Sodium cooled exhaust valve
The demands made on the exhaust valves are a great deal higher than those made on the inlet valves. This is not surprising since they have hardly any contact with the cooling fresh gases. They transfer their heat of up to
700° C, mainly through the valve-seats. This is a good distance from the valve shaft, which also cools. To shorten this, and to make the cooling process easier, a sodium filling is used to help out.
Making a direct comparison, it can sometimes be seen from the outside that these valves have a hollow cavity, if they have a distinctly thicker shaft. In modern engines
this is no longer as
pronounced. The hollow cavity is filled to just under two-thirds with sodium. At a temperature of over 97° C is turns into liquid and through the movement of the valve when opening and closing, it is thrown to and fro.
Compared, e.g., with steel, the much better heat conductivity coefficient supports this process. How fortunate, that the hollow cavity is sealed so tightly (see picture 2), since sodium, in the open air, burns very well and, if water
is added, even better. 03/12
|Although this technology would appear to be suitable for high-performance engines, it is actually, more appropriate for slow-running engines. The disadvantage is, that the hollow
valve-shafts are either weakened or are too thick.