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Date: Sun, 10 Mar 2013 10:11:51 -0400
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From: "pete@leapfrogventures.com" <pete@leapfrogventures.com>
Subject: RE: Pressurization
Thread-Topic: Pressurization
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John,

I assume you are adding a cabin altimeter to your instrument panel?  It rea=
ds out both the cabin differential in psi and the cabin altitude.  It is a =
must have IMHO to monitor and prevent cabin over-pressurization.  It is the=
 only test instrument needed for calibrating the Dukes and sealing the cabi=
n.

I know that there is an overpressure valve that mounts next to the Dukes.  =
However, my Dukes head was not working properly during testing and was not =
opening.  The overpressure valve was no match for the amount of pressurized=
 air coming in the cabin, and the pressure quickly went over 6.5 psi before=
 I was able to do a manual dump.  If you look at the teeny size of the over=
pressure valve and compare that to the volume of pressurized air coming int=
o the cabin on climb-out, you will quickly come to the conclusion that it p=
rovides inadequate over pressurization protection.

I think you are using a G900 like me.  It has an annunciator input called C=
ABIN ALTITUDE.  I connected that annunciator to a pressure switch set to 6 =
psi that compares the pressure in the cabin to the pressure under the floor=
 in the baggage compartment (where the switch is mounted).  In case the Duk=
es valve fails and the cabin pressure rises too high, at least I will get s=
ome notice (see note above about not depending on the manual vent valve).

I do have a digital differential manometer that measures PSI you are welcom=
e to borrow.  I used it to calibrate the overpressure valve that mounts nex=
t to the Dukes (I set it to 6psi).  I built a plenum from a large plastic f=
ood container that you can pressurize with a compressor (carefully) that yo=
u can borrow as well.

Pete

From: John Barrett [mailto:jbarrett@carbinge.com]
Sent: Friday, March 08, 2013 5:11 AM
To: lml@lancaironline.net
Subject: Pressurization

I didn't think I'd need help with measurement issues, but I'm hitting some =
stone walls.

I have a pocket altimeter I thought I'd use but wonder if it will have a st=
op on negative altitude.  Also I went online to see how to convert altitude=
 differential to PSID.  Not much luck.  The one site I found had conversion=
 formulae that don't seem correct.  It lists a correlation 1" of mercury to=
 1,000 feet of altitude and that should be ok.  It then goes on to list a .=
49 conversion factor to get from inches of mercury to psi.

My calculations show that at a service ceiling of FL290 the altitude differ=
ence to 10,000 foot cabin alt is 19,000 feet.  .49 times this difference is=
 about 9.5 PSID.  That's WAY higher than the 5.0 PSI we're supposed to be s=
eeing in the LIVP at FL 290.  I had hoped to test to about 6 PSI.

Short of an altimeter that allows negative readings all the way to somethin=
g over 19K and a formula that works, the only other instrument I can think =
of is a gauge that reads psi.  I found some online that sell for from a cou=
ple hundred bucks to $450 or so.  They all appeared to be set up for plumbi=
ng into a pipe system and I don't know if they would read correctly if plac=
ed inside the cockpit.

How have you IVP builders out there gone about getting measurements when se=
aling up the pressure vessel?

