Getter

Every pump in this batch stops working the moment the tube is sealed off — and a sealed vacuum immediately begins to fill again, as gas seeps from the glass, the metal and the joints. A radio valve or a lamp would go soft within weeks. The getter solves it chemically rather than mechanically: a small quantity of a very reactive metal, usually barium, is flashed onto the inside of the envelope after sealing, depositing a mirror-bright film that chemically absorbs stray gas molecules as they appear. It is a pump with no moving parts, no power supply and no connection to the outside — it works silently for the tube's entire life, and the silver patch inside every old valve is it.