Carbine preservation

[ChipS]

I don't think it works quite this way

With all due respect, it pretty much works exactly this way. It is more complicated than as discussed here but the mechanics presented I believe are factual.

As you noted, at rest the air pressure in your chest is the same as the air pressure outside your chest. The only work the diaphragm and chest muscles have to do during breathing is to overcome friction loss in the airways and maybe the stretching of the lung tissue, which in normal healthy lungs is minor. That's why they developed the SCUBA regulator, to equalize the pressure in the lungs to the higher water pressure at depth so the diver can inhale and exhale.

However, regarding the pressure inside the sealed and evacuated bag, it is something less than the 14.7 psi (+/-) atmospheric presssure outside the bag. That's why they call it a vacuum. Using a common vacuum cleaner as a vacuum pump, the pressure in the bag will not be true (not gauge) zero, a perfect vacuum, but it will be something less than the '14 psi' outside of the bag. The forces resulting from the pressure differential that are not resisted by the solid material in the bag will be resisted by the diaphragm tensile strength of the bag material - which for modern plastics can be quite high. It's the same principle as the pressure hull of a submarine except the hull (a vessel) is in compression and the vacuum bag (a diaphragm) is in tension to balance the (lower) internal and (higher) external forces.

If you reduced the internal pressure enough the bag would rupture as you noted, but the vacuum cleaner cannot provide that much vacuum (except as noted below). If you reduce the internal pressure at all the bag will collapse in every dimension to reduce the internal volume, trying to re-equalize the pressures. When the bag collapses on a sharp point (like the corner of a magazine) a very high point load is exerted on the bag at the point of contact, exceeds the strength of the bag material and perforates the bag. It does not take much vacuum to make this happen on a very sharp point in the bag (think about an ice pick).

Like I said, the detail mechanics of this issue are more complicated than we have discussed and nobody here really wants to hear about them, but I think the general principles (and common experience examples) I have noted are pretty much true. There is an infinite number of shapes and materials that could be placed in a vaccuum bag and we can't generalize on whether they all will or will not be damaged. I don't think an assembled firearm would normally be damaged in a domestic service vacuum bag. My only point was that if there are any thin, weak unsupported sections or projections of a wood stock (like the thin highwood area on a carbine), or of anything else placed in the bag, they could deform or break if not supported prior to evacuation. Done, Peace, Out. ChipS

[Bill Hollinger]

I think the most one could hope for when pulling a vacuum on a bag with a solid non-flexing content may be as high as 10 to 15 in hg? Not enough to damage the bad with the slide or other edges on a carbine.

FYI, there are two sides to a SCUBA regulator; a high side and a low side. The high side is tank psi and the low side is 140 psi max. The second stage regulator from which you breathe uses that 140 psi with an orifice and a lever controlled by a silicone diaphragm so when you inhale the diaphragm is drawn inward to actuate the lever which opens a valve and allows air to flow to your mouth.

[JimF4M1s (Deceased)]

I feel like I'm back in my physics classroom. Good explanation.