A telescopic assembly for pipes for conveying powdery to granular materials entrained in an air or like gaseous stream comprises two pipes of different diameters coaxially fitting one within the other and axially slidable relative to each other, a labyrinth packing provided around a front end portion of the inner pipe for preventing leakage of the stream or ingress of the atmosphere through the clearance between the two pipes, and a scraper attached by a plate spring to the retainer ring of the labyrinth packing on the front end of the inner pipe and in pressing contact with the inside peripheral surface of the outer pipe. Rollers carried by the outer pipe engage the outer surface of the inner pipe and aid in maintaining a uniform clearance between the two pipes.