Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Thu, 30 May 2002 10:19:49 -0400
Message-ID: <redirect-1251727@logan.com>
From: Gary Wolf <gwolf@vallnet.com>
Subject: Re: Backup vacuum in IVP
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Brent-
Could you elaborate?  I assume this is a "standby" system with a second 
regulator.  Where is the regulator mounted? Outside the cabin or inside?  I 
initially wanted to mount my regulator and filter inside the cabin on my 
main system, thinking the inside pressure would "help" the pump, but was 
told all that would do was make the pump work harder, and everything has to 
be outside the cabin.  I know I'm missing some concept here.  Can you 
help?  Thanks.

>Having said that, I did have the opportunity to design a vacuum system
>for a friends IV-P. He wanted a flight director so a vacuum system was a
>must have. I configured it with a vacuum regulator, filter and a small
>sonic venturi so that the system used filtered cabin air and discharged
>into the engine compartment. The advantage to this configuration was
>that when the vacuum pump failed (not IF) the cabin pressure would run
>the system. Free standby vacuum, works great. The bad news is that you
>have to watch for a vacuum flag when you transition to unpressurized
>flight in case the pump went T.U. in cruise.