Transportation Services Consulting, Inc. - Professional Services for the Lancair Builder  

Transportation Services Consulting

Professional Services for the Lancair Builder

HOW TO TEST PRESSURIZATION

We make a few assumptions before we begin this test. They are, the Turbos are spinning at the proper speed and providing a full 31.5 in. at 2400 rpm up to 24,000 feet. This will insure that there is sufficient volume available to pressurize the cabin. Check all hoses from the intercoolers to the mix valve for rub holes, good clamps, etc. etc. Use Skeet (2 ply) vs. Scat hose.

Given the fact that we have sufficient volume and air pressure available at the mix valve, we can check the downstream side from the mix valve.

The way to approach the subject is to eliminate the elements that could be leaking. I'll give you a list that if you check off each one, by the time you get to the end you should have it fixed.

If your A&P has a large capacity air compressor that will be a great help. An alternate pressurization device could be a large capacity shop vacuum connected to the blow side. I use a 6hp Sears shopvac.

First---Check the outflow valve. Electrically and mechanically.

Remove the outflow valve and check the electrical canon plug against the wiring diagram. Especially check the dump switch and the gear handle microswitch. Turning off the door seal will depressurize faster than any dump switch!

Connect the electrical canon plug.

With power on, operate the pressurization controller to both upscale and down scale positions.

The outflow should open and close and fit snugly against the seat. The bladder will not be extended but you should be able to determine if the center collar is that the end of the shaft.

Reinstall the valve and make the absolutely certain that the nose cone of the pressurization valve is free and clear of all lines fittings etc. etc. under the bucket. I had this problem and it drove me crazy. Use silicone around the bottom of the valve itself to seal into the bucket.

Check the filter on the outflow valve for cleanliness.

I also would remove the vacuum source line and cap it. I do not believe it does any good and will be a problem source down the road. I put my controller to the highest range as soon as I descend below 5000 feet. This puts the outflow valve open and stops the rattle of my NACA scoop air inlet valve on the pressure bulkhead. And allows full airflow in from the NACA scoop for cooling. I then close off the engine air inlet (which puts all engine bleed air overboard). All this is assuming no Air Conditioning.

For takeoff I have maximum ventilation until I climbed airplane to 8000 feet (approximately) I roll the altitude selector down to 8000 feet and open the engine air valve slowly. This keeps a cabin cool, (as possible) and I have less ear problems.

Remove the static source aluminum line and cap the portion that goes overboard. This allows the cabin pressure to force the outflow valve closed. If there's any doubt that the outflow valve is not operating properly put a plate over the bucket and seal that.

Remove the control wire from the master relay.

Check for leaks

Check the mix valve to have adequate tension on the temperature disk that rotates (controls hot vs. cold source air) (pre intercooler vs. post air cooler air). Boy if that isn't a joke! Both are hot. Disconnect both inlets. Put your finger in the holes and make sure the disk is in the proper position related to the cable handle connection (and labeled properly). Make sure or shaft has a spring and it is tightened down so that coils will barely allow a business card between them.

Prepare the interior

Instant glue a nylon thread to the bat (handle) of the door seal switch. Run the thread out the door and tape it into position so that pulling on the thread can deflate (turn off) the door seal.

Turn on door seal switch.

Check the outflow valve static port (aluminum line) is opened to atmosphere--and the outside port is capped.

Also remove and cap the pressure port to the elevator compensator. (You may want to connect this to an exterior gauge).

Check the over pressure valve is tightened and installed in the proper direction. If in doubt-- put a piece of tape over it.

Turn on the master switch.

Prepare the exterior

Close and latch door handles.

Connect master switch control wire to relay. Door seal should pump up. Connect vacuum cleaner or air compressor and start pressurization. A mechanic's stethoscope will help. A microphone on a wand with that a headset to listen is also very useful.

Vacuum cleaner should give over 2 psid. Air compressor ovthaner 4 psid. Look in the window at the differential pressure gauge. Or---connect an extension hose to the elevator compensator line and connect your own pressure gauge. The 0-10 psi range would be correct.

To check for air leaks:

Put your hand around the door. Check the door seal for leaks. And check around the door handles. Lock (not much you can do about this one).

Check the firewall.

Especially check the overboard dump valve (adjustment) (1 in. line) coming from the left side of the mix valve.

Minor leaks from the throttle- prop- mixture cables are okay.

Leaks around wiring hydraulic fittings fuel fittings etc. should be sealed.

Remove the lower fuel line access plate at the wing root. Check for leaks of around fittings (pitot, nav-antenna etc.) and wiring pass-throughs. Check around the aileron boots.

Open the gear doors and check side skirts and seat bottom. Check for outflow valve leaks and interference.

Check elevator boots.

Check around safety belt pass through cutouts. This is a common leak source.

Disconnect and check for air passing into the fresh air inlet door in the upper center of the pressure bulkhead.

You can probably think of a few other places to check.

When finished--- disconnect the master switch relay control wire.

Pull thread that is connected to the door seal switch. The seal should deflate. If it pulls off or becomes disconnected for some reason, take the rest of the day off and come back tomorrow. It will take that long for the seal to deflate on its own. Don't try to force door open with seal inflated.

Once you have exhausted your ability to find leaks from the outside, have someone sit inside the cabin with the seats, and sidewalls removed. Pressurize -- and try a smoke source around the potential leak areas.

To seal difficult areas, I coated fiberglass cloth material on both sides with silicone (wet) and used it to seal around areas such as safety belt and hardware etc. etc.

For all other areas, I used the straight GE clear silicone from Wal-Mart.