Abstract: A closed-circuit type respirator includes an oxygen enriching valve provided in an exhalation system of the respirator, preferably at the lower front end of a respirator mask. This oxygen enriching valve comprises a housing having a passage communicating to the exhalation system and a passage communicating to the atmosphere, a first valve which is provided in the passage communicating to the exhalation system and opens only when pressurized for exhalation and a second valve which is provided in the passage communicating to the atmosphere and is opened for a desired period of time by an external force such as manual operation so that the space inside the housing communicates with the atmosphere.

Abstract: A static pressure automatic control device for respirators of closed-circuit type comprises an exhaled air passage which is branched out of an exhalation system of a respirator and a static pressure discharge valve connected in series to this exhaled air passage. A respiratory dynamic pressure generated by exhalation is attenuated due to resistance encountered while the exhaled air is being passed through the exhaled air passage and substantially the static pressure only is applied to the discharge valve. When the static pressure exceeds a predetermined value, the discharge valve opens to let out a part of gas and thereby decreases the static pressure to the predetermined value.