Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 03 Dec 2002 22:02:55 -0500
Message-ID: <redirect-1894060@logan.com>
From: JIMRHER@aol.com
Subject:  IV-P Cabin Air System Dukes Valve
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I have looked into this subject since I have 154 hours on my all electric 
IVP. The Dukes engineer that designed the valve was very nice to me on the 
phone and answered all my questions.

First you need to know what the problem is. Without any vacuum to the valve 
and having it just vented to the cockpit the valve works just fine once it is 
pressurized. The only problem is when you are pushing the power in on take 
off. When you pass about 25 inch you get a cabin "over pressure" then the 
controller works fine after that. My passengers are warned about it and then 
they forget about it.

The valve was designed to have vacuum on it before pressurization to lift the 
valve off the seat. The valve works by an electric motor after that. He said 
that it only needs vacuum at the "power up" stage. 

You can't use the door seal pump that is doing the door seal because mine 
stops when the seal is pumped up. Someone in the past used a dedicated door 
seal pump using the vacuum side to do this and it worked fine but the pump 
requires as pressure switch or runs all the time. I was looking for a better 
solution and I think we found it. Tim Ong at Lancair came up with the idea of 
using a venturi in the pressurization hose to pull a vacuum and I understand 
that he tested a prototype and it produced enough vacuum. I haven't talked to 
him since but the current thought is to mount the venturi in the rear seat 
inlet hose of the cabin and run a short line to the Dukes valve. No motors or 
power and very simple and not much weight. My only concern now is will the 
vacuum build up, be soon enough to prevent the over pressure. 

Tim I'm waiting, but thanks a bunch.

Jim Hergert
N6XE, "An Sex Y" L4P