I was having trouble getting above about 3.5 psid. I found that my dump
valve (in the mixing box mounted on the firewall) was not completely
closing. You can put eyes on this by removing both the "cold" and "hot" feed
lines to the mixing box and peering inside with a flashlight. It was a
simple cable adjustment to correct. I can now get to about 4.8 psid. That is
probably as good as it gets until I spend some time chasing leaks in the
cabin.

At the same time I discovered the hot/cold valve was loose (the nut and
spring on the forward side of the mixing box) so that even when set to
"cold" only it was letting a lot of hot air into the cabin more-or-less
neutralizing the effect of the air conditioner.

Jay Phillips

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of John
Barrett
Sent: Wednesday, September 04, 2013 4:42 AM
To: lml@lancaironline.net
Subject: [LML] IVP pressurization

Having trouble getting my pressurization to work effectively.
I did my best to seal the pressure vessel but never got above .25 PSID with
my 6 horse shop vac.  Used both pressure and vacuum to check for leaks.  No
smoke but used a down feather and then a stethoscope with tympanic membrane
removed.  Outflow valve is covered during these tests.

After lots of frustration i hired a guy who has built and/or pressurized
about a dozen IVPs to come take a look.  He determined using smoke that
there were a couple of slight improvements to be made mostly in the wire
bundles through the aft pressure bulkhead and after doing this he declared
the vessel seal very good.  

So we deduced that maybe the shop vac is not as efficient at blowing air as
I thought, but my flying experience with the aircraft is that it doesn't do
much better than the .25 PSID in flight up to 14.5K ft.  

Wondering why there is inadequate pressurization with a good pressure vessel
leads to thoughts of outflow valve problems.  I bought the device with the
kit in 1996 so it occurs to me the valve could be dirty or rubber diaphragm
could be failing, etc.  I removed the outflow valve yesterday and tried to
examine the parts.  i lubricated the mandrel that the poppet valve slides on
with a very small spritz of LPS1 lubricant in case there was stiction there.
I did notice that with the poppet valve manually moved to the furthest
closed position the diaphragm still had somewhere around a 1/32" gap at the
seating perimeters.  Should the air pressure in flight fill that diaphragm
to close the gap or does this indicate the valve needs servicing?

Finally is there a way short of the manual dump switch to keep the system
from pressurizing better than what I see by mismanaging the controller?  Am
I just setting the pressurization up  wrong?  Have only been up to 3,000 ft
elevation airports, (KRDM) and lower - most at sea level.

Thanks for any help.

John Barrett

Sent from my iPad
 
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