Air pump

An air pump comprising:

• a main frame having a front end and a rear end;
• a first pressure cylinder movably mounted in the main frame;
• a second pressure cylinder movably mounted in the main frame and being parallel with the first pressure cylinder at an interval;
• an outlet device connected to and communicating with the pressure cylinders near the front end of the main frame and having
• two side faces;
• and
• a check valve mounted in the outlet device near the first pressure cylinder:
• a footboard pivotally connected to the main frame, securely connected to the pressure cylinders and having
• two side panels pivotally connected to the front end of the main frame, the side panels each respectively facing the pressure cylinders and also each respectively facing the side faces of the outlet device, and each side panel having an inner surface;
• and
• a limiting board mounted on the inner surface of a corresponding side panel that faces the first pressure cylinder, and facing a corresponding side face of the outlet device;
• and
• a pressure relief device mounted on the outlet device near the first pressure cylinder and having
• a base securely mounted on the side face of the outlet device that faces the limiting board, the base having a leaking channel formed through the base, communicating with the outlet device, and having an internal surface;
• a ball mounted in the leaking channel of the base;
• an adjusting rod movably mounted in the leaking channel of the base and having
• an inner end mounted in the leaking channel of the base;
• and
• an outer end extending out of the base and facing the limiting board;
• an anti-slip-off element securely mounted around the outer end of the adjusting rod and having an outer side facing the limiting board;
• and
• wherein a length of the adjusting rod that extends into the leaking channel of the base is longer than a distance that is defined between the limiting board and the outer side of the anti-slip-off element.