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I made this scissor mechanism out of 3/4" 480psi PVC pipe. I also made the PVC air cylinder out 1" pipe for the cylinder and 3/4" for the ram. This took about 3 hours to make once I had all the pieces.

Its going to be used in a Clown-In-The-Box. It reaches a height of 5 feet and collapses down to 18 inches.

Video
 

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Looks like it going to work very well. You might want to add a spring at the bottom on the base to push the scissors apart so it will fold back up.
 

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Show you going to show us how you built it?please. (maybe I should just order a semi truck full of PVC)LOL so many neat projects.
 

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Ok, firest the good news, I think you did a fine job making that!

Now for the bad news...NEVER NEVER EVER use PVC for air rams. They can explode very easily and are UNSAFE for you, your prop, and especially the little Trick or Treaters. It's just not worth the pain, injury and law suits that results from shards of plastic imbedding themselves in someones flesh. Please, I beg you, replace that PVC air ram with a commercial Bimba or something RATED for air pressure. I see you manually hooked up a hose rather loosly and that's fine for a demo, but when you hook it up to solenoid valves it WILL take on full pressure and explode. Just a friendly warning, I don't want to see you or your guests hurt.
 

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PVC Ram

Dr. I have used a PVC ram for years. The pipe is rated for 125psi, but I only need 25-30 psi to run my prop. I have never had a problem. Now I am not saying that because the pipe is rated at 125psi you can run it that high. That would be VERY VERY UNSAFE for anyone to be around.

PVC is not designed to take the hammering like a commercial ram so you must build in safe guards and really look at how you are going to use the ram.

Also how much is it going to lift? A pvc stick prop the runs around 10lb's Ok, but try to lift much more than that and you should move to a commercial ram that is built to take that kind of work load and air pressures needed to lift that kind of weight.

Here is one of my PVC props, it will lift up 7 1/2' but it is only lifting a head, a shirt and two gloved hands.

It also has stops to make sure that it does not go to full extension.
 

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FWIW, PVC shouldn't be used for compressed air at all. The pressure rating is for liquid, not compressed air / gasses. That whole thing about fluids don't compress and thusly if there is a rupture, it won't shatter, blow apart and release tons of energy like a compressed gas will.

If you're going to use PVC for air, at the very least, use Schedule 80. It has a significantly thicker wall and IME, doesn't shatter quite like your standard SCH40 white PVC does. (SCH80 is almost always grey / black).
 

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Ok, firest the good news, I think you did a fine job making that!

Now for the bad news...NEVER NEVER EVER use PVC for air rams. They can explode very easily and are UNSAFE for you, your prop, and especially the little Trick or Treaters. It's just not worth the pain, injury and law suits that results from shards of plastic imbedding themselves in someones flesh. Please, I beg you, replace that PVC air ram with a commercial Bimba or something RATED for air pressure. I see you manually hooked up a hose rather loosly and that's fine for a demo, but when you hook it up to solenoid valves it WILL take on full pressure and explode. Just a friendly warning, I don't want to see you or your guests hurt.
I agree 1000% with DR Moribus. You did a great job on the prop, but if you think about it there is a reason Bimba, Parker, Numatics don't make PVC cylinders. They are dangerous, I know from first hand experience. I almost had the little finger on my right hand blown off when some PVC exploded under 25 psi of air. If you check Charlotte Pipe companies web page they even state that you should not use PVC for gas or compressed air, that serious injury or death can result. Just like Dr. Moribus I'm not trying to get down on you or belittle you I just would not want to see anyone get hurt.
 

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FWIW, PVC shouldn't be used for compressed air at all. The pressure rating is for liquid, not compressed air / gasses. That whole thing about fluids don't compress and thusly if there is a rupture, it won't shatter, blow apart and release tons of energy like a compressed gas will.

