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sweet pneumatic video

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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that is sweet
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Total votes : 6
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Unread postAuthor: SpudBlaster15 » Sun May 20, 2007 2:56 pm

clide wrote:Low temperature makes the pipe stronger, but more brittle. And you are still using a limited sample as a basis for your conclusion that ABS is always safe. I am fairly confident I could take a piece of PVC and pressurize it to 1000 psi without it blowing up, does that mean it is safe to do? Nope.


The purpose of the first test was to show that cold temperatures do not make ABS brittle and more prone to failure as they do to PVC.

My tests were well outside the confines of what most pneumatic builders will put their cannons through. I highly doubt anyone would be stupid enough to instantaneously pressurize an ABS chamber to 250 psi and expect it to hold, and even if they did, and the chamber exploded, it would be reasonably safe, because ABS fails cleanly. Do you know what happens when pressure rated PVC is subjected to the oxy/propane test? It turns into a frag grenade.

clide wrote:I think you completely fail to grasp the idea of what makes something safe. Do you think it was just a marketing decision by the piping companies to mark the ABS as DWV? No, it was a decision by highly trained engineers. If it was safe to use for pressure then it would be marked that way. Could you explain to me why they would decide to mark a pipe as DWV when it would be safe to use for pressure applications? Because I can't think of a reason.


Do you think it was a marketing decision by the piping companies to clearly warn consumers that NSF-pw PVC pipe is not to be used with compressed gases because of it's failure characteristics? No, it was a decision by highly trained engineers. If it was safe to use with compressed gases, it would be marked that way. Could you explain to me why they would decide to mark a pipe as 'unsafe for compressed gas use' if it was safe for such applications?

Because I can't think of a reason.

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Unread postAuthor: SpudBlaster15 » Sun May 20, 2007 3:14 pm

This gun definitely shoots faster than 350fps...

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Unread postAuthor: Velocity » Sun May 20, 2007 3:29 pm

Spudblaster15: There is a difference for why they are not pressure rated. Both ABS and PVC pipe are not rated for compressed air. However, ABS is not rated for compressed air because it will fail at relatively low pressures. PVC pipe is not rated for compressed air because even though it can withstand the pressure of compressed air, if it does accidentally fail, due to shock or similar situation, then it will explode into many fragments.

That being said... even though you have shown that ABS can hold some pressure, it still is not meant to hold pressure. PVC pipe is meant to hold pressure. With proper usage and pressures, a PVC pneumatic will not fail. However, with proper usage and pressures, an ABS pneumatic still could fail. Sorry if that sounded a bit unclear...

By the way, I think some of your GGDT numbers might be a little optimistic... the piston probably weighs closer to half a pound (8 ounces). My GGDT has a Cv unit next to the flow coefficient number, not a % sign like yours does... anyway, for mine, I plugged in about 23 for the Cv. I'm not really sure though; clide is good at GGDT, he could probably explain it much much much better than I could.
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Unread postAuthor: clide » Sun May 20, 2007 3:44 pm

SpudBlaster15 wrote:The purpose of the first test was to show that cold temperatures do not make ABS brittle and more prone to failure as they do to PVC.

My tests were well outside the confines of what most pneumatic builders will put their cannons through. I highly doubt anyone would be stupid enough to instantaneously pressurize an ABS chamber to 250 psi and expect it to hold, and even if they did, and the chamber exploded, it would be reasonably safe, because ABS fails cleanly. Do you know what happens when pressure rated PVC is subjected to the oxy/propane test? It turns into a frag grenade.

You are still applying the mentality that all ABS is made equally. What I am trying to say is that the company has no reason to keep up that standards throughout every batch.

Can DWV ABS be safe to use? Absolutely, if you pressure test every gun you build with it, but beyond that I would hardly call it safe.
SpudBlaster15 wrote:Do you think it was a marketing decision by the piping companies to clearly warn consumers that NSF-pw PVC pipe is not to be used with compressed gases because of it's failure characteristics? No, it was a decision by highly trained engineers. If it was safe to use with compressed gases, it would be marked that way. Could you explain to me why they would decide to mark a pipe as 'unsafe for compressed gas use' if it was safe for such applications?

