Fuel tank cap for two-way gas intake and exhaustion

A fuel tank cap for two-way gas intake and exhaustion comprising:

• a body including a first lid and a second lid, the first lid having a coupling orifice configured to connect with a pressure adjustment module, the pressure adjustment module having a rotatable knob and a limiting unit, and the first lid having a locking rib formed on a bottom of an inner wall thereof;
• a first spring being defined between the inner wall of the first lid and the second lid, a first end of the first spring being fitted on an inner wall of the limiting unit, and a second end of the first spring being fitted on an upper end of the second lid, the second lid being fitted with the inner wall of the first lid, and a bottom of the second lid retaining with the locking rib;
• the second lid including an accommodation groove formed on a central portion thereof, and the second lid including a connection portion arranged on an inner wall of the second lid;
• wherein the accommodation groove of the second lid accommodates a flexible adjustment valve and a second spring, and the flexible adjustment valve has a main part and a flexible stop unit, wherein the flexible stop unit is connected with the main part, and the flexible stop unit has a movement travel in which the flexible stop unit expends or retracts, the main part has at least one seal loop fitted on an outer wall thereof so as to matingly contact with the accommodation groove, and the main part has a defining rib, wherein a first end of the second spring abuts against the defining rib, and a second end of the second spring is biased against the limiting unit.