Jon Elson wrote:

Tom wrote:

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



This, in a reciprocating valve? What would keep the sodium at the head
end of the valve?

Yes, exactly. The valves are hammered with hundreds of G's every time
they slam open and shut. Convection would be totally insignificant
under such extreme acceleration. Every time the valve opens, the sodium
is thrown against the rocker arm or lifter, every time it shuts, it is
slammed back to the head. (Maybe it bounces, and makes TWO round trips
every valve cycle.)

Jon

I recall first hearing about sodium filled valve stems in relation to IC
aircraft engines and some racing cars. I just did a little Googling.

Further supporting the theory that "You've got to take the bad with the
good", I found this text related to aircraft engines which claims that
sodium cooling the valve heads can accelerate valve guide wear.

It's from this web page:

http://www.prime-mover.org/Engines/Marvel/tbo3.html

**********************************

The Problem of Sodium Filled Valves

As revealed above, sodium filled valves in the O-320 engine did not
eliminate valve distress problems. To the contrary, our question is
whether or not they either cause or increase these problems. Sodium
filled valves are an extremely expensive component that we believe are
greatly to blame for valve/guide distress incidents. They do not make
heat magically disappear, as some would have you believe. All these
valves do, at great monetary expense, is transfer heat from the valve
head to the valve stem, or more generally, from the combustion chamber
to the cylinder head via the valve guide. They merely move heat from
point "a" to point "b." It still has to be eliminated from the cylinder
head by either air cooling or oil cooling or both. The problem is that
valve guides are wearing out prematurely and are doing so in spite of
operators keeping CHT levels in the proper range. Excess heat is the
primary cause of premature guide wear (in a properly assembled
cylinder), as most engine shops will tell you. The problem with sodium
filled valves is that they serve to import even more heat into the guide
by transferring it up from the valve head. Lycoming's long history of
valve/guide failure incidents in the parallel valve cylinders has shown
that there is simply no way that the guide can shed all of its higher
heat load via the cooling fins alone, and Lycoming's design provides for
very little oil to aid in that process. The irony here is that
Continental uses solid stem valves that dissipate most of their heat
into the valve seat. Relatively little comes up the stem and into the
valve guide and yet Continental has an abundance of oil in this area to
aid in heat transfer. If sodium filled valves are needed at all, one
wonders why Continental doesn't use them, since their barrel style
hydraulic lifters provide substantial oil for additional cooling of the
guide and valve. Lycoming's mushroom style lifters do not. We think that
without any change in oil flow to the rocker boxes, Lycoming valve and
guide longevity might well benefit from simply going to solid stem
valves. Unfortunately, these are not available.

************************************************** ****

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"