Patent ID: 7823859

Claim:
A normally-closed valve having a microflow rate adjusting device, including: a valve stem for opening and closing a fluid passage; a biasing device for biasing said valve stem in a direction to close said fluid passage; a piston body which is engaged in a cylinder in an air-tight manner to form a pressure chamber for moving said valve stem in a valve opening direction against said biasing device; and a stopper mechanism, provided on said cylinder, for controlling a limit of movement of said piston body in said valve opening direction, wherein said stopper mechanism comprises: a stroke adjustment member which is screw-engaged with said cylinder coaxially with said valve stem so that a position of said stroke adjustment member relative to said cylinder can be adjusted, and includes an annular tapered surface at an end of said stroke adjustment member which faces said piston body; a movable valve opening control surface provided on said piston body to be positioned radially outside of said annular tapered surface; a stationary valve opening control surface provided integrally with said cylinder to face said movable valve opening control surface, at least one of said movable valve opening control surface and said stationary valve opening control surface comprising a tapered surface which is tapered to reduce a distance between said movable valve opening control surface and said stationary valve opening control surface in a direction toward an outer edge of said tapered surface; and a plurality of balls capable of coming in simultaneous contact with each of said annular tapered surface, said movable valve opening control surface and said stationary valve opening control surface.