Normally-closed valve having a microflow rate adjusting device
A normally-closed valve having a microflow rate adjusting device includes a valve stem for opening and closing a fluid passage; a biasing device for biasing the valve stem in a direction to close the fluid passage; a piston body which is engaged in a cylinder in an air-tight manner to form a pressure chamber for moving the valve stem in a valve opening direction against the biasing device; and a stopper mechanism, provided on the cylinder, for controlling a limit of movement of the piston body in the valve opening direction. The stopper mechanism comprises a stroke adjustment member which is screw-engaged with the cylinder coaxially with the valve stem so that a position of the stroke adjustment member relative to the cylinder can be adjusted, and includes an annular tapered surface at an end of the stroke adjustment member which faces the piston body.
1. 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.
2. The normally-closed valve having a microflow rate adjusting device according to claim 1 , further comprising an end cap which is fixed to an end of said cylinder to close said end of said cylinder,
wherein said stroke adjustment member is screw-engaged with said end cap, and
wherein said stationary valve opening control surface is formed on said end cap.
3. The normally-closed valve having a microflow rate adjusting device according to claim 1 , wherein said stroke adjustment member comprises an end cap which is screw-engaged with an end of said cylinder to close said end of said cylinder, and
wherein a fixing member including said stationary valve opening control surface is fixed to said cylinder to be positioned inside said stroke adjustment member and radially outside of said annular tapered surface.
4. The normally-closed valve having a microflow rate adjusting device according to claim 1 , wherein one and the other of said movable valve opening control surface and said stationary valve opening control surface are formed as a part of a circular conical surface and a plane orthogonal to an axis of said valve stem, respectively.
5. The normally-closed valve having a microflow rate adjusting device according to claim 1 , further comprising guide grooves, provided inside said cylinder, for limiting directions of movements of said plurality of balls to radial directions of said cylinder.
6. The normally-closed valve having a microflow rate adjusting device according to claim 1 , wherein angles of said annular tapered surface and said tapered surface of said at least one of said movable valve opening control surface and said stationary valve opening control surface are determined so that a ratio of an amount of axial movement of said stroke adjustment member to an amount of axial movement of said piston body becomes a ratio of 1 to 1/2 through 1 to 1/50.