Abstract: A cryogenerator pumping system comprises at least two cryopanels, maintained within an enclosure having an open end which is adapted for attachment to the chamber to be pumped and which embodies a throttling device effective to restrict the flow of gas from the chamber to the cryogenerator pump, a relatively higher temperature cryopanel within the enclosure being arranged to project beyond the plane of the throttling device whereby to be capable of condensing water and other volatile vapors produced in the chamber and thereby prevent the deposition of such vapors upon the throttling device.