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Unread 29-08-2015, 13:15
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Daniel_LaFleur Daniel_LaFleur is offline
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Re: spud gun/T-shirt gun valve

Quote:
Originally Posted by fovea1959 View Post
Why is running air at 70PSI more dangerous than running water at 70PSI?
This is a commonly asked question. and the reason is 2 fold:

1st is the compressibility of air vs the incompressibility of water. This means that when a vessel holding pressure water ruptures, all of the pressure is relieved with only a small fraction of expansion ( IE pushing of the shards). When a vessel holding air ruptures, the pressure is released over time carrying debris with it.

2nd is the failure mode of most plastics. When brittle objects rupture (such as PVC) the failure mode is to create shards that are sharp. Since air does not relieve all the pressure at once, it carries these shards with it as it expands to fill the 'new' area (relieves the pressure). This creates high velocity sharp projectiles .

Believe me when I say there is VERY GOOD REASON that most plastic volumes carry the warning that they are only pressure rated for liquids (take it from someone who has seen this up close ... and is lucky enough to still be here).
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