Mechanical servo means

Claim 1

In a mechanical servo means of the type including a booster body, a valve body having a hollow portion at its end, a push rod inserted at its one end into the hollow portion of said valve body in a slidable and coaxial relation therewith, a diaphragm having an outer periphery secured to said booster body and an inner periphery secured to said valve body to form a first chamber and a second chamber in said booster body, a finger plate abutting at a portion thereof on a side wall of said diaphrgm and slidable with respect to said push rod, a fulcrum plate secured to said push rod and urged by a return spring in one direction to engage at its outer periphery with the finger plate at a first fulcrum point located radially inwardly from a point at which the resultant force of the pressure on the diaphragm acts, said valve body being provided with passage means for communicating said second chamber with atmosphere, said finger plate having means for opening and closing said passage means, said opening means being adapted also to control the communication between the first chamber and the second chamber; the improvement which comprises resilient means disposed between said finger plate and the fulcrum plate so as to form a second fulcrum point which is radially deviated from said first fulcrum point whereby an effective fulcrum is provided which is displaced from the second point to the first point when the resilient force is overcome by the force exerted by the finger plate toward the fulcrum plate, said resilient means including a rubber ring of triangular crosssection, the outermost annular edge of the rubber ring being in engagement with the finger plate to provide the second fulcrum point.