A valve for controlling flow of a fluid from a supply having a first pressure, said valve having at least three positions, a first position for passing fluid from a supply to a volume wherein a second pressure is to be controlled, a second position for maintaining an amount of such fluid in such volume substantially constant, and a third position for exhausting said fluid from the volume, said valve comprising:
- (a) a housing means having an axis, said housing means having an inner surface having at least a first axisymmetric surface portion at a first axial position in reference to said axis, formed as a surface of revolution in reference to said axis, a second axisymmetric surface portion at a second axial position in reference to said axis, formed as a surface of revolution in reference to said axis, said housing means having an outer surface;
- (b) a first housing supply port formed in said outer surface of said housing means for receiving such fluid from such supply;
- (c) a second housing supply port formed in said inner surface of said housing means at an axial position disposed between said first axial position and said second axial position, said second housing supply port communicating with said first housing supply port;
- (d) a rotor positioned within said housing means;
- (e) a gap between said rotor and said housing, at an axial position between said first axial position and said second axial position;
- (f) first sealing means disposed on said rotor, said first sealing means contacting said housing means on said first axisymmetric surface portion;
- (g) second sealing means disposed on said rotor, said second sealing means contacting said housing means on said second axisymmetric surface portion;
- said first sealing means and said second sealing means serving to confine such fluid from such supply to said gap in a range of axial positions between said first axial position and said second axial position;
- (h) a rotor supply port disposed on said rotor at an axial position disposed between said first axial position and said second axial position,
- (i) a first rotor internal passageway for such fluid from such supply, said first rotor internal passageway communicating with said rotor supply port;
- (j) a third axisymmetric surface portion on said housing means, formed as a surface of revolution in reference to said axis;
- (k) a fourth axisymmetric surface portion on said rotor, formed as a surface of revolution in reference to said axis, said fourth axisymmetric surface portion being disposed adjacent to said third axisymmetric surface portion on said housing means;
- (l) a housing delivery port disposed within a first annular sealing means adjacent said fourth axisymmetric surface portion on said rotor;
- said first annular sealing means providing a seal between said housing delivery port and said fourth axisymmetrical surface portion on said rotor, said housing delivery port communicating with such volume wherein such second pressure is to be controlled;
- (m) a housing exhaust port disposed on said third axisymmetric surface portion on said housing means, said housing exhaust port communicating with one of an ambient atmosphere and a vessel having a third fluid pressure lower than such first pressure of such supply;
- (n) a rotor delivery port disposed within a second annular sealing means, said second annular sealing means providing a seal between said rotor delivery port and said third axisymmetric surface portion on said housing means, said rotor delivery port communicating with said first rotor internal passageway;
- (o) a first rotor exhaust port disposed within a third annular sealing means adjacent said third axisymmetric surface portion on said housing means, said third annular sealing means providing a seal between said first rotor exhaust port and said third axisymmetric surface portion on said housing means;
- (p) a second rotor exhaust port disposed within a fourth annular sealing means adjacent said third axisymmetric surface portion on said housing means, said third annular sealing means providing a seal between said second rotor exhaust port and said third axisymmetric surface portion on said housing means;
- (q) a second rotor internal passageway, formed within said rotor, joining said second rotor exhaust port to said first rotor exhaust port;
- (r) means for positioning said rotor in at least three angular positions:
- a first angular position wherein said rotor delivery port is positioned adjacent said housing delivery port whereby a flow path is provided between said supply and said volume wherein said second pressure is to be controlled;
- a second angular position which is a lap position for maintaining a constant amount of fluid in said volume wherein said second pressure is to be controlled, wherein said rotor delivery port is positioned adjacent said third axisymmetric surface portion and sealed off by contact between said second annular sealing means and said third axisymmetric surface portion, and said housing delivery port is positioned adjacent said fourth axisymmetric surface portion on said rotor, and sealed off by contact between said first annular sealing means and said fourth axisymmetric surface portion;
- and a third angular position wherein said housing delivery port is adjacent said first rotor exhaust port, and said second rotor exhaust port is adjacent said housing exhaust port whereby fluid is exhausted from said volume wherein said second pressure is to be controlled;
- said rotor delivery port, said first rotor exhaust port, said second rotor exhaust port, said housing delivery port, and said housing exhaust port being further characterized in that at least one thereof has a dimension parallel to a direction of rotation of said rotor greater than a dimension perpendicular to a direction of rotation of said rotor.