Flow control valve

摘要

A valve for use in a tunnelling machine to permit back-flushing without blockage or breakdown comprises a core (67) rotatable in a casing (61), the core having an axial in let passage (76) leading to an obtusely angled passage (77) which communicates selectively, via an opening (74), with circumferentially spaced, similarly inclined openings (64) in the casing. A polymeric sleeve (68) is secured to the core between it and the casing and has an opening (78) aligned with the angled passage (77) in the core, so that in any open position of the valve, the three aligned openings (74, 78, 64) define a continuous cylindrical flow passage.