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Date: Wed, 23 Mar 2011 14:04:17 -0400
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Subject: Re: [LML] Re: Pressurization
From: Colyn Case <colyncase@earthlink.net>
In-Reply-To: <list-4915943@logan.com>
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References: <list-4915943@logan.com>

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=20
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). =20

Colyn


On Mar 23, 2011, at 8:47 AM, <bronnenmeier@GROBSYSTEMS.COM> =
<bronnenmeier@GROBSYSTEMS.COM> wrote:

> Dear Pete/Group,
>=20
> 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.
>=20
> This is what I found out/wired mine - please advise if I am wrong:
>=20
> Pin 4 and 13 on the outflow valve are doing the same thing - if they =
get
> grounded the system will dump the cabin pressure
>=20
> I used pin 4 for the airspeed/valve handle circuit.
>=20
> I used pin 13 for the electrical manual dump switch.
>=20
> 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=20
>=20
> The wiring diagram for pin 13 is correct - pin 13 is grounded when the
> switch is closed.
>=20
> 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
>=20
> I hooked up my outflow valve to my vacuum pump circuit that I use for =
my
> steam instrument gages (gyro etc.)
>=20
> Thanks for your help
>=20
> Ralf=20
>=20
>=20
> -----Original Message-----
> From: Pete Sinclair [mailto:pete@leapfrogventures.com]=20
> Sent: Tuesday, March 22, 2011 9:01 AM
> To: lml@lancaironline.net
> Subject: RE: Pressurization
>=20
> 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.
>=20
> Pin 13 goes to a second solenoid in the pressure head, but I have yet =
to
> figure out what it does.
>=20
> Pete
>=20
> -----Original Message-----
> From: billhogarty [mailto:billhogarty@hughes.net]=20
> Sent: Sunday, March 20, 2011 6:29 AM
> To:=20
> Subject: Pressurization
>=20
> For Pete Sinclair:
>=20
> 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
>=20
> gear down switch.   Any help here??
>=20
> Thanks, Bill Hogarty
> <pressurisation 1.pdf><pressurisation.pdf>--
> For archives and unsub =
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