Monday, May 14, 2012

Overpressure Valve



Another small life-saving component. This pressure relief valve will be screwed into the suit, such that if suit pressure exceeds 4psi, it opens, bleeding out gas. It would then close again when the pressure was down to 4psi, which exceeds by .5psi what I need to survive. This pressure relief valve, then, would prevent the suit from exploding should the pressurization gas supply valve fail in the 'OPEN' (pressurizing) position, which would continue to pump gas into the suit until the suit bursts. Can't have that! I also have a manual, backup pressure relief valve that I could open should this unit fail (though I need to devise an 'overpressure alarm').

On the first spacewalk, cosmonaut Alexei Leonov was unable to get back into his spacecraft -- why? Because his pressure suit was inflated a bit high, preventing him from squeezing back through the hatch! His overpressure valve (as seen above) had failed, and he had to use his manual backup to bleed out enough gas that the suit went limp enough to crawl back inside! This was a MASSIVE gamble with decompression sickness, but was all he could do -- and it worked. Now --w what if my suit is overpressurized, my own relief valve fails (moisture in the suit pressurization gas could freeze up the valve!), and I'm in an uncontrolled descent (say, the balloon has burnt up, or exploded), and I can't--because of the excessive size of my suit due to over-inflation--can't get out of my seat? Just a few mm can do it, as the pressure suit is quite rigid when pressurized! Well, then I will turn to my backup, manual 'pressure dump' valve, deflate the suit enough to get out of the seat, and bail out. I'd rather take my chances with that decompression ('the bends') scenario than hit the ground in an uncontrolled descent! And where do I put that manual, backup 'dump valve'? Somewhere unambiguous, in easy reach with the suit over-pressurized. And it needs a large, easily-grasped handle as well, so there is no fooling around, I reach for it, turn it, dump pressure, and bail out. But that big handle mustn't interfere with parachute harness straps etc. All stuff that keeps me awake nights :)

Unit screws into a fitting in the suit. But there is a tiny--pinprick-sized--orifice at the bottom of the relief valve, and that's what I'm counting on to remain completely unobstructed for this overpressure valve to work. But what if that pinprick is somehow obstructed, 'failing' this component? I can install a small wire mesh below, to prevent such a thing...a further new complication!

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