Fluid reservoir for brake master cylinder

A fluid reservoir for mounting on a brake master cylinder, the reservoir comprising:

• a casing for storing an amount of brake fluid therein, said casing having an upper opening;
• a cap detachably coupled over the upper opening of said casing to close said casing, said cap being provided at the center thereof with a vertical rod extending axially into said casing and having a pair of axially spaced recesses at its intermediate portion;
• an extendable diaphragm seal member coupled in a fluid-tight manner within said casing to subdivide the interior space of said casing into an upper chamber vented through a portion of said cap and a lower chamber located above the liquid surface of the brake fluid, said diaphragm seal member being provided at its inner periphery with an annular valve part movable along the intermediate portion of said vertical rod and cooperating with the recesses of said rod to permit the flow of air to and from the lower chamber;
• resilient means for normally retaining the valve part of said diaphragm seal member between the recesses of said rod to close the lower chamber wherein said resilient means comprises first and second coil springs concentrically assembled with said vertical rod, said first spring being loaded to bias the valve part of said diaphragm seal member in the downward direction, and said second spring being loaded to bias the valve part of said diaphragm seal member in the upward direction;
• and
• a cylindrical spring receiver concentrically assembled with said vertical rod to contain said first spring therein and secured at its lower end to the valve part of said diaphragm seal member, and an annular retainer engaged with a stepped portion of said vertical rod and received by an upper end portion of said receiver in such a manner that upward movement of said receiver is guided by said retainer, and wherein said first spring is disposed with a predetermined load between the lower end of said receiver and said retainer.