Positive and negative pressure switching mechanism of gas mask

The invention discloses a positive and negative pressure switching mechanism of a gas mask. The mechanism comprises a mechanism body, the center of the mechanism body is provided with a cylindrical cavity, a rotating disc is arranged in the cylindrical cavity, arc grooves are symmetrically formed in the two sides of the inner wall of the cylindrical cavity, and convex ribs located in the arc grooves are symmetrically arranged on the side wall of the rotating disc. A connection rod is inserted into a center hole of the rotating disc through interference fit, a boss above the connection rod is in fit with the bottom face of the rotating disc, the lower end of the connection rod penetrates out of the mechanism body through clearance fit, the mechanism body is provided with a switching rotaryknob, two convex rods of the switching rotary knob are inserted into two holes in the rotating disc through clearance fit, the lower end of the connection rod is fixedly provided with a valve pressingsheet, the lower portion