john bunsenburner wrote:How come rag? I have figured it because i have not seen many rectangular chambers but i never understood quite why...
It creates uneven forces around the circumference.
Take a balloon, and blow it up. It automatically takes a circular shape, because that's where the forces are balanced. Squash in the sides, it will spring back.
You might argue that's because the balloon's made that way (To which I say, if that's the case, then why don't they make oval balloons as well?), but if you take say a plastic milk jug, which is naturally near rectangular or square and blow into it (or alternately, fill it with water and freeze it), you can see the sides bowing out.
Any vessel with pressure in it naturally tries to expand out to a circular shape.
If that vessel was not originally circular, then this creates stresses on it as the forces try to bend the sides.
With a circular vessel to begin with, the only forces involved are the stretching of the sides under pressure, thus reducing the load the parts are put under.
It depends on the exact shape and dimensions of parts, but I've seen vessels very similar in shape, but with relatively thicker walls than army water canteens fail somewhere under 100 psi.
This vessel had walls about 3-4mm thick and was about 2" across it's widest diameter, and in a parallel hydro test against a PVC bottle for a non-carbonated drink, which had walls about 0.5mm thick, and a diameter of about 3", the PVC bottle won out, in spite of the much flimsier walls and higher diameter.
That gives you an idea of how much the strength of a non circular pressure vessel is compromised.
