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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
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