Did altitude just blow out 2 MPS's?, Put the in my checked baggage...now won't hold vac. Options

[rjames]

If the diaphragm isn't cracked and the seals are good, it should still hold vacuum. That doesn't speak to the condition of the cells though.

I once brought a sealed bottle of tequila with me on a flight to Japan. It was in my carry on. It was sealed with a cork that was wrapped in plastic. Halfway through the flight I reached into my carry on bag to find it soaked because the cork had lossened and broke the seal during the ascent.

[FlacaProductions]

I could use some of that tequila right now.

[JeffBowlsby]

Post photos of the front/back of the diaphragm please.

[emerygt350]

You can test if the cell is doing what it should be when you get it back together. That will tell you if it is damaged. It should still hold vacuum even if the cell is compromised. Unlikely a crack would pass through both sides. I think. You need to check that diaphragm closely for cracks, post some close up picks of it as Chris mentioned.

[JeffBowlsby]

Here's what I thought of:
The reduced atmospheric pressure resulted in expansion of the aneroid cell, which pushed the diaphragm outward, like happens during use on overrun, but with more force.

More than likely the diaphragms were close to failure already. They almost always fail at the edge of the supported perimeter area because the casting has a sharp corner there.

This^^^

An interesting dilemma. I think the aneroid cell would have expanded, pushing against both the diaphragm armature and the sliding coil armature. The diaphragm, cell and coil mail have been distorted enough to kill one of all of them, or maybe not. Each one can be tested.

[JeffBowlsby]

Here's what I thought of:
The reduced atmospheric pressure resulted in expansion of the aneroid cell, which pushed the diaphragm outward, like happens during use on overrun, but with more force.

More than likely the diaphragms were close to failure already. They almost always fail at the edge of the supported perimeter area because the casting has a sharp corner there.

This^^^

An interesting dilemma. I think the aneroid cell would have expanded, pushing against both the diaphragm armature and the sliding coil armature. The diaphragm, cell and coil may have been distorted enough to kill one of all of them, or maybe not. Each one can be tested.

https://www.engineeringtoolbox.com/docs/doc...ir_pressure.png

[FlacaProductions]

I don't see any breaches. I've held it up to a bright light to look for cracks - none. I've gently flexed it all around and don't see anything.

[attachmentid=951
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[ChrisFoley]

I've gently flexed it all around and don't see anything.

flex it more vigorously
Any crack will be about 3/8" in from the edge

[FlacaProductions]

No cracks. I would think that it’ll tear or click if there was a tear.
I’m going to put to back together.

[FlacaProductions]

Well. It’s back together and it’s holding SOME vac now.
Like 20 seconds worth but that’s better than the NONE of before.
I’m suspecting the rubber seal around the outside?
As I first mentioned, the outer four bolts seemed a little looser than I thought they should be but this is the first time I’ve had one apart.

[Superhawk996]

Grease the paper gasket (very lightly) that is a far more likely leak than the seal. Grease the seal lightly too.

[JamesM]

I think the danger would have been in the expansion of the cell rather than any stress on the diaphragm like part that normally breaks due to use/too much vacuum.

Well, you can pull apart the one with the tangerine mod and see what is up.

(IMG:style_emoticons/default/agree.gif)

but I also doubt its either of those things.

Even if the MPS was exposed to atmospheric conditions at 30,000 ft (which is wasnt) the the vacuum on the diaphragm and cells wouldn't be much different than is sees during engine operating conditions.

If the damage is indeed related to travel I'm going to guess they didn't hold up to being thrown out of a plane on the ground. Even if you packed them well, that is still a lot of inertia. There is a reason VW installed those on rubber isolation mounts.

[IronHillRestorations]

My guess is your suitcase got tossed by baggage handling and the MPSs got a thump that damaged them

[bdstone914]

I once shipped a good MPS and it was dead on arrival. I agree with Perry's idea. I dont see air pressure difference blowing them out.

[FlacaProductions]

Rats.
Both of these were shipped to me and they were fine til now.
In fact, all 3 that I have were shipped without issue so it never occurred to me that they were apparently this delicate.

I am SUPER bummed that these two got messed up - I was right on the leading edge of having some success tuning for cooler head temps at highway speeds.

No time today to mess around - maybe tomorrow. I guess i'm a tiny bit buoyed by the fact that I can get SOME vac out of one unit now. I just wish the issue were more obvious since I don't see any cracks in the diaphragm.

More when I can - thanks for all the input. Again.

[Olympic 914]

Well. It’s back together and it’s holding SOME vac now.
Like 20 seconds worth but that’s better than the NONE of before.
I’m suspecting the rubber seal around the outside?
As I first mentioned, the outer four bolts seemed a little looser than I thought they should be but this is the first time I’ve had one apart.

There is no time, when it is running that the diaphragm is required to hold an absolute vacuum. It is constantly pulling vacuum and changing.

Although many will disagree with this, IMHO a 20 sec leakdown should not or only minimally effect the running.