Cryogenic pump having maximum aperture throttled port

Abstract From the Canadian patent

A low-temperature pump having a throttling valve formed by tilting radially disposed vanes in side-by-side relation capable of fully opening a, pump port to a process chamber. Motion from one vane can be coupled to the next through shims which support the vanes and form a seal when the vanes are flat in a common plane. One of the vanes may be controlled independently of the others so that coarse and fine modes of operation may be achieved by separately controlling (N-1) vanes and the Nth vane. The vanes are maintained in thermal contact with a chilled outer wall surface of a first pumping stage of a twostage pump, the second stage coaxially surrounding a first stage maintained at a very low …