[TheForge] Sodium filled valve stems?

[Andy Vida]

Barking Crow wrote:
> 
> Hey,
> 
> What's up with the sodium filled valve stems?  Why do they do it? 

	The valves are hollow and filled about halfway with sodium.
	As the valves warm, the sodium melts and sloshes around inside
	the evacuated cavity, sinking heat up into the stem and away
	from the head.  They are used in the exhaust valves of large
	aircraft engines.  I have a huge one from an old 3000hp Pratt
	& Whitney triple Wasp of WWII vintage, and one from a much
	smaller 9 cylinder Franklin.

> How can I tell if one is sodium filled? 

	Two ways that I can tell, visually speaking.  One, the face of
	the valve will be convex rather than concave.  This is to
	provide enough volume of both sodium and slosh space.  The other
	way, but less reliable, is to look at the valve stem.  If a
	separate end is attached, it could be the cap on the hollow
	stem.  It could also be just a tough wearing cap on a solid
	stem.  If you have convex face and a cap, I would assume it
	is a sodium-filled valve and proceed accordingly.  If you 
	can only see a convex face, I would still assume it is sodium
	filled.  Some of those joints are not readily visible.

	If you have a valve that has a very small apparent mass in
	the head and leading to the stem, and a concave face, you
	probably do not have sodium there.  Always be careful.

> What happens to my day if I cut one that is sodium filled? 

	Your day could be ruined.  Sodium burns with very little
	provocation.  It can spontaneously combust just sitting
	on your table in the air.  This is why it is often stored
	in kerosene.  Sounds counter-intuitive, but kero works.

	It burns violently and water will not put it out, but can
	make the fire worse.

> And finally, what are regular valves made of?

	All sorts of things.  High alloy steels, nimonic alloys, titanium...
> 
> Thanks again,
> 
> Jeff Valentine
> 
> Barking Crow
> http://www.barkingcrow.com
> mail@barkingcrow.com
> 
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--
	-Andy V.
	 Eventide Forge
	 Mad Science Inc.
	 Scottsdale, AZ

	foolish being...
	you can't get away with your snobbery any longer. Your thoughts on life
are 
	only thoughts coming from one person . Your opinion is only one out of
the 
	billions of other minds out there. You may think you can take over the
world 
	Pinky, but you will fail.

			-Seshat McDaniel, the daughter I never had that manages to
				          follow me around the house like a bad cold.