----- Original Message -----
From: <JIMRHER@aol.com>
To: "Lancair Mailing List" <lml@lancaironline.net>
Sent: Tuesday, December 03, 2002 10:02 PM
Subject: [LML] IV-P Cabin Air System Dukes Valve


> 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.
>
This issue has turned out to be quite intriguing.

If I understand correctly, Tim Ong's idea  might have a drawback, in that
when the outside air is cold, would you want to have cold air running into
the cabin to draw air through the venturi?

With further thought about Tim's approach, teeing off of some cabin air aft
of the bulkhead and running it through a venturi,  could overcome the cold
air problem.  However the effectiveness could change by the amount of air
that is selected to go into the cabin.

With a better understanding of how the dukes valve works,  I have some
thoughts of another approach to get vacuum to  the  valve.  The concept is
to tap off the engine manifold. When the engine is at idle, as every pilot
knows, the manifold pressure is low.  The approach would be to T off the
manifold pressure line going to the manifold pressure gauge, perhaps where
it comes into the cabin.  Then put a check-valve connected to another T.
One side of the T would go to a reservoir, say around 20 ounce capacity,
mounted to the cabin side of the firewall.  The other side of the T would go
to the dukes valve.
This system probably is still used in motor vehicle power brake systems.
The small amount of air being sucked out of the reservoir would have
virtually no effect on the manifold pressure gauge.

Thinking further, it might just be that all the dukes valve needs is vacuum
at engine start-up.  Then no reservoir would be needed.

Some other comments:  The IV-P I flew in, the door seal had to be deflated
periodically to get air exchange in the cabin, while others have said it is
a one-time event to get the dukes valve to operate.  Could it be that  the
pneumatic lines exiting the dukes valve are run differently for those who
have to deflate the door seal periodically versus for those who only have to
experience a one-time pressure surge?

I'm looking forward to us finding a practical solution to this lingering
problem for our high-end birds.  By pooling our knowledge in this open
forum, I feel we will find a good solution and make it available for all in
the future.

Thanks for your help!       Scott Turner