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  #1  
Unread 06-07-02, 12:56 AM
Alan Williams Alan Williams is offline
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Pressurization

My 337 was a cloud seeder in the Middle east till last August. Read work /farm aircraft. A winter of overhaul and new gadgets has everything working but the pressurization. New cessna door seal, storm windows sealed, avionics bay cover tight, nosewhell steering boot replaced, generally prc d all the holes. Presure differential gauge barely comes off the peg giving about 1500 ft cabin actual diferential up to 15,000 ft.
What are the other common places or things to look at.
Help greatly appreciated.
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  #2  
Unread 06-07-02, 01:30 AM
kevin kevin is offline
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Is your outflow valve closing all the way? Can you pressurize the cabin on the ground (with external equipment)? If the controller is not closing the valve, you could have the tightest cabin in the world, but no pressurization. There is also an emergency outflow valve that could be stuck open...

How is the MP on your engines, at surface and at altitude? You should be able to get 37" (35" on some intercooled airplanes) on takeoff. At 20K, you should be able to pull 27" at 2450-2500 RPM (but not at lower RPM, regardless of what book says). If your turbos are not boosting, your pressurization will be weak as well...

Have you checked your dump valves (two handles on the right of center console, below instrument panel)?

The controllers themselves are usually very reliable, but I suppose you could have a problem there...

I am sure others more knowledgeable than me will have more to add to this...

Kevin
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  #3  
Unread 06-07-02, 08:20 AM
Bob Cook Bob Cook is offline
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pressurization

Alan

Here are some suggestions

1) can use a leaf blower and couple to the venturi or cabin inlet from upper deck. Works great. There are fittings for a ground tester, however, it is hard to find a facility with one (ground cart). The leaf blower can give you lots of air. A blower on a shop vac doesn't work well enough.............

2) look at the grommets or boots for the cables entering the cabin. These deteriorated because mechanics used GREASE or wrong form of silicon. They can cause problems. Located in base of struts and up in the wing roots. I can guarantee these are shot!

3) check around windows. Etching from repainting has caused major problems with windows leaking. Important point for new AC buyers. Warning for those that are going in for paint.

4) check all the floor panels.

5) check for leaks in upper deck (maifold). You will see them with the leaf blower if you run out of turbo boost below 15k ft.

6) make sure, as Kevin says, your turbo output is up to snuff.

7) Dirty dump valve or bad cabin controller can cause problems but you will see this with the leaf test as the system is fail save.

8) There are some "flapper" valves in the wing inlet area for fresh air that close off when pressurized. These may be sticking open.

9) Check the bulkhead feed thru's both front and rear. Loose bulkhead connectors or bad wiring installs will cause leaks. I found vacuum bulkhead connectors lose causing problems.

10) Check for items that might have been pulled out and not capped such as the fuel flow tubing or partial deice plumbing that might have been removed.

11) The turbos are different on the front and rear. Make sure they have not installed the smaller turbo on the rear. Check p/n on turbos to insure they are correct.

It doesn't take a lot to lose a lot of air at 3.3 PSI. It is the accumulated leaks that begin to add up. I can almost guarantee all the cable seals (item 2) are history. They are different sizes so be careful when you order.

you didn't give us the year or s/n as GMAS would say.......

It is a long tedeous process to tighten up P ship. I have even seen rivits leaking would you believe! As previous board member commented "there is 20 lbs of sealant in this "dude".

I am sure others will chip in.

GMAS... you have been quiet...

Bob
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  #4  
Unread 06-07-02, 04:15 PM
Mark Hislop Mark Hislop is offline
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Alan:

Along with all of the things Kevin and Bob mentioned, also check the avionics inspection panels just in front of the wind shield. They are also part of the pressure vessel. The gaskets get old and worn. Worse yet, people sometimes use silicone to try to seal them, and they get torn when you remove the panels. Also check to see that the small cups underneath each of the dzus fasteners are in place (they probably are missing). These are used to seal all of the fastener holes.

Mark
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  #5  
Unread 06-07-02, 09:48 PM
Keven
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Pressurization Worth It?