Thanks,

John Barrett, CEO
Leading Edge Composites
PO Box 428
Port Hadlock, WA 98339

www.carbinge.com<http://www.carbinge.com>


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<o:idmap v:ext=3D"edit" data=3D"1" />
</o:shapelayout></xml><![endif]--></head><body lang=3DEN-US link=3Dblue vli=
nk=3Dpurple><div class=3DWordSection1><p class=3DMsoNormal><span style=3D'c=
olor:#1F497D'>John,<o:p></o:p></span></p><p class=3DMsoNormal><span style=
=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span s=
tyle=3D'color:#1F497D'>I assume you are adding a cabin altimeter to your in=
strument panel?&nbsp; It reads out both the cabin differential in psi and t=
he cabin altitude.&nbsp; It is a must have IMHO to monitor and prevent cabi=
n over-pressurization.&nbsp; It is the only test instrument needed for cali=
brating the Dukes and sealing the cabin.<o:p></o:p></span></p><p class=3DMs=
oNormal><span style=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=
=3DMsoNormal><span style=3D'color:#1F497D'>I know that there is an overpres=
sure valve that mounts next to the Dukes.&nbsp; However, my Dukes head was =
not working properly during testing and was not opening.&nbsp; The overpres=
sure valve was no match for the amount of pressurized air coming in the cab=
in, and the pressure quickly went over 6.5 psi before I was able to do a ma=
nual dump.&nbsp; If you look at the teeny size of the overpressure valve an=
d compare that to the volume of pressurized air coming into the cabin on cl=
imb-out, you will quickly come to the conclusion that it provides inadequat=
e over pressurization protection.<o:p></o:p></span></p><p class=3DMsoNormal=
><span style=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNo=
rmal><span style=3D'color:#1F497D'>I think you are using a G900 like me.&nb=
sp; It has an annunciator input called CABIN ALTITUDE.&nbsp; I connected th=
at annunciator to a pressure switch set to 6 psi that compares the pressure=
 in the cabin to the pressure under the floor in the baggage compartment (w=
here the switch is mounted).&nbsp; In case the Dukes valve fails and the ca=
bin pressure rises too high, at least I will get some notice (see note abov=
e about not depending on the manual vent valve).<o:p></o:p></span></p><p cl=
ass=3DMsoNormal><span style=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p><=
p class=3DMsoNormal><span style=3D'color:#1F497D'>I do have a digital diffe=
rential manometer that measures PSI you are welcome to borrow.&nbsp; I used=
 it to calibrate the overpressure valve that mounts next to the Dukes (I se=
t it to 6psi).&nbsp; I built a plenum from a large plastic food container t=
hat you can pressurize with a compressor (carefully) that you can borrow as=
 well.<o:p></o:p></span></p><p class=3DMsoNormal><span style=3D'color:#1F49=
7D'><o:p>&nbsp;</o:p></span></p><div><p class=3DMsoNormal><span style=3D'co=
lor:#1F497D'>Pete<o:p></o:p></span></p></div><p class=3DMsoNormal><span sty=
le=3D'color:#1F497D'><o:p>&nbsp;</o:p></span></p><div><div style=3D'border:=
none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=3DM=
soNormal><b><span style=3D'font-size:10.0pt;font-family:"Tahoma","sans-seri=
f"'>From:</span></b><span style=3D'font-size:10.0pt;font-family:"Tahoma","s=
ans-serif"'> John Barrett [mailto:jbarrett@carbinge.com] <br><b>Sent:</b> F=
riday, March 08, 2013 5:11 AM<br><b>To:</b> lml@lancaironline.net<br><b>Sub=
ject:</b> Pressurization<o:p></o:p></span></p></div></div><p class=3DMsoNor=
mal><o:p>&nbsp;</o:p></p><p class=3DMsoNormal>I didn&#8217;t think I&#8217;=
d need help with measurement issues, but I&#8217;m hitting some stone walls=
.<o:p></o:p></p><p class=3DMsoNormal><o:p>&nbsp;</o:p></p><p class=3DMsoNor=
mal>I have a pocket altimeter I thought I&#8217;d use but wonder if it will=
 have a stop on negative altitude.&nbsp; Also I went online to see how to c=
onvert altitude differential to PSID.&nbsp; Not much luck.&nbsp; The one si=
te I found had conversion formulae that don&#8217;t seem correct.&nbsp; It =
lists a correlation 1&#8221; of mercury to 1,000 feet of altitude and that =
should be ok.&nbsp; It then goes on to list a .49 conversion factor to get =
from inches of mercury to psi.&nbsp; <o:p></o:p></p><p class=3DMsoNormal><o=
:p>&nbsp;</o:p></p><p class=3DMsoNormal>My calculations show that at a serv=
ice ceiling of FL290 the altitude difference to 10,000 foot cabin alt is 19=
,000 feet.&nbsp; .49 times this difference is about 9.5 PSID.&nbsp; That&#8=
217;s WAY higher than the 5.0 PSI we&#8217;re supposed to be seeing in the =
LIVP at FL 290.&nbsp; I had hoped to test to about 6 PSI.<o:p></o:p></p><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p><p class=3DMsoNormal>Short of an alt=
imeter that allows negative readings all the way to something over 19K and =
a formula that works, the only other instrument I can think of is a gauge t=
hat reads psi.&nbsp; I found some online that sell for from a couple hundre=
d bucks to $450 or so.&nbsp; They all appeared to be set up for plumbing in=
to a pipe system and I don&#8217;t know if they would read correctly if pla=
ced inside the cockpit. <o:p></o:p></p><p class=3DMsoNormal><o:p>&nbsp;</o:=
p></p><p class=3DMsoNormal>How have you IVP builders out there gone about g=
etting measurements when sealing up the pressure vessel?<o:p></o:p></p><p c=
lass=3DMsoNormal><o:p>&nbsp;</o:p></p><p class=3DMsoNormal>Thanks,<o:p></o:=
p></p><p class=3DMsoNormal><o:p>&nbsp;</o:p></p><p class=3DMsoNormal>John B=
arrett, CEO<o:p></o:p></p><p class=3DMsoNormal>Leading Edge Composites<o:p>=
</o:p></p><p class=3DMsoNormal>PO Box 428<o:p></o:p></p><p class=3DMsoNorma=
l>Port Hadlock, WA 98339<o:p></o:p></p><p class=3DMsoNormal><o:p>&nbsp;</o:=
p></p><p class=3DMsoNormal><a href=3D"http://www.carbinge.com">www.carbinge=
.com</a><o:p></o:p></p><p class=3DMsoNormal><o:p>&nbsp;</o:p></p></div></bo=
dy></html>=

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