David R Brooks wrote:
Sodium boils at 883C = 1620F (Kaye & Laby). Do they really run that
hot?

1625F is commonly cited as peak exhaust gas temperature for IC aircraft
engines. The measurement is usually taken several inches from the
exhaust port, so valve temperature could run a little higher.

"Tom Miller" wrote:

:The valve stems are not completely filled with sodium. As the valve heats
:up, sodium vapourizes and rises up the valve stem by convection. This
:carries the heat up to the top of the stem where it is dissipated by the oil
:and air surrounding it. The sodium condenses and falls back to the bottom of
:the valve and collects heat from the seat and continues the cycle. It
:effectively forms a "heat pipe" to transfer the heat away from the seat .
:
:Tom

Most aircraft engines today have horizontal cylinders, thus horizontal
valves.

:"Artemia Salina" wrote in message
:news : Dumb question I guess, but why do engine manufacturers make
: valve stems that are filled with sodium (I think only exhaust
: valves are sodium filled). Is it a heat expansion issue?
:
: Thanks.
:
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