When I pressure tested my IV-P prior to first flight I used my 10Hp shop compressor which has a 200 gallon tank. The outflow valve was plugged as were all the other ports into the cabin except a 1/2 " port for connecting the compressor, a 1/4" port for a pressure gage and the door seal pressurization line. I connected the airplane to the compressor with a 3/8" commercial air hose.

The procedure was to close the door, pressurize the door seal and then connect the air line. One person monitors the cabin pressure with an ACCURATE low pressure gage (0-10 or 0-15 PSI) while others scramble around identifying leaks. IT IS ESSENTIAL that the gage line is NOT "T"ed into the supply line. Use a separate pressure penetration. A big tank on the air compressor is helpful as it gives you more time to find the leaks. Venting the door seal will quickly depressurize the cabin (and clean half the hanger).

Have fresh underwear on hand as the airframe will make some startling noises when it is first pressurized. It will also change shape as it tries to turn into a sphere. 5 PSI is about what is in a basketball, you get the picture.

After about a day of work I was able to get the cabin up to 7.5 PSI for about a minute before the air compressor tank ran low. Lancair recommends 6.5 PSI but I decided that a test to 1.5 times rated was required for my personal comfort. I also know of 4 builders who have had structural failures of the aft pressure bulkhead during testing. Better in the hanger than in flight.

It is important to have a well sealed cabin in order for the outflow valve to function properly. If the cabin has a lot of leaks then the outflow valve is almost or completely closed in high altitude flight and it has little control over the cabin pressure and your ears will suffer. If the cabin is well sealed the outflow valve has good authority over the cabin pressure and can make smooth, comfortable changes as required.

Under no circumstances should you operate your airplane at a cabin pressure higher than it was tested at on the ground. If you don't have a big enough compressor then rent one. There is absolutely no reason to risk life and limb in a flight test when the same test can be conducted on the ground for a modest investment in time and money. This is true for all the systems on your airplane.

Regards
Brent Regan