I am trying to figure out how Helium Leak Detectors work. If a leak detector is pumping on an enclosure that is at a low pressure, the detector will detect helium leaking into the system instantly as far as my human senses can tell. The helium will propagate 4 meters in a time so small I can't even sense. How is this possible? There can't be very much airflow through the system because the leak is so small. does helium propagate this quickly through air? or is simply because the pressure is low in the enclosure? why?