| Hi John,
I fabricated a wedge from scraps which held the controller full closed with slight tension. This allows you to confirm the tub and controller seals are solid.The controller manufacturer confirmed this was good practice. If you use two shop vacs (one blowing into the next) you will generate sufficient pressure to both hear and feel any leaks from inside and outside the cabin. It is also important to have someone on the outside listen and feel for leaks as well. Prop the gear doors open and have the outside person stick his head in each gear well. Be sure to remove the wedge before doing any flying.
You should be able to hear the controller motor run when you change the cabin altitude setting to insure it is wired properly. The controller is very reliable so it would be the last thing I would suspect.
With the controller set 3,000 feet above the airport you should be able to feel substantial warm air blowing from the vents at pattern altitude and cruise power. The air should get hot when you change the mixing valve setting from the coldest to a bit warmer.
With the the controller set 1,000 feet above the airport the cabin should climb right up to 4.5 psi as you climb and then remain at 4.5 psi as you climb further.
Hope the above helps. Send an email if you want to discuss further. It took me a few tries to really get it right.
Jack Morgan On Sep 5, 2013, at 6:01 AM, Lancair Mailing List wrote: Subject: IVP pressurization
Date: September 4, 2013 7:42:10 AM EDT
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
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