jimmy101 wrote:Interesting idea.
1. You don't know when it is actually going to fire.
Never stopped anyone from making a traditional burst disk pneumatic.
jimmy101 wrote:2. If the chamber heating is uneven you may (probably will) get the solder holding the round melting unevenly. Really no reason to expect that the entire ring of solder will melt at the same time. I would expect a small portion of the solder to melt allowing the built up pressure to escape dropping the temperature of the remaining gases and the chamber. In other words, I don't think it'll work.
That's my main concern as well, but I'm hoping the copper heat spreader will allow even heating of the solder ring. Although why doesn't the same thing happen in traditional burst disks, that is a small portion of the disk fails and air escapes through it. I think it's because once you have a small puncture it acts as a stress concentrator allowing catastrophic failure of the material. I'm hoping that by the time the solder melts, the structural soundness of the sweat joint will already be compromised enough to fail catastrophically.
Another idea I've been tossing around is having an airtight seal between the cap and chamber and merely holing it in place with a small amount of solder, although I'd need high temp o-rings then.
ShowNoMercy wrote:[1]Why not just forget the burst disk setup adn get a valve made for steam systems? That way you could generate the pressure from steam and trigger it when you want to and [2]not have to worry about failure of joints etc. [3]Also have you thought of superheating it?
[1]I'd eventually like to make a steam piston valve for this, but this design is incredibly simple and will outperform a piston valve too.
[2]Failure of joints is always a consideration in any launcher, the only reason I mentioned that was because I can't use soldering to hold on the fittings, I'm working with temperatures above its melting point. Even if I was using a standard valve, the fittings would still have to be brazed on.
[3]Using superheated steam would be next to pointless if not detrimental. Most of the performance of the launcher comes from the pressure of the steam, not it's heat. I'd much rather have saturated steam at 448 F and 400 psi then superheating my steam to 448 F and still having only 255 psi. Not to mention the negligible performance I'd gain from superheating it also lowers my max allowable working pressure on my chamber because of the degradation of its mechanical properties.
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