Because I can't think of a reason.


I never said it was safe. I'll be the first to tell you that putting compressed gas in PVC pipe is very dangerous. But I would rather put it into something that I know was designed for pressure and held up to a quality standard in production than something that wasn't.

Heck I would even say that the safest plastic launcher you could make would be a solid walled ABS gun that has been pressure tested well above the working pressure, but I know that people won't pressure test well if at all (the "this guy's gun didn't blow up" or "my last gun didn't blow up" mentality is too common), so my general recommendation for what others use is pressure rated PVC pipe because it is held to standards.
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Unread postAuthor: Hotwired » Sun May 20, 2007 3:51 pm

rmich732 wrote:Spudblaster15: There is a difference for why they are not pressure rated. Both ABS and PVC pipe are not rated for compressed air. However, ABS is not rated for compressed air because it will fail at relatively low pressures. PVC pipe is not rated for compressed air because even though it can withstand the pressure of compressed air, if it does accidentally fail, due to shock or similar situation, then it will explode into many fragments.


Wrong, I've said this before and I'll say it again.

Pressure rated ABS pipe IS rated for use with compressed air.
NO type of PVC pipe pressure rated or not is rated for compressed air.
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Unread postAuthor: SpudBlaster15 » Sun May 20, 2007 3:54 pm

rmich732 wrote:even though you have shown that ABS can hold some pressure, it still is not meant to hold pressure..


Ahem...

http://www.ppfahome.org/pressure.html

"ABS, PE and PVC materials are all available with 73 F stress rating for use in pressure piping."

rmich732 wrote:Both ABS and PVC pipe are not rated for compressed air.


http://news.thomasnet.com/IMT/archives/ ... ?t=archive

"Because of needs specific to the dynamics of these systems, trusted plastics such as PVC and CPVC are out of the running. The use of these materials in a compressed air system means that, in the case of a failure, air within the pipe could suddenly decompress and send shards of the shattered plastic flying in all directions."

"Specially engineered and modified thermoplastic, known as ABS, proves to be the best solution. This material is ideally suited to compressed air systems due to its strength, durability and, most importantly, due to its trait of responding to severe impacts with little more than a crack or a split. The fissure that opens in the material serves the purpose of releasing the air pressure with considerably less danger than would be present in the event of a bursting PVC shaft."

Looks like you are incorrect on all accounts, except for your statement involving PVC not being rated for gas pressure...
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Unread postAuthor: clide » Sun May 20, 2007 4:01 pm

Here is my GGDT of the gun, being optimistic on some variables. It is very sensitive to vent diameter and pilot volume due to the nature of the valve. I guess you are using golf balls with the shell removed? I don't know what those weigh, so I just used 40 like Spudblaster.
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Unread postAuthor: super spuder » Sun May 20, 2007 4:03 pm

i have not posted here for a bit , so here goes, Rmich, if you don't want to build a cannon out of ABS, you don't have to, no one is making you. It can hold pressure just fine, and if it does fail, i will have a crack in my chamber, oh well, replace it. I don't know if any one mentioned it, but if you drop pressurized PVC it has a high possibility of blowing up and sending hunks of plastic into you, drop pressurized ABS, nothing happens.
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Unread postAuthor: super spuder » Sun May 20, 2007 4:17 pm

vent diameter is .25 inches, and pilot volume is 15 ci
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Unread postAuthor: clide » Sun May 20, 2007 4:38 pm

Male quick connects have an ID of ~.20" and I would be willing to bet that the blowgun is more restrictive than that, but giving you the benefit of the doubt and using a pilot volume of 15 ci and .2" vent diameter, it is bumped up to 380 fps.
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Unread postAuthor: Velocity » Sun May 20, 2007 4:40 pm

Hotwired wrote:
rmich732 wrote:Spudblaster15: There is a difference for why they are not pressure rated. Both ABS and PVC pipe are not rated for compressed air. However, ABS is not rated for compressed air because it will fail at relatively low pressures. PVC pipe is not rated for compressed air because even though it can withstand the pressure of compressed air, if it does accidentally fail, due to shock or similar situation, then it will explode into many fragments.