By the way, for those of you who have it or have ever had it, it seems that turbo and pressurization may not be worth all the trouble and cost of having it. Is this true for those of us who are on our first non-turbo or pressurized Skymaster? What's the cost differential a year for the perks?

Keven
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Fix Ps3

Last edited by Keven : 04-23-11 at 04:43 PM.
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  #6  
Unread 06-07-02, 11:49 PM
kevin kevin is offline
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Worth it? You ask this of a group of airplane owners? Seems a bit like asking hotrodders if they get good gas mileage...

If you live west of Kansas, I think it is VERY much worth it. Turbos make many many trips possible for me that would otherwise be scrubbed due to the combination of high tops, high MEAs and ice. You eastern guys have it much easier I am told, I guess the tops are very frequently a 8K or below during icing conditions (how would I know, I'm not going to fly someplace where it is snowing on PURPOSE, so I don't go east in the winter).

I think the speed thing is mostly a wash. You go faster westbound, but you burn more fuel coming back east at low altitude.

I have owned four normally aspirated airplaned (2 Grumman Tigers, C206 and C337) and three turbocharged airplanes (T182RG, T210, P337). I think the difference in maintenance is overblown (get it?), especially when comparing turbocharged and pressurized. Yes, turbocharged 337s (and other airplanes) do cost more to maintain. They use up more cylinders, on average, don't get to or past TBO as often, you have more exhaust system maintenance and tweaking, and once in a while you get to replace/overhaul a turbocharger. Overall, engine maintenance is on the order of 15 to 20% more expensive.

But it is WAY worth it. Especially pressurization. FL190, looking down at 16,000' tops, that's a beautiful place to be on a winter day in the west...and no cannula, no mask, no oxygen refills.

My two cents.

Kevin
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  #7  
Unread 06-08-02, 08:46 AM
Bob Cook Bob Cook is offline
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Keven / turbos

Keven

If you do serious xcountry then you want (need) to get out of the "crap". I banged around for years in a 310 and a 401b and "roughed it" a lot of the time. I wouldn't trade the p for for anything. It boils down to your profile. If you are careful and manage your engines there is no reason they won't go to tbo. For someone out learning a P is not the ship.

I totally agree with Keven. Cruising at 20k listening to the "clutter" below asking for deviations makes be glad I made the decision to go pressurized. I am too old for excitement. My wife more than appreciates the difference and i will do anything to keep her happy including putting in a new 530 so she can see where we are going <G>.

bob
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  #8  
Unread 06-08-02, 09:36 AM
Paul Sharp Paul Sharp is offline
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I wouldn't live in the west without a Turbo. I cross too many mountains for trying to eke along in a normally-aspirated version. And if you lost an engine in the noramlly-aspirated your single-engine ceilings are seriously reduced.

And what about hot/high takeoffs? I have yet to encounter a situation where density altitude was a factory with my turbo model. That isn't to say that no such situations exist because they do and you always have to be careful and check. And you always have to calculate the extra runway lengths needed due to the thinner air. But usually the problem is simply removed.

I agree with Bob that if you don't thrash the engines you should make TBO. There are some extra costs due to turbo overhauls, controller overhauls, etc. But for me they it's a required item - wouldn't be without it on one I own.
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  #9  
Unread 06-08-02, 12:18 PM
Alan Williams Alan Williams is offline
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I agree with you prssure enthusiasts.
Out here in B.C. on the very westest coast sitting on top looking down at the dark icy tops is comforting to say the least. We use our airplane for work so the advantage of being able to go in most conditions is the factor which makes the aircraft a real asset to us.
Long cross country trips Victoria - Toronto or PV are simple and easy. My comfort gauge is my sleeping family which is a good indicator of pucker factor.
Re the Garmin 530. I have a 430 and it is quite adequate to see where you are going and a breeze to use once you understand the page groups and the procedure functions. It just takes time and use to become proficient and safe. Twice , have forgotten to swith the cdi to VLOC from gps and then wondered where the glideslope was at the intercept.
In Canada MOT will not certify the installation for IFR untill a test ride with an inspector is satisfactory.
Turbo and o2 is a great idea untill you try to get it filled in unknown places. My experience was 50-80 dollars if you could find it and usually at large airports only so you also incurred landing fees as well. It is not like filling the gas tanks and I found it unworkable as a regular use item. ie, You will end up somewhere in the middle of the night wanting to be somewhere else and no O2 availible for the planned necessary altitudes. So it becomes a no-go.
Maintenace is of course more due to extra tubos but carefull operation seems to keep the cost reasonable.
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  #10  
Unread 06-08-02, 04:14 PM
kevin kevin is offline
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Echoing Alan:

