Re: O-rings

[jack@domain.elided (Jack Hagerty)]

From: John Katos <JJK1204@domain.elided>

>O-rings are not usually designed to seal flat surface to flat surface. 

True.

>In most cases a groove is used to retain the o-ring position. 

In *all* cases, if you want them to work right.

>O-rings do not form a perfect seal, there is almost always some leakage, 
>unfortunately NASA now understands the ramifications of this dynamic. 

This I don't understand. I use O-rings by the bushel to seal high vacuum
systems against air, plasma and nasty gasses at pressures below that where the 
shuttle flies. Unless you consider stopping all but two or three molecules of 
air a minute "not sealing" I'd like you to clarify that statement. Granted, 
if you used them without a groove  they're not going to seal because that's 
not how they were designed to work so please don't generalize.

As for the slam against NASA, those booster segments are sealed with a 
dual O-ring each about the thickness of your wrist. At ignition, the 
segments actually stretch apart about an inch or so, a motion taken up by 
the elasticity of the rings. On the morning of the Challenger launch, the
temperatures had been at or below freezing all night and the rings weren't
elastic enough to take up the strech. The engineering spec said that the 
weren't supposed to launch below 40F. The Challenger was lost to a political 
and management decision, not an engineering one.

- - Jack

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