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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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PVC Pressure ratings myth.

Unread postAuthor: Boz » Wed Oct 25, 2006 1:36 pm

Hey all I just wanted to add this topic because browsing through I have seen some discussion on the pressure ratings of PVC when used for air.

Some arguements have been made that the pressure rating on pvc is in reference to water pressure, and that it will hold far less air pressure.

I want to make the point that this is NOT true. PSI means pounds per square inch. If your PVC is rated for 280 PSI that means that the pipe can withstand an internal exterted pressure of 280 pounds per square inch, whether this pressure is exerted by water, or air, it is still 280PSI.

Now I will say it takes much less water to exert the pressure due to its density compared to air. But the rating is accross the board.

Think about this. What weighs more, a pound of feathers or a pound of bricks?

If you have a table that can hold a ton of bricks, could it hold a ton of feathers?

a ton is a ton



Just to add, because the pipe is 280 psi doesnt mean every other component you have used can safely operate at that pressure. Check your valve ratings and fittings. There are more peices than just pipe on the cannon. But as far as a rating on pipe is concerned its true to its print.


Thanks all, just my 2 cents :)

- Boz
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Last edited by Boz on Wed Oct 25, 2006 4:56 pm, edited 1 time in total.

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Unread postAuthor: POS » Wed Oct 25, 2006 2:11 pm

No problem. Nice post, for just your fourth post.

Anyway, I want to add, that if you dont know the pressure rate, or you want to test is, first fill the parts that needs to be tested with water, then pressurise it. Why ? If the part explodes, due to a pressure that is to high, and it is only filled with air, the PVC will shatter and fly around like a shrapnel of a grenade or bomb. If you fill it with water first it will just burst, no flying pieces, so lots and lots safer.

Just in case you want to try out ...
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Re: PVC Pressure ratings myth.

Unread postAuthor: Dr.Doom » Wed Oct 25, 2006 3:04 pm

Boz wrote:Hey all I just wanted to add this topic because browsing through I have seen some discussion on the pressure ratings of PVC when used for air.

Some arguements have been made that the pressure rating on pvc is in reference to water pressure, and that it will hold far less air pressure.

I want to make the point that this is NOT true. PSI means pounds per square inch. If your PVC is rated for 280 PSI that means that the pipe can withstand an internal exterted pressure of 280 pounds per square inch, whether this pressure is exerted by water, or air, it is still 280PSI.

Now I will say it takes much less water to exert the pressure due to its density compared to air. But the rating is accross the board.

Think about this. What weighs more, a pound of feathers or a pound of bricks?

If you have a table that can hold a ton of bricks, could it hold a ton of feathers?

a ton is a ton



Just to add, because the pipe is 280 psi doesnt mean every other component you have used can safely operate at that pressure. Check your valve ratings and fittings. There are more peices than just pipe on the cannon. But as far as a rating on pipe in concerned its true to its print.


Thanks all, just my 2 cents :)

- Boz


you have a point but also... pvc was never entended for air pressure, plus it's probably not a bad idea for people on this board to encourage playing it safe pushing it to the limits is dangerous, if a pipe explodes, your gonna get hurt.
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Unread postAuthor: judgment_arms » Wed Oct 25, 2006 3:20 pm

Yes, but if your stupid enough to not allow a window of safety, then please stop using spud guns.
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Unread postAuthor: Dr.Doom » Wed Oct 25, 2006 4:52 pm

apparently this guy says we don't need to...
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Unread postAuthor: pyromanic13 » Wed Oct 25, 2006 5:07 pm

heres a riddle what weighs more a ton of gold or feathers?

your gonna hate the answer...
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Unread postAuthor: Extrusion » Wed Oct 25, 2006 5:17 pm

pyromanic13 wrote:heres a riddle what weighs more a ton of gold or feathers?

your gonna hate the answer...


You mean a ton of gold of a ton of feathers? if so then they both weigh a ton :lol:
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Unread postAuthor: plumpthumb » Wed Oct 25, 2006 6:02 pm

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.
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Unread postAuthor: squeaks » Wed Oct 25, 2006 6:19 pm

He makes a good point, but water pressure is different than air pressure. since water can't be compressed water pressure is caused by the weight of the water above whereas air pressure is caused by air being compressed. I'm not sure how this would effect the pipe differently, but I sure as heck don't want to be the one sitting by the pipe when it's being pressurised to 250 psi.
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Unread postAuthor: pyromanic13 » Wed Oct 25, 2006 7:51 pm

Extrusion wrote:
pyromanic13 wrote:heres a riddle what weighs more a ton of gold or feathers?

your gonna hate the answer...


You mean a ton of gold of a ton of feathers? if so then they both weigh a ton :lol:


nope gold is measured in tonne's ... I think thats how it's spelled.
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Unread postAuthor: Hotwired » Wed Oct 25, 2006 7:58 pm

Well if you've just weighed out a TON of feathers and a TON of gold then it doesn't matter what gold is meant to be weighed in, its still the same :P
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Unread postAuthor: THEMOST » Wed Oct 25, 2006 8:47 pm

I say the FEATHERS weigh more!!! :mrgreen:[/i]
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Unread postAuthor: MisterSteve124 » Wed Oct 25, 2006 9:08 pm

Pyromanic a tonne is a metric ton gold isnt always measuring in tonnes it just can be
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Unread postAuthor: mark.f » Wed Oct 25, 2006 10:01 pm

He makes a good point, but water pressure is different than air pressure. since water can't be compressed water pressure is caused by the weight of the water above whereas air pressure is caused by air being compressed. I'm not sure how this would effect the pipe differently, but I sure as heck don't want to be the one sitting by the pipe when it's being pressurised to 250 psi


Hell, water can be compressed... a little...

Quoting indirectly, (from memory), from my Chemistry book:

"...Liquids can be compressed to a very small percent, but not nearly as much as gases. Mostly, you could exert extreme force on the liquid and only reduce the volume by a very slight percentage..."

Let's look at it these few ways:

Air can behave differently than water under compression and pressure. It expands a lot because it's a gas, whereas water just cracks the pipe and leaks everywhere.

Pipe is MEANT to stay in one freaking place under a sustained pressure. Even if you WERE within the rating of the pipe, (say, at 200 PSI), and you bumped the chamber into an I-beam or dropped it on your driveway, you would be dead.

So, it is perfectly safe and common practice to increase the safety margin when dealing with compressed gas in plastic piping. Get used to it.
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Unread postAuthor: Slugfoot » Wed Oct 25, 2006 10:55 pm

I remember seeing a short video of a large PVC cylinder (deliberately damaged) rupturing under pressure (about 150psi I think). It sent shards of pvc flying in all directions, blew holes through thick cardboard nearby and shredded a shirt that had been hung next to it. The shockwave from the explosion also made the tripod-mounted video camera rock. If I can find the video again I'll put it up. It's a very stark warning of how dangerous this crap can be.
I won't be using PVC to build a spudgun any time soon. I'll stick to copper and steel thank you very much!

Slugfoot.
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