In a moving matrix magnetic separator in which a matrix device moves relative to a processing device and a seal assembly seals a longitudinal section of the matrix device to an associated processing device, the seal assembly including a sealing surface on one of the devices and a seal on the other, the improvement comprising said seal including a base portion extending generally longitudinally in the direction of motion of the matrix device; first and second salient, resilient lip portions extending from the base portion toward an associated sealing surface in the gap between the matrix device and the processing device, and extending generally longitudinally to the direction of motion of the matrix device and spaced from each other transversely to the direction of motion of the matrix device and forming a channel therebetween; a pressurized purge fluid chamber formed by the channel and the associated sealing surface; and means for supplying purging fluid to the purge fluid chamber formed by the channel and lip portions with the associated sealing surface.