Feed-links for network extensions

In a static sieve assembly having a housing for mounting a sieve or screen, a feed box having a discharge spout for feeding material tangentially to and across the sieve, a side of the spout having flexibly connected fixed upper and movable lower parts, and an actuator on said feed box and acting on said lower part for controlling the rate of feed to the sieve by varying the area of a discharge opening of the spout.