Vehicle-mounted air compressor and bottle cap assembly

An air compressor, comprising:

• an air compressor main body;
• and
• a bottle cap assembly, comprising:
• a bottle cap component, installed on the air compressor main body and has an air inlet end and an air outlet end connected to each other, wherein the bottle cap component is inserted into the air compressor main body through the air inlet end along an inserting direction, which is the same as an air inlet direction of the air inlet, an air flow from the air compressor main body is adapted to pass through the air inlet end and the air outlet end in sequence, and the bottle cap component has at least one assembling hole;
• and
• at least one fastening component, passing through the at least one assembling hole along a fastening direction to fasten the bottle cap component to the air compressor main body, wherein the fastening direction is the same as the inserting direction.