pic: T-Shirt Launcher, still needs a chasis

[Daniel_LaFleur]

Originally Posted by Mr. Freeman

Seems to me that if PVC rated at 400+ PSI fails at anything less than 400 PSI then it was either:
A) Not actually rated
B) Not properly used (exposed to conditions it wasn't rated for, etc.)

Apparently you did not read my previous post.

PVC is not rated for compressed gasses. It is only rated for liquids. The difference is not in the pressure itself (as 400 PSI is 400 PSI). The difference is in the failure effect. With liquid the PVC will split and release it's pressure quickly (as liquid is only compressed as far as the gas within the liquid allows) while the gas will rapidly expand and sunder the PVC causing it to expel the shards in all directions.

Whats worse is that PVC gives no (or very little) warning that it is about to fail and that the PVC item in question may have been operating "properly" for years (as was the case with the 1 liter volume I discribed earlier).

Oh, and another thing ... The forces on the barrel and breach are almost instantanious (sp?), whereas the t-shirt takes time to be expelled from the barrel ... thus the entire force of the air is applied to every surface (universal gas laws) within the cannon. So when you fire the cannon it puts almost 60 PSI (assuming thats the pressure you are using) on every portion of that cannon being used until the t-shirt leaves the barrel. Not only that but those forces are applied as a shock load which is about as bad as you can apply to PVC due to its brittleness properties.


as to another question in this thread:
And as far as making PVC safe for use with compressed air ... the only way you can do this is to ensure that the blast from a catastrophic failure (when it happends) is contained.

And lastly ... if someone doesn't want to listen and makes a pneumatic device out of PVC, well I personally don't care too much. If they want to hurt themselves thats fine. But when they state that they are going to use it for 'marketing' then I have to stand up and be heard, because those near the device may not fully understand the dangers that the device presents.