The primary function of the extractor-feeder is to feed seed cotton to the gin stand uniformly and at controllable rates, with extracting and cleaning as a secondary function. The feed rate of seed cotton is controlled by the speed of two star-shaped feed rollers located at the top of the feeder directly under the distributor hopper. These feed rollers are powered by variable-speed hydraulic or electric motors and controlled manually or automatically by various interlocking systems within the gin stand. The drive may be designed to automatically start and stop as the gin breast is engaged or disengaged; the system may also be designed to stop feeding seed cotton in cases of gin stand overloads or underloads. Many of the systems are designed to maintain constant seed-roll densities. This is usually accomplished by regulating the speed of the feed rolls in response to feedback control signals from the gin stand. The signals are based on monitoring the power consumption of the electric motor driving the gin stand, measuring displacements of the cove board in the seed-roll box, or monitoring the pressure required to drive the hydraulically powered seed-roll agitator.

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