WHAT'S INSIDE A VALVE (xii)

Today, I want to look at LEAD IN WIRES.   Look in any PINCH & FOOT valve and you can see the LEAD IN WIRES sandwiched on all sides by the pinch glass.  In order to maintain that seal, the wire has to have a similar coefficient of expansion as the glass surroundings - a tall order indeed!

In actuality, the LEAD IN WIRES are of a composite construction with the top section being of sufficient diameter to make the electrode cage support rigid and similarly with the bottom section of copper wire that forms the valve pin connection.  The middle section of wire however, is made of an alloy that  has an elastic property as well as the same coefficient of expansion as the surrounding glass.  

Typically the alloys are complex and still proprietary information but although we may not know the precise proportions of the eutectic adjunct, we do know the constituent metals and the names of two of these alloys.   Alloys were made of Iron (Fe), Nickel (Ni) and Cobalt (Co) and we have exotically named wires such as Kovar, Fernico, Dumet wire and most impressive of all, Red Platinum.