SpudFiles

Everything we talk about here is gage pressure, which is relative to surrounding pressure (usually 1 atmosphere) rather than the absolute pressure.

All the numeric values I use for this example are just made up to give you the basic idea of what I am saying.
It is safe to say that a sealed piece of PVC rated for 100 PSI will explode when 200 PSI is pumped into it. Say you were able to surround that piece of PVC with 100 PSI air, it would be equivalent to filling that chamber to 100 PSI under normal conditions, or if the outside conditions were 200 PSI, the chamber material would experience a net pressure of 0 PSI.

Using multiple chambers contained within each other, it could be possible to achieve unrealistically high absolute pressures, I have created a diagram that shows the basic concept using two chambers.

Before anyone goes and tries this, here is a warning. Using many chambers to sequentially step down from the pressure in the main tank may look good when you imagine the inner chamber containing its maximum pressure, but you must also look into what could happen when the inner chamber is empty. We are familiar with pipe explosions here, but we know almost nothing about implosion.
Worst case scenario: your inner chamber collapses causing a massive pressure drop in your second chamber causing it to implode and so on, the combined high pressure gases from imploding chambers could lead to explosion of the outer tank if the combined pressure of the contained gases exceeds the rating of the outermost wall of PVC, possibly by a large amount. This could result in an explosion.
The probably of such a situation is not high (hopefully impossible), just be careful when delving into new concepts especially since there is little information concerning subjecting PVC pipes to negative pressure.

seems like a lot of work when you could just use metal piping rated to higher pressures.

This doesn't unnecessarily have to be done using PVC. This could be used on anything to achieve higher pressures than the material ought to allow. Just playing around with the idea.

this is the same consept as duel bust disk canons so the idea of relitive pressure has been thought of http://www.spudfiles.com/spud_wiki/inde ... burst_disk

Not worth it.

You'll be using a double thickness chamber plus the air cavity which will increase weight and external dimensions.

Single wall rated to what you need is much more reliable.

it would still put a ton of pressure on the pvc, but it would work.

In theory this would work, but the bulk and size of it would be unneccesary and make it more worth while to find a better solution, like higher rated pipe. If you don't mind size and weight, it is possible to incase pipe in reinforced concrete to make it extremely strong. I've never done it for a compressed air chamber, but i have done it for large bore black powder cannons and have had no falures yet (and have fired dozens of rounds from them). But the method is a pain to do right.