Air breather plug assembly for use in power transmission unit

An air breather plug assembly adapted for use in a casing of power transmission unit, comprising:

• a cylindrical plug body detachably threaded into an upper portion of said casing and having an inner end portion which extends into an interior of said casing by a predetermined length;
• a cylindrical member fixedly coupled within an outer end portion of said plug body;
• a cup-shaped baffle-plate fixedly coupled within the inner end portion of said plug body, said baffle-plate having a head portion formed with a slot for permitting the flow of air passing therethrough and being positioned in an interior of said plug body;
• a cup-shaped seal member of elastic material fixedly coupled within an outer end portion of said cylindrical member and having a head portion positioned within the outer end portion of said cylindrical member and being spaced from the head portion of said baffle-plate by a predetermined distance to form a cavity therebetween, the head portion of said seal member being formed with a slit to be opened by an internal pressure applied thereto from the interior of said casing through said baffle-plate;
• and
• a cap fixedly coupled over the outer end portion of said cylindrical member and being engaged with the head portion of said seal member in such a manner as to allow the air to flow from said cavity to the exterior through the slit of said seal member.