Bill Freeman wrote:

These units were pretty reliable and designed to fail in the full cold
position.  The are a brass bellows about 2" in diameter and about 1.5"
long collapsed (cold).  One end has a 8mm female thread in a center
boss with two flats, mounts in a steel loop bracket in the outflow air.
When it gets hot it expands, closing down flaps in the airflow.  The
operating rod end has a ~3mm female thread and total motion is about
3/4".  When failed it expands fully.  Neat units, the same from the 50s
thru the 80s, probably still used in the Brazilian aircoolers, still in
production, last I heard.

I'm not familiar with these units, but it sounds like the bellows is
trapping a low (versus sea level) pressure gas, and is harnessing the
gas' thermal coefficient of expansion to counteract the bellow's
otherwise natural tendency to expand (thus the failure mode).  What I
immediately wonder is whether the bellows will work at altitude.  I think
not.

Russell Kent

Good point Russell. It should expand at high altitude. VW drivers in
Colorado ought to know as their engines should not warm up if that is the case.
Anybody drive a air cooled bug or Porsche in Colorado?
I guess I could test one with a shop vac.

BTW they can be had from Gene Berg http://www.geneberg.com
for $20 each. I think I will use two on each flap to get plenty
of work out of them. (work = force times distance)

Paul Lamar

I think it is a liquid with a phase change at the desired temperature.
Pressure would make little difference, but some.

Bill
Long EZ builder & pilot
BSME, MSME

Like a bit of water than turns to steam at 212 F. Yes!!! :-)

Paul Lamar
 
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