X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 10 Mar 2013 10:11:51 -0400 Message-ID: X-Original-Return-Path: Received: from p3plex2out04.prod.phx3.secureserver.net ([184.168.131.18] verified) by logan.com (CommuniGate Pro SMTP 6.0.2) with ESMTP id 6113452 for lml@lancaironline.net; Sat, 09 Mar 2013 12:20:12 -0500 Received-SPF: none receiver=logan.com; client-ip=184.168.131.18; envelope-from=pete@leapfrogventures.com Received: from P3PW5EX1HT003.EX1.SECURESERVER.NET ([72.167.180.21]) by p3plex2out04.prod.phx3.secureserver.net with secureserver.net id 9VKc1l0010U5vnL01VKc8S; Sat, 09 Mar 2013 10:19:36 -0700 Received: from P3PW5EX1MB14.EX1.SECURESERVER.NET ([10.6.135.86]) by P3PW5EX1HT003.EX1.SECURESERVER.NET ([72.167.180.21]) with mapi; Sat, 9 Mar 2013 10:19:36 -0700 From: "pete@leapfrogventures.com" X-Original-To: John Barrett , "lml@lancaironline.net" X-Original-Date: Sat, 9 Mar 2013 10:18:48 -0700 Subject: RE: Pressurization Thread-Topic: Pressurization Thread-Index: Ac4ctUaKljOvlisGRTmosjKiZ5BsUgAM4BGQ X-Original-Message-ID: <2A14E6258A8534418F5498D73CCA51EF2243E99368@P3PW5EX1MB14.EX1.SECURESERVER.NET> References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: multipart/alternative; boundary="_000_2A14E6258A8534418F5498D73CCA51EF2243E99368P3PW5EX1MB14E_" MIME-Version: 1.0 --_000_2A14E6258A8534418F5498D73CCA51EF2243E99368P3PW5EX1MB14E_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable 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 --_000_2A14E6258A8534418F5498D73CCA51EF2243E99368P3PW5EX1MB14E_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

John,

 

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

 

I know that there is an overpres= sure valve that mounts next to the Dukes.  However, my Dukes head was = not working properly during testing and was not opening.  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.  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.

 

I think you are using a G900 like me.&nb= sp; It has an annunciator input called CABIN ALTITUDE.  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).  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).

 

<= p class=3DMsoNormal>I do have a digital diffe= rential manometer that measures PSI you are welcome to borrow.  I used= it to calibrate the overpressure valve that mounts next to the Dukes (I se= t it to 6psi).  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.

 

Pete

 

From: John Barrett [mailto:jbarrett@carbinge.com]
Sent: F= riday, March 08, 2013 5:11 AM
To: lml@lancaironline.net
Sub= ject: 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 stop on negative altitude.  Also I went online to see how to c= onvert altitude differential to PSID.  Not much luck.  The one si= te 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 serv= ice ceiling of FL290 the altitude difference to 10,000 foot cabin alt is 19= ,000 feet.  .49 times this difference is about 9.5 PSID.  That= 217;s WAY higher than the 5.0 PSI we’re supposed to be seeing in the = LIVP at FL 290.  I had hoped to test to about 6 PSI.

 

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.  I found some online that sell for from a couple hundre= d bucks to $450 or so.  They all appeared to be set up for plumbing in= to a pipe system and I don’t know if they would read correctly if pla= ced inside the cockpit.

 

How have you IVP builders out there gone about g= etting measurements when sealing up the pressure vessel?

 

Thanks,

 

John B= arrett, CEO

Leading Edge Composites=

PO Box 428

Port Hadlock, WA 98339

 

www.carbinge= .com

 

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