| 摘要 |
Valve assembly (2) for selectively opening and closing a radial aperture (84) provided on a drilling element (8) for drilling mud circulation. Said valve assembly (2) comprises a valve body (3) that comprises an inlet aperture (3A) and an outlet aperture (3C), and a duct (3B) for putting said apertures (3A, 3C) in communication with each other, thereby defining a mud path (p). The valve assembly comprises at least two shutters (4, 6) arranged in cascade along the direction of the mud path (p), thus forming at least a double barrier. |
