Thread: PVC air cylinders

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Originally Posted by Industen

Gee way to plug my prop

PVC exploding is alot different then framework detaching. It's like comparing a hand grenade to to a water ballon.

Is it different? Well actually it is but not like you are thinking. If you believe PVC is dangerous because it will shatter and hit a TOT with sharp pieces of PVC, then using it as a frame is even more dangerous. Let me explain.



Industen you know how the air cylinder works, any kind not just PVC....they all work basically the same way.

Now we all know PVC changes at temps somewhere around freezing and now it will act like a hard plastic and splinter if it fails. BUT SOMETHING will have to cause that failure not just pressure. The pressure ALONE will not cause it unless you are using a unsafe pressure to begin with.

The myth is PVC becomes WEAKER at lower temps and that causes the failure. It's not. The PVC it self actually gets stronger and the difference is the way it acts after failure. If a failure happens at low temps it now brittle and splits into pieces.

Something has to cause the stress for it to fail in the first place not just the "safe" air pressure. Since ALL air cylinders have basically the same working parts...a cylinder, a piston, some type of O ring/rubber stopper and a cap. The most stress is going to be put on the cap/top of the air cylinder or the where the nipple goes into the cylinder.

If a failure happens at the nipple (PVC) in all likely hood the nipple comes out or you get a air leak and no pressure. Nothing that will push the PVC to failure.

So the best place for stress on a PVC cylinder is the cap. The piston shoots up and hits the cap with enough force to bust it and cause failure. Since every PVC cylinder I ever built or seen used a limit cord and limited the piston from reaching the top/cap. The likely hood of failure at that point is minimal. But I had failures at that point....not the PVC but the limit cord coming undone.
The piston slammed up against the cap...no explosion or pieces of PVC going every where. In all likely hood you would get a failure with the stopper and piston coming apart and I had that to happen more than once.

Now lets get to using PVC as a frame for a SLAMMING air prop. Just because air isn't going into the PVC doesn't stop it from getting to the point of it becoming brittle IF A FAILURE happens.
But something will need to cause enough stress in the PVC to fail before we worry about if it becomes brittle and shatters.

In your case there is nothing moving in the PVC to cause that to happen, BUT...
But the force your real air cylinders are putting out when it extends and retracts is just as equal as the pressure you have going into the cylinder. So the force of the PVC/frame hitting against each other or the wood base, over and over and over again is more likely to cause more stress than air going into a PVC air cylinder and pushing on the wall or piston.

Take a piece of PVC, put it in the freeze for 30 mins and take it out and slam it against a wall. That's about what you have when using PVC as the frame of a slamming air prop. I bet I know what you're thinking....(at least what I'm thinking ). The PVC can't go anywhere because It has a prop in front of it to stop it.

Maybe not! Look at all the stress points for likely failure you made by drilling holes and putting bolts into the PVC.



Now where would the failure likely to happen? My guess would be where most of the weight and stress is at. If that is where it happens you prop drops and now you have air cylinders slamming in and out with pieces of PVC hitting a wall (or something) and breaking into more little pieces. They're not just going to drop to the floor they will be thrown in all directions.

Now take the same PVC and wrap it in duct tape and put it in the freeze for one or two hours...freeze it. Take it and slam it against the wall and see if it shatters into little pieces. It might break but the duct tape will hold it together.

I realize that's not quit the same as 30psi pressing over every sq inch of the PVC but my guess is the duct tape would be strong enough to hold the PVC together.

Now which presents more danger or the likely hood of a failure, air going into a cylinder or PVC slamming together? With a little bit of caution/duct tape you can prevent a PVC air cylinder from flying all over the place if it failed. No grenade going off....unless you call the PVC shattering on the frame and being thrown in all directions as a grenade

Originally Posted by thisain'tmayberry

From the Plastic Pipe and Fittings Association (PPFA) web site http://www.ppfahome.org/index.html


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So if the PVC pipe industry says don't do it, why would anyone want to take the chance? I'm all for investing a little more in an air cylinder that's designed as an air cylinder and avoiding risky gambles.

Don't mean to preach - just my $.02

Again I will repeat...NO ONE said PVC was made to be used to carry air..........OH wait one second I think I posted link to two companies that did just that. MADE PVC AIR CYLINDERS.

But that's beside the point. As a haunter we use things all the time to make other things out of them.

Hey if you feel good about only using things as they were meant to be used....that's up to you.

So, I guess you're not making tombstones out of the pink board? I know you're not because it wasn't made for that use or meant to be carved with all that dust or fumes going into the air.

And I know you don't own any flicker lights made out of a fuse

And I'm 100% sure you would NEVER used a depleted butane torch tank by drilling out the neck to make a air tank and connect this next to your prop. Now that would be very DANGEROUS since it wasn't made for that......But I know you wouldn't do that. Right? Compressor Question

I also know you would never use fishing line to run a flying ghost what if that line broke and wrapped around a ToTs neck and they took off running.

By the way I'm almost 100% sure air cylinders aren't meant to be used to shoot our air props out at ToTs. I bet you will NEVER find any data that says its ok to use the air cylinder like that.

i built pvc pistons for 2008
YouTube- Scary Jack-In-the-Box

it used 4ft pipes i think it was 1 1/2" pvc and it gave me about a 4ft stroke... i threw these together quickly which is why the movement isn't smooth but it served its purpose as i wasn't using that much pressure because the clown prop weight almost nothing

If you were an expectant mother would you scuba dive to 130' even if there was no data to support the fact that you might injure the fetus?

Would you put a pistol to your head and pull the trigger even if you could see the magazine was out of the gun, if there was no data to support the fact that some guns will still fire a round in the chamber with the magazine out?

What I'm saying is the cost/risk/benefit of using a homemade PVC cylinder over a purpose-built device is not there. I think we can agree that there is enough anecdotal evidence out there to warrant a vigorous discussion about the safety of these homemade devices.

Why assume extra risk if it's just as "Cheap and Easy" to use a purpose-built cylinder?

Madmax, if you're good with that then go for it - that's what makes America great: Freedom of choice, both yours and mine.