Dave Butler wrote:
Robert M. Gary wrote:

Dave Butler wrote in message
...

I now have the Aero-Advantage STCed dual-rotor vacuum pump and think
it is overall the best solution. It offers more redundancy and more
reliable backup for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a
better solution, IMO.



I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.

BTW: What is the purpose of the dual rotor pump. When my pumps have
gone out its always been because a vain got stuck and sheared off the
pump shaft. My mechanic said that's how they usually fail. Wouldn't
that kill both rotors?
-Robert


I understand your skepticism, but AeroAdvantage claims that they have a
mechanical arrangement that allows each rotor to fail independently.
Check the web site for more details, but if my memory serves it amounts
to providing weak points (necking) in the shaft in such a way that the
shaft for each rotor can fail independently. I have had trouble
visualizing what the mechanical arrangement is and would like to take
one apart or see an exploded drawing to see how they do that. I can't
explain exactly how it's done, but they convinced me to my satisfaction
that they had solved the problem.

Following up my own posting: here's what it says in the FAQ at
http://www.aeroadvantage.com (to visualize, the pump is mounted so that the
drive shaft is pointing forward):

1.) How can the rear pumps chamber continue to operate after the forward pump
chamber has failed?

The Dual Rotor Vacuum Pump incorporates a shear coupling between the forward
rotor and the driveshaft. The forward rotor’s shear coupling can shear away from
the driveshaft without causing the driveshaft to fail. Similarly, the rear rotor
also incorporates a shear coupling. As an Additional safeguard, the shaft has a
necked down area between the two rotors. Either the rear rotor’s shear coupling
or the necked area in the driveshaft can shear away from the forward rotor
without effecting the forward rotors continued operation.

and also:

6.) When a vacuum pump fails it can contaminate the vacuum system how do you
prevent one vacuum pump chamber from contaminating the other in the event of a
failure?

The Dual Rotor Vacuum Pump incorporates an intake manifold with dual check
valves. When a rotor disconnects from the driveshaft the check valve for that
chamber closes, preventing contamination of the other pump that is still
operating. Also, since the pump's chambers share a common exhaust, the exhaust
from the operating pump helps contain the contamination to the failed chamber by
applying positive pressure to the failed chamber.

Dave
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