A feedstock feeder for supplying feedstock to a system operating at a level of pressure. The feedstock feeder includes a pressure vessel having a pressure which is higher than the level of pressure; a mechanical feeder portion which meters the flow of feedstock to the system, the mechanical feeder portion located within the pressure vessel; a feedstock supplier which supplies feedstock to the mechanical feeder portion, the feedstock supplier located within the pressure vessel; a drive mechanism for driving a dynamically moving portion attached to the drive mechanism, the dynamically moving portion coupled to the mechanical feeder portion for moving the mechanical feeder portion; and wherein all dynamic seals operating to seal about the dynamically moving portion are positioned within the pressure vessel.