28 replies to this topic

[keef]

Yeah, I'm a wuss. I'm scared to use my homemade air gun because I read on a airsoft forum that PVC+ pneumatic power= bad. PVC is meant to hold water, and air has more pressure that water. So, the PVC's PSI max is 200 (example) and air has twice the pressure, so should I only go up to 60 PSI?

Also, could I use PVC and a solenoid to make a Super Soaker?

[Kid Flash]

When i pm'ed slug he said the max pressure for pvc is 100 psi. I on the other hand will probably go from 60-80 when I get mine finished...

[keef]

Well, I understand that, but PVC is meant for water's 100 PSI, not air pressure.

[Shadow 92]

CLICK ME!

Read Carbon's post, its at the top of the page. We had a pretty informative discussion on gas laws and pressure.

[Kid Flash]

Well, I understand that, but PVC is meant for water's 100 PSI, not air pressure.

pvc is made for over 100 psi for water... what labels are you reading?

[keef]

I'm using it for air. And normal air has 9/10 more pressure than water. Gas's atoms are always moving, and liquids are lazy, they just go with the flow. When there is more pressure with the wild energy, the gas is constantly moving, and any sudden bump can make it explode.

[veginator]

You are such a panzy. Do you know how hard it is to break sch. 40 pvc? The only way you could break a pressurized vessel would be to swing it as hard as you could against a tree or something like it. It wont do anything if you just drop it on the ground or bump it.

Edited by veginator, 02 April 2008 - 07:50 PM.

[keef]

Tough guy. Wow, oh wow, oh wow.

I'd prefer not to have plastic in my fucking body, prick.

[veginator]

What kind of pressures do you plan on using in this gun anyway. 40? 50?

[el swifto]

What kind of pressures do you plan on using in this gun anyway. 40? 50?

He hasn't decided yet, as it says in the first post.


If it is "pounds per square inch", then PSI with air should be the same as with water.*


*Disclamer: I don't this for a fact, but it makes sense.

[Doom]

I've pressurized pressure rated PVC beyond 120 PSI before and I've lived to tell about it. With that being said, I don't see any point in most applications for pressures higher than 60 PSI except in regulated systems where one tank has higher pressure than the other. Use a safety factor of at least 3 on top of the already conservative pressure rating and you won't have a problem. In Nerf, you don't have to use larger pipes typically, so the pressure ratings are already beyond what most air compressors can do due to the reduced internal surface area per length.

First off, read the post referenced above by Carbon.

The pressure is the same for both water and air. Pressure refers to how much force per unit area is applied. Pressure is just a measured quantity. 50 PSI air pressure is the same pressure as 50 PSI water pressure. The problem is that gases expand much more than liquids, so when PVC fails under gas pressure it explodes. When PVC fails under liquid pressure, it cracks and leaks, maybe somewhat violently, but it doesn't explode.

I've seen a video of a PVC tanks exploding from being compressed too much air, but the gun took a hatchet to the tank at first so it wasn't even realistic.

Use reasonable pressure, don't damage the pipe, and use general common sense and you have nothing to worry about.

[imaseoulman]

Misconception: Air has more pressure than water.
Fact: 100 PSI is 100 PSI. It doesn't matter if it's liquid or gas.
The major difference between 100 PSI of air and 100 psi of water is the potential energy (I'm using that term loosely so don't flame me). When water is compressed to 100 PSI, there isn't very much change in its volume. That means when the pressure is released, it's not expanding much. If it's not expanding much, it can't propel anything very far. Air, however, when compressed to 100 PSI has had a dramatic decrease in volume. When the pressure is released it's going to rapidly increase in volume and can therefore propel things very far and fast. So if PVC was overpressurized with water, the resulting bursting of the pipe wouldn't be much more than spewing water. The PVC wouldn't be propelled very far (likely not at all, just crack). If PVC is overpressurized with air, the resulting pipe burst could send PVC shrapnel very far and fast.

However, 60 PSI (probably the max you'll need for any gun), isn't enough to do anything. If it were very cold and you took a hammer to it, yeah you might have problems, but nothing lethal. There is virtually no danger with using 60 PSI with PVC.

[Quilan Fett]

First of all, let me say: I'm scared too.

I'm using it for air. And normal air has 9/10 more pressure than water. Gas's atoms are always moving, and liquids are lazy, they just go with the flow. When there is more pressure with the wild energy, the gas is constantly moving, and any sudden bump can make it explode.

Which weighs more, a pound of bricks or a pound of feathers?

Which was more pressure, one pound per square inch of air or one pound per square inch of water?


And veginator, From http://internettrash...epage/spud.html

--Compressed air is not safe like compressed water!!!--

-- Why? Water doesn't compress much, but at 100PSI, air is compressed into about 1/7th its original volume, which means that if the pipe cracks, your gun has become a bomb. There'll be shrapnel which can literally blow your arm off (hey, I said it was manly). PSI means pounds per square inch.. picture 100lb weights pressing outwards on every single square inch of your gun's air chamber. Respect it! Here's a sobering excerpt from some email I recieved:

"As a PVC fittings manufacturer your contraption scares the hell out me... It is right up there with some of the most dangerous things anyone could do. If you had ever seen the damage that could occur to your body if it ever did explode you would never build it out of PVC...

I have personally come into contact with people who have not heeded the warning, it is not a cool sight."

Edited by Qui'lan Fett, 02 April 2008 - 08:22 PM.