Wrong, I've said this before and I'll say it again.

Pressure rated ABS pipe IS rated for use with compressed air.
NO type of PVC pipe pressure rated or not is rated for compressed air.


We aren't talking about pressure rated ABS pipe; we are talking about ABS DWV pipe, which is NOT pressure rated. If this whole time the arguement was whether pressure rated ABS is suitable for pneumatic construction or not, then I change my view. Pressure Rated ABS is one of the best pneumatic materials. For me, in terms of common plastics, it ranks like this for pneumatics:

ABS pressure rated
PVC pressure rated
PVC DWV
ABS DWV
ABS Cellcore
PVC Cellcore

ABS pressure rated pipe is very scarce where I live, and expensive too.

EDIT: I think we need to define this argument a bit more... those who are advocating ABS pipe, what type of ABS pipe? Pressure rated, DWV, or cellcore? I know that I am arguing for pressure rated PVC
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Unread postAuthor: super spuder » Sun May 20, 2007 4:53 pm

what is the seat diameter? and it is a moded blow valve
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Unread postAuthor: Velocity » Sun May 20, 2007 5:02 pm

super spuder wrote:i have not posted here for a bit , so here goes, Rmich, if you don't want to build a cannon out of ABS, you don't have to, no one is making you. It can hold pressure just fine, and if it does fail, i will have a crack in my chamber, oh well, replace it. I don't know if any one mentioned it, but if you drop pressurized PVC it has a high possibility of blowing up and sending hunks of plastic into you, drop pressurized ABS, nothing happens.


I'm not trying to deliberately insult your gun. I like the design, and think it is pretty innovative. Sure, it may be true that if your gun fails, no one will get hurt. But if you made it out of PVC pipe, it would NOT fail, and you would not need to constantly worry about replacing parts. I bet if you compared the number of ABS pneumatics which have failed compared to the number of PVC pneumatics which have failed, you would have a higher percent of ABS pneumatics failing. The failure may mean you just need to buy new parts, but is it worth it spending money on a project that was in a way "expected" to fail? The pressure which most responsible pneumatic spudgunners use in their pneumatics is WELL WITHIN the pressure rating of the pipe (considering that they used NSF-pw fittings and pressure rated PVC pipe).

I am just trying to help out; I don't want to antagonize anyone. Out of the twenty four pneumatics which I have built, sixteen of which have used a piston valve, I have had ONE fail. That particular pneumatic failed (it was the valve) because I overtightened a bushing and had no bumper between the piston and the metal bushing. This was completely my fault, not the materials of the spudgun, and if I had just not overtightened the bushing and had I added a bumper between the bushing and the piston, it would not have failed. I am fairly confident that if that had been an ABS pneumatic, it probably would have failed too. Besides, that failure was not at all explosive; all that happened was a clean crack was created on the piston tee.
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Unread postAuthor: iknowmy3tables » Sun May 20, 2007 5:07 pm

that gun :shock: duct tape, hockey pucks, blowgun actuation on an oversized piston, 2step filling, DWV, ABS, and WTF that is creepy.
that can only dent rotting plywood

AAAAAHHHH how why eeww its just so lacking in quality, so many things could have been done better
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Unread postAuthor: super spuder » Sun May 20, 2007 5:10 pm

well i am just trying to get people off my back :lol: i have got told by soo manny people that ABS is bad for pneumatics, but i myselfe have not hade an ABS failure, so till then, i will probly just keep on using it. It i all plastic, and it is all not that safe, if you want to feel safe use metal.
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