Gary writes:
<<<The device is basically a pressure regulator that automatically selects pressure from 3 or 4 sources and picks the appropriate pair of sources to produce the required differential pressure.>>>

Cool idea Gary. I am a big fan of redundant electrons but your invention could make it a close comparison. The advantage of redundant alternators is that you can use the redundant system for more than the AH. This may also be the bad news.

When I designed the vacuum system for Derek's IV-P I configured the pump and regulator such that the cabin pressurization would drive the HSI / flight director.  This has three drawbacks, you won't know you have a pump failure until you are coming off of pressurization, in the event of a failure you must set the pressurization controller to the lowest airport elevation available and when the manifold pressure drops below the outside pressure you will lose pressurization and vacuum gauges. The good news is it is free and better than nothing.

Regards
Brent Regan

BTW. How DO you pump a vacuum? It is like my kids when I ask " Watcha doin?" comes the reply "Nothing."

BR