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 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 difference 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 seeing 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 something 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 couple hundred bucks to $450 or so.  They all appeared to be set up for plumbing into a pipe system and I don’t know if they would read correctly if placed inside the cockpit.

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

Thanks,

John Barrett, CEO

Leading Edge Composites

PO Box 428

Port Hadlock, WA 98339

www.carbinge.com