Question

How is gas introduced into the glass tubing used in neon signs?

Answer 1

Neon tubes are capped off by two glass electrodes that have wirepassing from outside to inside. One of these electrodes hastubulation - a small tube which remains as a passage from outsideto inside. Tubulations are sealed to a pumping system. The pumpingsystem has glass stopcocks or valves that allow sections to beselectively opened or closed. An ultrahigh vacuum pump pulls airout of the tube while a high voltage transformer bombards and heatsthe remaining air - to produce temperatures in excess of 500ºF.This allows the tube to achieve a higher degree of purity. When ahigh vacuum is reached, and the tube begins to cool, a small amountof inert gas is introduced from a flask or a tank of pressurizedgas. The tubulation is then heated and as it is pulled it suchinward to make the tube's own seal.