A report on LIVP pressurization efforts...

I recently began the effort to get a 5.0 psi cabin pressure differential.  Having flown for five months with no PSI differential on the UMA guage supplied with the kit, it was time.

Importantly, I did this by myself, from within the airplane, using a ShopVac.

First, I sealed over the Duke's Valve opening with duct tape.  Use extra duct tape so it holds. You must remove it from the equation, since the squat switch feature leaves it open on the ground.

I uncowled the top, removed the cold turbo air input into the mixing box and replaced it with SCAT tube connected via duct tape to my ShopVac hose.  For the details, I simply wrapped tape around the SCAT end until it fit snugly into the ShopVac attachment, and secured it with more tape.

I then put the ShopVac on suction, got inside, closed the door and inflated the door seal.  I could then hunt for leaks using my hand, my ears and a peacock feather.  I found leaks around the aileron bell crank leading out into the wings (tie wraps not tight), along the edge of the back seat where it overlies the gear box, with half of the wire bundles penetrating the rear bulkhead area, the tight corner area behind the elevator push rod where the penetrate the aft bulkhead (there's the tiny corner which was difficult to fully epoxy with BID), small wire holes coming in from the wing root, coming in from rear area, and two coming through the firewall.

Once the leaks were identified, I would exit, reverse the ShopVac, placing it on blow, and return to the cabin, seal the door, and apply sealant to the leaks previously identified.  I sealed these small openings with HomeDepot clear silicone dispensed from a chaulking gun (purists will cringe).  The ShopVac pressure encouraged the silicone deeper into the gap.

Letting this silicone dry for a day, I would return and repeat the process.

Lesson #1: there are more leaks then you think, and it takes four or five generations of sealing and dry time (>day) to get them.  You first find the big ones and seal them.  Next you find the medium size ones and seal them.  And towards the end you are finding tiny leaks, which you seal.  It was not until the tiny ones got sealed that I showed any PSI differential from the ShopVac's blowing effort.

Lesson #2: Cannon plugs (or AMP or whatever), unless they are "sealed" and have no unused connector slots, leak A LOT MORE than you think.  Fortunately, there are rubber "plugs" that you can buy (~20 cents each) from the company that insert perfectly into the empty slots and effectively seal the leak.  Six unused slots on a cannon plug is like a dime-size hole in the firewall.

Lesson #3: Sealing leaks with ShopVac pressure may force more silicone into the gap than you need to, so apply silicone and then stop the ShopVAc, or you will be replacing silicone blown deeper in the hole with more and more silicone.

Lesson #4: Getting no pressure differential on the guage early is not a guage problem.  Getting 0.5 PSI on the guage is a VERY GOOD sign that your are making progress, and occurred at the fourth generation.  Getting 1.0 PSI differential out of a standard ShopVac is all you can hope for from its small motor, and you are close to completion.  And finally, when you exit the cabin after the fifth generation of leaks and you detect that funny electrical smell from the ShopVac's motor pulling on a vacuum, you have the olefactory confirmation that you are ready to flight test the cabin.

Lesson #5: I did not need a large compressor or a pressurization consultant or a sonic stethoscope to complete this task.  Yeah.

During my first flight, I punctured a hole in the previously applied duct tape overlying the Duke's Valve, so I could return the Duke's into some service to control pressure, and with one finger I could monitor air flow through the puncture.  Satisfied that the valve was working during the flight test, I peeled back more duct tape until there was a plenty big opening.

During climb out, I very quickly had 3 PSI cabin differential at 31.5" MAP.  Climbing through 10,000' (29.7"MAP 2500RPM 17.8GPH 60*F LOP) I had 4 PSI differential and 1000' cabin.  At 13,000', 5 PSI differential and 1250' cabin.  At 16,000', 5 PSI differential and 3300' cabin (and I had pulled back to 27" MAP).  At 17,500' level cruise, I had 5 PSI differential, a 4300' cabin, and I could maintain 5 PSI differential down to 25.8" MAP, at which point I showed 176 IAS and 238 TAS.

That's my report.  I thought I'd share.

Jeff Liegner

N334P