Nope. No vacuum is necessary to run the Dukes. The only purpose for the vacuum connection is to pull the bellows open when pin 4 is grounded.
The Dukes head operates on the pressure differential between outside and cabin pressure. It is effectively powered by the pressurized air coming into the cabin. The pressure head only uses electricity to operate the solenoid connected to pin 4 (and a second solenoid connected to pin 13) and for a motor that moves a bleed valve in concert with the position of the cabin pressure control on the dash. When pin 4 and pin 13 are not grounded, the vacuum connection is completely sealed off from the pressure head.
It truly is a mechanical marvel when operating properly.
Pete
From: Paul Miller [mailto:pjdmiller@gmail.com]
Sent: Monday, October 14, 2013 5:14 AM
To: lml@lancaironline.net
Subject: Re: [LML] Re: Removing vacuum pump? (LIVP)
If the pressure controller on the panel has rate of climb and cabin altitude settings (like a Garrett), it likely uses the vacuum line to modulate the outflow valves (pull them open). That modulation is what provides the signal to allow the cabin to climb or descend. I don't know what controller is in place but the vacuum is for cabin differential control. The squat switch is for ground use or emergency and simple opens the outflow to a maximum. In a typical situation, the outflow closes with wheels up then the vacuum signal starts to open the valves to provide the differential required to either climb or hold the cabin as set by the controller.
If the vacuum is disconnected, I suspect you simply are running with a fully closed outflow valve and the cabin pressure is an open loop with whatever pressure is supplied from the firewall. Does that sound about right?
What I am missing is if there is no vacuum line then why install the controller? How does it control anything? Those controllers can't be cheap.
On 12 October 2013 17:00, jeffrey liegner <liegner@ptd.net> wrote:
The device might function better (although I can't prove that), but it is not necessary. I recall that it is to help the valve move initially (and has no value after that first movement) and effect a seal early