Low cost Halloween pop-up character

Step 8 Assemble the pneumatic lift assembly

Glue the PVC into the elbow. Place the assembly up against the V-groove of the Strong Back (wooden dowel) with the elbow down against the plywood. Place the Spacer you made in step 6 between the PVC and the Strong Back's groove near the top of the groove. Glue this into place. Now place the Automotive Clamp over the PVC and the Strong Back. Locate it way between the Elbow and the Spacer then tighten. Slip the PVC over the PVC and check the top and verify the 2 are almost level. If not, trim one or the other until they are. Then glue the PVC Cap on the PVC. If you are the anxious type, the system can now be tested, but be warned the PVC will launch like a rocket (hey maybe that is another Instuctable?).

Comments

[Improviser]

This a very bad idea. You can check with just about any Halloween prop maker with experience (myself included with over 15 years) and they will tell you that using PVC for any pneumatic application is bad. PVC is meant to carry water under pressure, air is a totally different animal that will degrade the PVC and cause it to fail by exploding into shrapnel. PVC also fails quickly if it gets cold. For safety always use cylinders designed/rated for pneumatic applications. My pop-up props use them and they were cheap (like $12 on ebay). It's not worth the chance of causing injury to anyone.

Read the information here if you don't believe me:
http://www.phantasmechanics.com

[Back Roads]

Sorry to all I have been busy working other things and haven't checked this for some time. But a side note I have been using this prop now for 3 years. No problems to report.

So my response to Improviser, the web link you posted to prove your point does not work. I would also ask you and others not to keep spreading internet folk lore without knowing the facts.

So here are some facts. The issue of PVC shattering is common among plastics and is called Glass-transitioning. This is where the molecules freeze and can not take any impact (under pressure or not). To find this temperature of a plastic one should consult a proper source such as the "Modern Plastics Encyclopedia." In there you would look up Brittleness Temperature. For PVC you will find it to be -7 deg F. You will also find PVC is good up to 150-200 deg F continuous use. You can find the same information from suppliers like Port Plastics at http://www.portplastics.com/.

Further investigation of PVC you will find air does not degrade PVC. A common sense test of this would be if it did, home improvement stores could not store the products on the shelf in the open.

To make one nod on, air versus water in PVC pipe. Water does not compress (much) so if it is under pressure in a PVC pipe and there is no air (also compressed) in the pipe, and the pipe is below -7 Deg F, and it is struck with a sharp object, the pipe could shatter. But since water will expand very little, it will carry PVC fragments only a short distance. A PVC pipe with compressed air under the same conditions will Fail in the exact same way. However since air expands it will carry PVC fragments with it a much farther distance as the air expands to equalized with the ambient conditions.

So if you want to use PVC in North Dakota in the middle of winter, outside, you may have a problem, whether it is under pressure or not. For people who live in the south west we don't have a lot of problems with the stuff.

Side note to the Spud Gun crowd, I noticed MythBusters had used a PVC spud gun on their Duct Tap Tater Tosser episode. They claim they are professionals with years of experience.

[Improviser]

Yes,

Unfortunately Doug Ferguson's site phantasmechanics.com has gone offline, the owner retired. He had many years of experience in prop building and is known as the creator of several props for many you see today. The link was to a good article on the hazards of PVC under air pressure and his experiences.

If you are in any business that deals with compressed air (or any gas) you will know that OSHA has severe penalties for use of PVC pipe to carry air. It is just not allowed for good reason.

Maybe this government website will help:

http://www.osha.gov/dts/hib/hib_data/hib19880520.html

A quote from the United States Department of Labor OSHA document:

It is our position that PVC pipe shall not be used as a means of transporting compressed air. This position follows the manufacturer's own statements that PVC is unsuitable for compressed air systems. We do allow the use of certain ABS materials that are specifically designed for compressed air systems. One such product is "Duraplus" air line piping system ABS pipe. However, as in any such system, the manufacturer's specifications on acceptable pressure and temperature considerations must be followed.
******

Another United States Department of Labor OSHA document: Quote:

Last year, a section of PVC pipe being used for compressed air exploded 27 feet above a warehouse floor. A fragment of the pipe flew 60 feet and embedded itself in a roll of paper. Fortunately, nobody was in the area at the time.

A PVC pipe explosion in a new plant in Selah broke an employee's nose and cut his face.

PVC piping buried 3 feet underground at a Yakima manufacturing plant exploded, opening up a crater approximately 4 feet deep by 3 feet across.

Only one type of plastic pipe has been approved for use with compressed air. That pipe, Acrylonitrile-Butadiene-Styrene (ABS), is marked on the pipe as approved for compressed air supply.
******

PVC shatters into pieces
ABS splits lengthwise

You may be lucky is all. I would hate to be the one standing nearby when it fails. Water in PVC only transfers energy, air stores potential energy. So even at relatively low pressures, PVC can suddenly release a tremendous force.
If you rally doubt any of this, you really need to talk to the manufacturer of the PVC pipe you intend to use.

[GTechno13]

I have a PVC pneumatic spud gun which I like to shoot snowballs in the winter. I charge it to 100psi. :) :)

[Back Roads]

Improviser, the portion that pops up is less then 2 pounds. And this design should not be used for anything heavy. The air pressure to activate is only 30 psi, and that pressure is never reached inside the cylinder, because by design it leaks. This allows the prop to return with out a complicated bleed valve. As long as the operator sets this properly, press will never reach to point of exploding. However it may crack over time and at that point it just won't work. If you are designing a pop up to lift a full sized 40 pound prop, then yes design it with the properly rated pneumatics/hydraulics.