Diffusion Pump

A rotary vane pump stops improving at the vapour pressure of its own oil, and no amount of running gets it lower. Wolfgang Gaede's diffusion pump of 1915 goes far below that by abandoning mechanical pumping entirely. Oil is boiled at the bottom, its vapour rushes up a central chimney and out through angled nozzles as a high-speed downward jet. Gas molecules wandering into that jet are struck and knocked downward, carried to the bottom where a backing pump removes them, while the vapour condenses on the cooled walls and runs back to the boiler. There are no moving parts whatsoever — the only thing moving is vapour — and it reaches pressures a million times lower than the pump backing it.