:
• a rotor housing that accommodates the drive rotor and the driven rotor, the rotor housing including an end wall, through which the rotary shaft extends, and a peripheral wall, which extends from an outer periphery of the end wall;
• and
• a cover member, which closes an opening of the rotor housing;
• and
• a seal member, which is arranged between the rotor housing and the cover member, wherein
• the peripheral wall includes a mating surface that faces the cover member,
• the cover member includes a mating surface that faces the peripheral wall,
• at least one of the mating surfaces includes an annular first groove,
• the first groove includes a side surface on a radially inner side and a side surface on a radially outer side, the side surfaces facing each other,
• the seal member is accommodated in the first groove,
• the rotor housing includes a bulging portion, which is a part of the peripheral wall that bulges radially inward at a position between the drive rotor and the driven rotor,
• the bulging portion includes:
• a mating surface that faces the cover member;
• and
• a second groove, which is connected to the side surface on the radially inner side of the first groove,
• the seal member includes:
• an annular seal body;
• first projections, which project from the seal body toward one of the side surface on the radially inner side or the side surface on the radially outer side of the first groove, the first projections being arranged at intervals in a circumferential direction of the seal body;
• and
• a second projection, which projects further radially inward from the seal body than the first projections,
• each first projection includes a distal end that contacts one of the side surface on the radially inner side or the side surface on the radially outer side of the first groove, and
• the second projection is arranged in the second groove so as to determine a position of the seal body in the first groove.