PURPOSE: To attain a wide range of pressure control by mounting two semicircular valve bodies of a stationary blade and a moving blade inside a cylindrical valve easing so as to make the moving blade rotate as a rotating shaft coaxial to the central shaft of the valve easing.

CONSTITUTION: A semi-circular stationary blade 7 is mounted inside a cylindrical valve easing 6, and the arc-shaped outer periphery edge of the stationary blade 7 is jointed to the inner wall of the valve easing 6. A semi-circular moving blade 8 is mounted so as to br rotated by a rotating shaft 9 coaxial to the central shaft of the valve casing 6. The moving blade 8 and the stationary blade 7 are mounted so as to form no clearance between them. When the moving blade 8 rotates, an open part (a) occurs between the moving blade 8 and the stationary blade 7. By controlling the rotational angle θ of the moving blade 8, the open part (a) of suitable size is generated to form proper piping resistance, so it is possible to attain precise pressure control over a wide range.