Re: Compression checks (Alfa content fading)

["Dean W. Cains" <dwc@domain.elided>]

Hi Fred:

That's a good question.  In terms of absolute pressure in the cylinder 
(i.e. as compared to a true vacuum, or 0.0 mm Hg) the pressure after the 
compression stroke of the piston has to be lower.  You're starting with 
less pressure at high altitude, so you'll end up with less pressure.

But there's a wrinkle in there somewhere.  The scale on your Sears 
compression gauge has a 'zero' reading that's referenced to normal 
atmospheric pressure, maybe at sea level, maybe not.  Take your compression 
gauge with you on your next trip to the Keck Observatory on Mauna Kea at 
13,800 feet, and see if the 'zero' reading isn't lower than the 'zero' 
reading before the ascent.  The gauge should read lower after the 
compression stroke, too, as described above, but it might read higher than 
it should in absolute terms.  The diaphragm and spring in the gauge have 
less atmospheric pressure to "work" against, and that may make its readings 
nonlinear.

The real question is, will a Spica pump work properly atop Mauna Kea?  Is 
there enough range built into the atmospheric capsule?

Regards,

Dean
'74 Spider, with a Spica pump that's happy at Florida sea level


At 08:29 PM 11/12/2002, you wrote:

> Date: Tue, 12 Nov 2002 17:35:21 -0500
> From: Ferdinando Di Matteo <aroctech@domain.elided>
> Subject: Compression checks
>
> Here is one to kick around, if I get a high reading at sea level, then
> drive up to  a 14,000 foot mountain top.  would I get a higher or lower
> reading then?   Fred
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