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I talked to Carlos at Dukes for quite a while yesterday.
As well as I could piece together:
The main valve is moved by a diaphragm.
How far open or closed the valve is, is determined by what pressure is allowed to enter the diaphragm chamber
A small orifice from the chamber to ambient is always present, which, in the absence of any other air source will tend to equalize pressure on each side of the diaphagm.
When high pressure cabin air is allowed in, the valve closes. When ambient air is allowed in, the valve opens enough to reduce the pressure differential to almost zero. When vacuum is connected, it opens all the way.
Pin 13 controls a solenoid in the valve that connects ambient air to the chamber. This results in near equalization to ambient but the valve is not open far enough to avoid the pressure wave you can get on takeoff.
Pin 4 controls a solenoid that connects the vacuum port to the chamber. When this is energized the valve opens completely. (This avoids the pressure wave when the turbo first spools up.) If you care, the cross-section of the fully open valve is 9.5 square inches (I care because I'm trying to improve my non-pressurized fresh air flow).
The Lancair picture is graphically correct but it doesn't distinguish in name between the dump solenoid and the vac solenoid.
As Pete described, inside the valve is a movable aneroid which is connected to a poppet. The position of the aneroid corresponds to the target pressure delta. There's a motor which moves the aneroid and a pot that reports the position. The controller energizes the motor until it sees the position indication it's looking for. The RATE knob controls how fast the motor turns. This means that if the controller loses power, the aneroid is where it is, and the valve continues to operate at the latest pressure differential target.
If you wanted to maximize exit airflow when flying unpressurized, you would want to have a vacuum source and energize pin 4 until you want to pressurize. (If you do this, be careful where you have the cabin altitude target when you de-energize the vac solenoid).
Colyn
On Mar 23, 2011, at 8:47 AM, <bronnenmeier@GROBSYSTEMS.COM> <bronnenmeier@GROBSYSTEMS.COM> wrote:
> Dear Pete/Group,
>
> I rewired my pressurization - I am somewhat not able to test the system
> completely on the ground (which I was told is not uncommon). I hopefully
> fly soon - then I should know.
>
> This is what I found out/wired mine - please advise if I am wrong:
>
> Pin 4 and 13 on the outflow valve are doing the same thing - if they get
> grounded the system will dump the cabin pressure
>
> I used pin 4 for the airspeed/valve handle circuit.
>
> I used pin 13 for the electrical manual dump switch.
>
> The wiring diagram for pin 4 can only be used as a schematic - the logic
> is wrong - the lancair manual shows it right: pin 4 is grounded when
> airspeed is low AND the gear handle is down
>
> The wiring diagram for pin 13 is correct - pin 13 is grounded when the
> switch is closed.
>
> I used the pin 13 as an ON/OFF switch for my pressurization and mounted
> the switch up side down - I turn on the pressurization when I open the
> switch
>
> I hooked up my outflow valve to my vacuum pump circuit that I use for my
> steam instrument gages (gyro etc.)
>
> Thanks for your help
>
> Ralf
>
>
> -----Original Message-----
> From: Pete Sinclair [mailto:pete@leapfrogventures.com]
> Sent: Tuesday, March 22, 2011 9:01 AM
> To: lml@lancaironline.net
> Subject: RE: Pressurization
>
> The wiring diagrams I have seen show the gear switch grounding pin 4 of
> the pressure head for planes without vacuum, and pin 13 if you have
> vacuum. I think this is backwards. Pin 4 opens a solenoid in the
> pressure head that connects the vacuum port directly to the bellows.
> This allows the vacuum to pull the bellows fully open (dump mode). So,
> if you have vacuum, you want pin 4 grounded when on the ground and
> taking off (to prevent the pop you get when going to full power). I
> added a small electric vacuum pump to mine to do this that goes on
> whenever pin 4 is grounded.
>
> Pin 13 goes to a second solenoid in the pressure head, but I have yet to
> figure out what it does.
>
> Pete
>
> -----Original Message-----
> From: billhogarty [mailto:billhogarty@hughes.net]
> Sent: Sunday, March 20, 2011 6:29 AM
> To:
> Subject: Pressurization
>
> For Pete Sinclair:
>
> Pete: Looks like you might be the expert on this topic. I was looking
> for a preflight check but thought that the system was grounded thru the
>
> gear down switch. Any help here??
>
> Thanks, Bill Hogarty
> <pressurisation 1.pdf><pressurisation.pdf>--
> For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
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