When a cantilevered screw is used as an injector, occasionally, it may be desirable to deliver two products at the same time to the same point. If one of them is liquid and can be pumped, or will flow, then the drive shaft can be made hollow and to accept a rotary joint. With this configuration the screw will control the dry product that it is conveys and a pump or valve will control the liquid thus giving you a two product controlled feed to a single point.
When the cantilevered screw is used as a feeder then the inlet must be filled at all times. The design of the flight pitches under the inlet will control the draw down of the product in the inlet and the subsequent product loading in the conveying portion of the housing after the inlet. There will always be a section of shroud after the inlet; this creates a round conveying path that the screw draws through. With this round conveying path the screw can only convey material that has fallen into the flight pockets in the inlet. Material flow into the inlet of the screw feeder is also critical since the screw feeder can not meter the material out of the inlet unless the material fills the flight pockets in the inlet.