Dan Truesdell wrote:
Thanks for the heads-up on those. I was figuring on about $2K, but $4K
would mean asking the other 4 owners to kick in $1000 for an item that
they won't use. For a 172, it's probably just as good then to get a
manifold-driven backup vacuum.

Consider the dual-rotor vacuum pump from http://www.aeroadvantage.com instead.

I've owned one of the manifold-driven backup vacuum systems, and it's marginally
OK, but I wouldn't buy one again. The shuttle valve gets stuck. It requires
pilot action to preflight test it, and to switch it on when you need it. The
vacuum it provides is limited. There is no provision for practicing with it (you
have to physically disconnect the vacuum pump), so you don't get proficient with
flying with the reduced vacuum and altered operational requirements. Under
most operational regimes, you will have to limit engine power in order to keep
the vacuum sucking.

By contrast, the dual-rotor pump failover is automatic, you get full vacuum
without interruption, just a panel annunciator to check during preflight and to
tell you one of the rotors has failed.

The cost is only slightly more than the manifold-dirven system.

Dave
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