"The original question was, if you are going to have a backup, what kind of backup is preferred."


Group,

When we built our IV-P, the back-up system was a "wet" vacuum pump, which operated the artificial horizon.  The wet pumps have an excellent service life, having gone several thousand hours without overhaul.  We simply plumbed the discharge of the pump into the oil separator that was already there for the crankcase vent.  It worked for us and has also worked for a IV-P friend of ours who has over 1000 hours on his IV-P.  Before we installed the wet pump on his IV-P, he was losing pumps quite frequently.
It's old technology, but it works and doesn't require electricity.

Ed Smith
Chesapeake, VA