Fluid reservoir for brake master cylinders

Claim 1

In a fluid reservoir for mounting on a brake master cylinder, comprising a casing for storing an amount of brake fluid therein, said casing having an upper opening, a cap member of elastic material detachably coupled over the upper opening of said casing, and a diaphragm seal member coupled within said cap member to close off brake fluid stored in said casing and to subdivide the interior space of said casing into an upper chamber vented through a portion of said cap member and a lower chamber located above the liquid surface of the brake fluid, said diaphragm seal member being provided at the outer periphery thereof with an inlet check valve assembly for permitting the flow of air from the upper chamber into the lower chamber and provided at the central portion thereof with an outlet check valve assembly for permitting the flow of air from the lower chamber into the upper chamber, the improvement wherein said inlet check valve assembly comprises an annular valve seat in the form of a lower stepped portion formed on the inner peripheral wall of said cap member, a cylindrical retainer member of hard material integrally secured to the outer periphery of said diaphragm seal member and having an annular flange facing to said annular valve seat and an upper end resiliently engageable with an upper stepped portion formed on the inner peripheral wall of said cap member, an annular lip of elastic material integrally formed on the annular flange of said retainer member, and resilient means for biasing said retainer member toward the upper stepped portion of said cap member to press said annular lip into contact with said annular valve seat.