Re: sodium-filled exhaust valves?

[SailingFC@aol.com]

jorel140@yahoo.com writes:

> Why do they put sodium in exhaust valves? Does this
> have somthing with cooling? Just came across this in
> the Bentley, along with the instructions not to
> dispose of more than ten at a time in a bucket of water.


Sodium is used for cooling.  The inside of the valve stem is hollow and is 
partially filled with sodium.  When below ~98C, the sodium is solid.  As the 
engine heats up and the valve goes above 98C, the sodium liquifies and starts 
sloshing around in the stem.  This sloshing from top to bottom, actually 
helps transfer more heat than if the stem was solid.  By sloshing to the 
upper half of the stem, more heat can be transfered out of the valve, into 
the valve guides and head.
Sodium reacts violently to water and will actually "burn" if it contacts 
water.  Not too sure what is meant by the "ten at a time in a bucket of 
water" since the sodium is sealed inside, unless there may be holes or cracks 
in the valve stem.
Sodium valves are a good thing.
HTH.

-Dick-
78 Scirocco
Original Owner
http://member.aol.com/sailingfc/