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PVC Pressure ratings myth.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: frankrede » Thu Oct 26, 2006 1:12 am

Which ways more a pound of gold or a pound of feathers.
Idiot answer:Gold
Average answer:They way the same
Genius answer: Feathers
A gold pound is less than a regular pound.Get that ton stuff out of here.You had it wrong from the start.
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Unread postAuthor: Boz » Thu Oct 26, 2006 10:36 am

Believe me when I say I know that pressurizing a PVC pipe to 250+ psi is by no means a smart move, and I am not trying to say its safe. I am just argueing the point that a PSI rating is just that.

The arguement here most people are making is that the volume of compressed gas is far higher than a liquid, giving it a much higher potential energy. This is completely true, and also the means that makes these cannons function.

So to be safe I myself will never charge a cylinder over 120psi. But you cannot say that PSI is measure differently for water and air, pressure is pressure.

Guess I'm just playing devils advocate :twisted:
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Unread postAuthor: Brian the brain » Thu Oct 26, 2006 11:01 am

This topic has been chewed up and spat out many times over.

The rating is for static pressure. Meaning the pipe is not meant to move.Moving it around can cause it to warp and bend and build up other stresses that are not concidered within the rating.

These pipes are meant to be used UNDER GROUND!
Covered in sand it is compressed by the weight above it, and it's static.

True, if you were to use it for compressed air, buried underground, there would be no difference compared to the use of water.
However, an- out in the open, warping, and possible bumped pipe can crack.
The difference between escaping water under pressure and gas under pressure, is ,gas releases more explosively, making a cracked gas reservoir much more dangerous.

It's not the medium contained that makes the difference, when it comes to rating, it's the different use!!!
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: POS » Thu Oct 26, 2006 3:09 pm

Dr.Doom wrote:apparently this guy says we don't need to...


When the PSV is rated to lets say 230 psi, you can put 250 on it, without it exploding. There is a window of safty ont that rating. It would be stupid to put 230 on the PVC, when i explodes or bursts at 232 psi, wouldn't it ?

So on a 230 rated PVC pipe, you can safely put 230 psi pressurized air, no danger there.
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Unread postAuthor: nicholai » Thu Oct 26, 2006 3:57 pm

plumpthumb wrote:Duuuuh! It doesn't matter! PSI is PSI. doesn't matter if it is water or golf balls,
it is all the same! One may take a little more or less than the other but if you are monitoring the pressure it makes no difference. The point is to use a guage to keep track. Why argue a useless point? The man is right.


somewhat right...

a pressure rating is a pressure rating no matter how you look at it, correct.

the medium under pressure DOES matter, compressed air has much more energy than hydraulic (liquid) pressure. The pipe bursting from over-compressed air will most likely explode while a pipe overpressurized with water will actually be quite boring. I saw a video of some 3/4 CPVC bursting at like 10,000 psi or something and it was pretty boring.

A good rule of thumb to keep to: Simply don't pressurize over 100-125 psi. That is more than enough pressure you need to do some serious damage or get some distance.
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Unread postAuthor: frankrede » Thu Oct 26, 2006 10:43 pm

Lets all just follow brians example and go metal:D
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Unread postAuthor: joannaardway » Sat Oct 28, 2006 11:42 am

Right. I have to be pedantic and say that the gold does actually weigh (weighs, not masses) more.

Because, in any case, no two objects can exist in the same space.

By having the gold and feathers you are displacing air (yes, like Archimedes' principle with water - if it floats, it displaces it's weight, it if sinks it displaces it's volume. Same applies for air.)

As the feathers displace more volume, then they displace more air, thus resulting in the "boyant" force exerted by them on the air being greater, thus when you "weigh" them, the resultant force will be less, meaning that the weight of the feathers (not their mass) will be less.

A tonne is a unit of mass. Meaning that although the masses are identical, their weights are different due to Archimedes' principle.

Prove it to yourself by taking two different sized objects that weigh the same and then weighing them under water. The larger one will now apparently weigh less.

Don't try and impose pressure limits on people. Some want only 30 psi, some want 300. It's their choice. We can advise them on what is safe for the pipe to take, but not what they want to/should use.
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