Yikes, I've owned my P for too long, I forgot about high density altitude takeoffs...which shows why the Turbo/P is worth it. Taking off in Rawlins Wyoming at 2PM in the afternoon when it is 85 degrees, I guess the density altitude must be in positive controlled airspace. But no issue, not really much difference, in turbo.

I also forgot about the FEES for oxygen. I am SURE that I pay less for pressurization (not turbo) related maintenance that I used to pay for oxygen...

Kevin
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  #11  
Unread 06-08-02, 05:27 PM
Alan Williams Alan Williams is offline
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Kevin:
O2 The cost was usually outrageous and the minimal availibility just simply made it impractical for me for cross country to different unknown places.The availibility was the deciding factor.
After owning 2 turbo 337s personally I would not consider natural aspirated unless it was only for low altitude ferry sort of work. We dont seem to have much of that west of the rocks.

Gord
We were 9 hours cyyj to cns7 last week and 10.4 on the way back.
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  #12  
Unread 06-09-02, 12:22 AM
Gord Gord is offline
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Alan ,,, good you made it out east ,,, we didn't see you at Nanaimo Fly-in so presumed you headed out ,,, drew three 4's in the Poker Fly Rally and didn't even make it into the top 5 hands ,,, little less than 3 hours each way from Irma to Nanaimo and back ,,, "Slim Lizard" err Kevin was there ,, next time your P337 comes out to Alberta call ,, Gord
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  #13  
Unread 07-02-02, 12:40 AM
Alan Williams Alan Williams is offline
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Presurization

Belated greetings fellows.
Further to my pressure problem question we now have things working. It turned out in the end to be the bell in the aft controller was cracked and misshaped. of course in searching that out as it was not easily visible we found all the other little leaks. Had to replace two control cable seals and a variety of small leaks in the heat exchange system.
your list of places to look was very helpfull. We now have full differential pressure.
See s-tec autopilot thread for other interesting item.
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  #14  
Unread 07-02-02, 02:28 AM
GMAs GMAs is offline
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Smile Hmmmm..... now this is what I call a good group

Bob... you ask why I am quiet... hmmmm... I used to have a flight instructor in the service... and every time I did something wrong.. he would yell at me... then he quit... and never said another word... made me real nervious... till one day I aske him why he wasn't talking to me any more... and he said... kid... I can't teach you anything any more... ya learned and are doing it right... so unless you just want to talk about the weather... I got nothing to say...

well I guess you guys and gals have learned well... and all I have to do is sit and read... You all are begining to become the experts... as you master the aircraft and its abilities... I think it best said ... I love it when a plan comes togeather... and in this case... you all are... If you notice above each of you is adding to the whole... and learning from each other... So I don't have to really add much... you all are covering all the bases... and hitting all the high points... ya doing good... keep up the good work... this is the best board ... and growing all the time... Kevin... ya done good ... but, don't worry Bob... I won't be gone... I have other things that I will keep you on your toes with... smile... their is always more.... a whole lifetimes worth... smile... GMAs
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  #15  
Unread 07-03-02, 03:49 AM
Kevin McDole Kevin McDole is offline
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There's another seldom mentioned benefit for pressurization, even if you don't fly high. It's much easier on your ears.

I can hold sea level cabin pressure up to 7K. I once flew with a 1 year old who had a cold, and kept the cabin at sea level - no problems encountered.
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