----- Original Message -----
Sent: Friday, December 13, 2002 12:31
AM
Subject: [LML] IV-P Cabin Air System
Dukes Valve with An All Electric Panel
After going over LML Posts, talking to Pat
Patrick at Dukes and applying all this knowledge gathered, I feel quite
certain the following will get the Dukes valve to operate as
designed.
The solution is to simply use the engine manifold
vacuum, tapped off of the manifold pressure line to the manifold pressure
gauge. Put a check valve in after the tap off to prevent a positive
pressure form being applied to the Dukes valve. Run the vacuum line
directly to the Dukes valve. I am planning on using a check valve from
McMasters - $2.90.
It was concluded that the engine will
provide sufficient vacuum until the throttle is pushed in for take off.
The check valve will hold the vacuum and Dukes valve open until the valve
control system takes over.
The logistics of several approaches were gone
over with Pat Patrick. He acknowledged the findings and confirms that
the manifold system should work well. Pat also acknowledged the problem
with the Venturi concept is that air has to be streaming into the cabin before
the Venturi draws a vacuum on the Dukes valve. By that time, a pressure
will build up in the cabin and the occupants will feel a pressure surge.
Alternatives were discussed, such as, using the door seal pump and a separate
pump. All the other approaches appear to require more complex or
involved procedures to get them to work properly.
One further advantage to the manifold vacuum
approach is that all the parts should be inexpensive stock items.
If anyone is interested, I will submit what
should be a short bill of materials and a simple diagram of my final system
after getting it installed. Be aware, though, it will be awhile before
this approach is put to the acid test.
Thanks for your help.
Scott Turner
FOLLOW-UP: The concept has now been
employed and it's been reported to work without a hitch. The person who
used the method said he bought a plastic fitting at an auto supply store along
with some 1/4" poly-flow tubing. For a check valve he used the same
check valve which Lancair supplies for their door seal system.
If anyone has any quesions you can call me.
215-848-4500 (day) or 215-848-6605 (evening).
Scott Turner IV-P builder -
90%/90%