Sealing Pressurization Leaks

[GJ Humphrey]

Can anyone recommend a first-rate shop that has the equipment and experrience in working on P337s to find and seal pressurization leaks? I need a shop that knows the P337 and has the equipment to pressurize it on the ground to 3.35.

Thanks.

[Bob Cook]

GJ

Sure picked a lengthy subject..........

What pressure does your AC hold / at what altitude ?

Can you get max differential of 3.5 ?

There are various sources of leaks. Your mechanic can use a gas powered leaf blower to pressurize the cabin on the ground to determine leaks.


Possibilities are (most likely).

1) seals around cables entries at strut roots and in wing empinage.
2) Poor door seal.
3) rivits
4) seals at bottom of cabin floor.
5) bad waste gate seal.

There have been cases where improper solvents were used when repainting causing leaks around window seals.

You need to systematically eliminate items above.

Other problems could be leaks around venturi on upper deck, seals around heat exchangers.

Later models modified the venturi's on the upper deck take-off to improve pressurization. They did make improvements over time.

Feedback on your performance can help to pinpoint problems.

suggest you make a table such as;

altitude mp rpm cabin pressure differential oat for every 1k feet up to 18k ft . You will probably need 31 inches and 2600 rpm above 14k ft to keep maintain max differential.

I spent a yr getting a '74 to meet spec. Need more info before I can become more specific.

fyi

Bob

[Dave Underwood]

Great subject! I am also working on getting my P337 to pressurize correctly and thought I would provide my two cents worth.

Here is what we have done so far: Checked the dumps, root seals and vents, windows, cabin roof, walls and cabin floor and the relief valves. Turbo pressure is good as well, at least by the manifold gauge.

I was able to get 1.9 psi a couple of weeks ago, but only that. All the leakage appear to be around the door with the worst in the corners. We then put a little Lubrication of the door seal to see if that would help. The corners don't look like they have inflated for a while. On the next flight the differential went down to 1.4 to 1.5 psi, still leaking around the door in the corners. The mystery deepens.....

Door seal is not in bad shape, but it would appear that the holes in the seal on the pressurized side were resting against the inner lip of the door frame assembly. Figure 16-20 shows you should enlarge the cutouts as required to clear the seal. On a C340 nearby, they have actually drilled a series of holes through that lip to allow the seal to inflate. We figure the lubrication just let the seal inflate enough to block the holes as was demonstrated by the lower differential and the lubrication just helped the seal. We have added a few extra holes ourselves directly over the seal holes and await better weather for another test flight.

The weather here in the UK has been really bad, but tomorrow looks good finally and I will report the result.

Any further thougths or comments would be greatfully received.

Regards - Dave

[RRossner]

Tule River Aero Ind. works on Skymasters everyday and we know all about the pressurization systems of the P337's.

If you live in or around California come see us!

Rick Rossner
Tule River Aero-Ind.

[Dave Underwood]

Flying in the UK is tough some days - today has low ceilings and RVR's with the temp and dewpoint both at +8 degees. A little foggy you might say.

The flight test went OK, with 1.9 psi attained along with slightly greater than trace icing, but we were able to confirm the boots work great. The additional holes at least allow the door seal to inflate a bit more and cut down the leaks in the corners. I suspect holes will also be required in the seal joining the top and bottom door segments as well.

On returning, we have done a "shop vac" test and guess what. Serious leaks all over the place. There will be several days spent with PRC to seal things up. That and fixing hose leaks on the front engine will keep me busy.

Surprising was the leakage through the dumps, even when we did get them to set. Anyone have any experience with those?

Regards - Dave