[CaptainSlug]

Here's the bottom line.

The reason to never go above 100ps with SCH40 or SCH80 products (which are rated for 300-600psi of water pressure) is because 100psi of gas will not be stressing the pipe significantly. So external shock is not likely to result in an explosion unless you specifically are intending to puncture it somehow. In which case you probably deserve to die.

Any gas pressure level is going to be equivalent to water pressure levels. But gas pressure is always more dangerous. While the amount of stored energy is the same, pneumatic pressure can release it at a much higher rate (more violently) than hydraulic pressure can.

Edited by CaptainSlug, 02 April 2008 - 08:43 PM.

[Quilan Fett]

Here's the bottom line.

The reason to never go above 100ps with SCH40 or SCH80 products (which are rated for 300-600psi of water pressure) is because 100psi of gas will not be stressing the pipe significantly. So external shock is not likely to result in an explosion unless you specifically are intending to puncture it somehow. In which case you probably deserve to die.

How is that a reason not to?

[bpso86]

Misconception: Air has more pressure than water.
Fact: 100 PSI is 100 PSI. It doesn't matter if it's liquid or gas.
The major difference between 100 PSI of air and 100 psi of water is the potential energy (I'm using that term loosely so don't flame me). When water is compressed to 100 PSI, there isn't very much change in its volume. That means when the pressure is released, it's not expanding much. If it's not expanding much, it can't propel anything very far. Air, however, when compressed to 100 PSI has had a dramatic decrease in volume. When the pressure is released it's going to rapidly increase in volume and can therefore propel things very far and fast. So if PVC was overpressurized with water, the resulting bursting of the pipe wouldn't be much more than spewing water. The PVC wouldn't be propelled very far (likely not at all, just crack). If PVC is overpressurized with air, the resulting pipe burst could send PVC shrapnel very far and fast.

However, 60 PSI (probably the max you'll need for any gun), isn't enough to do anything. If it were very cold and you took a hammer to it, yeah you might have problems, but nothing lethal. There is virtually no danger with using 60 PSI with PVC.

Here's the bottom line.

The reason to never go above 100ps with SCH40 or SCH80 products (which are rated for 300-600psi of water pressure) is because 100psi of gas will not be stressing the pipe significantly. So external shock is not likely to result in an explosion unless you specifically are intending to puncture it somehow. In which case you probably deserve to die.

Any gas pressure level is going to be equivalent to water pressure levels. But gas pressure is always more dangerous. While the amount of stored energy is the same, pneumatic pressure can release it at a much higher rate (more violently) than hydraulic pressure can.

You guys hit the nail on the head. The pressure will be the same, but the key word here is COMPRESSIBILITY. You should be fine though, and if you're worried wrap it in duct tape/gorilla tape/more tubing.

[keef]

Ok. Thanks! I probably would stay around 40 PSI anyways. 60 at the most.

[puggy]

Is it sch. 40? I take a 1/2" sch 40 tank up to 130 psi no problem all the time.

If it helps i also use a ball valve, you guys don't know much about pvc. Look at spudfiles.com for some help

[BendyStraw]

Is it sch. 40? I take a 1/2" sch 40 tank up to 130 psi no problem all the time.

If it helps i also use a ball valve, you guys don't know much about pvc. Look at spudfiles.com for some help

The issue isn't whether or not PVC or CPVC can handle high pressure. I've read stories of people taking their spudguns and nerf guns up above 100 PSI all the time.

The issue here is that PVC, when under high air pressure, fails very poorly. Even though you built something that can handle the pressure, that doesn't take away the fact that you are essentially running around with a bomb in your hands.
So therefore, if you do something wrong like forgetting like glue your gun together:
http://www.spudfiles...ded-t13852.html
You stand a very real risk of hurting yourself or someone else. That was just after one search, and I know for a fact that external stress like dropping or bumping a tank might also cause it to fail. I know that forgetting to glue properly is an obvious mistake, but do you really want to maximize the damage to yourself and others should a mistake happen?

Granted, the explosion that results from a bad failure will be much smaller with low PSI, but bringing the PSI up will only increase the risk, should a failure occur.

[Carbon]

Also, the rated pressure on 1/2" PVC is much higher...660 PSI. So, the 130 PSI you're taking it to is well within the safety factor of three that Doom mentioned.

Most discussion of air tanks aren't talking about skinny PVC. Larger diameters have lower pressure ratings, and thus, lower safe pressures.

[keef]

I'm using 1" PVC if that makes a difference. I want to go up to 2" though.

[Kid Flash]

I'm using 1" PVC if that makes a difference. I want to go up to 2" though.

Speaking of 2 inch pvc... Does anyone know the pressure ratings for it? I got a few feet from some construction workers that didn't need it a while back so I've been using it...

[jwasko]

I've taken 2" to almost 100psi without any problem, as long as it is Schedule 40 PVC.

I think it's generally accepted that 100 psi is the absolute upper limit of what you should use for just about any size of sch.40 PVC, really...and if you keep it under 70 it should be no problem at all unless there is some flaw/damage already don to the PVC.

[Doom]

If the pressure rating isn't printed on the pipe, it's not schedule 40 or 80. You could have a piece so small that the pressure rating isn't on there too.

Next time you have a question like "What's the pressure rating of 2 inch PVC pipe?" try some Google searches. It saves everyone time when you use Google. I'll save you time now and just give you a good link: http://www.harvel.co...ch40-80-dim.asp