If you're going to use PVC for air, at the very least, use Schedule 80. It has a significantly thicker wall and IME, doesn't shatter quite like your standard SCH40 white PVC does. (SCH80 is almost always grey / black).
So Brandon K , if I understand you correctly, when the PVC explodes under a liquid pressure it will dissapate most of the enegry through the liquid? I do understand how pressure works although it is a very basic. What I thought , and had been told, was thet the heat and change in pressure would actually flex the pipe more than a liquid would. Mostly when a liquid is put under pressure it stays at a more constant pressure versus a gas when being compressed when you have a high and low due to the way an air compresser works.
 

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The difference between liquids and gasses under pressure is whether they compress or not.
Gasses (air, etc) compress under pressure, and expand when the pressure drops.
Liquids, on the other hand, usually compress very little.

Water under 500psi takes up almost the same space as water at atmospheric pressure - so if the pipe ruptures, the water is not going to suddenly expand and throw shards of plastic around...it's going to leak out and make a puddle...perhaps, worst case, make a small fountain for a short amount of time as the pressure equalizes.

Gasses, on the other hand, compress under pressure...considerably so (I think it's something along the lines of 5:1 for pressures around 125psi...so, 5 cubic feet of air is being squeezed into a 1 cubic foot box)
So, in the case of a rupture in a container holding a pressurized gas, there's going to be a hell of a lot of expansion of that gas - whether it means the container shatters (throwing shrapnel), or the container turns into a rocket as the gas escapes through a small opening...or, hopefully, the container just develops an opening, and the container is secured well enough that the gas just vents through the opening (think safety valve).

In any case, PVC might not be a good choice for a pneumatic cylinder if there are going to be people around who could be hurt if it does fail catastrophically.



That's a kick-ass scissor mechanism, by the way...the speed of it is great - I can just imagine it jumping up as people pass by! Should make quite a few people jump!
 

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Dr. I have used a PVC ram for years. The pipe is rated for 125psi, but I only need 25-30 psi to run my prop. I have never had a problem. Now I am not saying that because the pipe is rated at 125psi you can run it that high. That would be VERY VERY UNSAFE for anyone to be around.

PVC is not designed to take the hammering like a commercial ram so you must build in safe guards and really look at how you are going to use the ram.

Also how much is it going to lift? A pvc stick prop the runs around 10lb's Ok, but try to lift much more than that and you should move to a commercial ram that is built to take that kind of work load and air pressures needed to lift that kind of weight.

Here is one of my PVC props, it will lift up 7 1/2' but it is only lifting a head, a shirt and two gloved hands.

It also has stops to make sure that it does not go to full extension.
Well, good luck with it...and I mean that. If your regulator fails or something else fails to keep the pressure down I wouldn't want to be anywhere near it. It's just russian roulette your playing with yourself and your guests. Just because you have been lucky so far isn't proof PVC rams are safe. It just means you have been lucky. Also, PVC gets brittle over time. Just a thought to keep in mind.
 

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Discussion Starter #19
Its late and I just got off from work. I will have the how to and video tomorrow morning. Sorry for the wait.

As for the air cylinder made from PVC. Here we go on this issue again. I have read a lot of posts regarding this issue here on halloweenforum.com. I fully understand the risks involve and my reasoning is as follows:

1. The scissor prop that I made with the PVC air cylinder only requires 30 psi to activate it.
2. I use the thicker walled, 480 psi for the cylinder part.
3. I do not live in a very cold climate, so shattering the PVC pipe due to cold weather is not an issue.
4. The bimba cylinder that Push Eject linked to is $40 plus shipping where as the PVC pipe jig is $3-4
5. I can make whatever length and throw that I want.

Now I must say that other props I have made all use screen door closers and I have had nothing but great results with them. The problem is that the throw is not long enough for some props. I will be trying out a Bell bicycle pump that I got a WalMart this year for a prop. It gives 15" of throw which is great!
 

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That is a pretty cool design. I have considered building a horizontal scissor prop myself out of metal. Have you tested this under a load at all ? Watching the video I am curious how it would lift upwards with weight on it and if it would try to bend to the side under the weight of your prop ? Also, does the arm of the scissor attached to the ram stay pretty well in line, or do you think some sort of "track" will be needed to keep the rod and arm straight ? :confused:
 
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