Replies

1. 
   saschafer | May 27, 2008 06:25pm | #1

   CPVC is more shatter-resistant than PVC, but I'd still be leery of using it in a compressed gas situation. I don't know if there are codes that address its use in that application.

   -Steve

    

2. 
   saschafer | May 27, 2008 06:45pm | #2

   One thing that may not be obvious (and that I should have mentioned in my previous reply) is that pressurized liquids and pressurized gases are two completely different animals. Most liquids are all but incompressible, so it doesn't take much energy input to pressurize a liquid-filled container. Gases, on the other hand, are highly compressible, so you do have to exert quite a bit of energy to pressurize a gas-filled container.

   The net result is that if you had, say, a water-filled container pressurized to 1000 psi, and another identical container, this one filled with air and pressurized to 1000 psi, and dropped them both onto a hard concrete floor so that they ruptured, the water-filled container would crack open, and you'd have water all over the floor. The air-filled container would explode, and you'd have pieces of shrapnel flying around the room.

   It is for this reason that PVC and CPVC are okay for liquids and low-pressure gases, but not for high-pressure gases.

   -Steve

    

   
   

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   Edited 5/27/2008 11:46 am ET by saschafer

3. 
   RickL | May 27, 2008 06:52pm | #3

   After 30 years in the business of maintaining custom and factory woodshops I'm pretty much on top of the subject.

   First of all PVC isn't considered legal by OSHA for one of the reaons you mentioned. There is documentation.

   http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=20202

   There are ABS type plastics rated for airlines.

   http://www.nibco.com/assets/ChmairOvrw.pdf

   There is an aluminum alternative from Kaiser Compressor and Garage Pak.

   The alternatives cost more than iron pipe but are quicker to install.

   Why do people ask for answers on the web instead of consulting with a manufacturer??? In my experience you often have to ask several people at a company as some folks fake the knowledge and it's preferable to get some kind of documentiation. Personally I don't put much stock on the forum answers. I've seen too many answers like..."Well I don't have any experience with your question but here's my take on the subject..."

    

1. 
   AZMO | May 28, 2008 02:02am | #7

   RickL

   Thanks for taking the time to review my post, and for the concise response. My exact reason for asking the question was to prove my first instinct, don't do it. I did do a search for pvc applications, but could not find a document to confirm or deny. Several sites required payment for access to the data base.  The OSHA letter allows the use of PVC but in only if encased, which would be more than enough hassle.

   On the other issue, I find a lot of very sound advice on Knots. Many of the responders are engineers and are more than willing to offer service on electrical issues, motor windings, steel hardness and fabrication etc. Yes some advice you just ignore, but every single resondant to this inquiry had the same answer.  So keep posting, we need all the technical advice possible. In the end, most of do this for fun and as an expression of our creativity.

   Morgan                  <!----><!----><!---->

   -----------_o

   ---------_'-,>

   -------(*)/ (*)   http://www.EarthArtLandscape.com

4. 
   colebearanimals | May 27, 2008 07:32pm | #4

    

   Hi AZMO,

            I saw PVC burst when it was hit by a steel rod by my friend in his metal working shop. It can happen. Several months ago I plumbed my 2000 sq ft shop for air. Used 1/2" copper. Works great.

                                                                       Paul

   
   

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   Edited 5/27/2008 12:33 pm ET by colebearanimals

1. 
   AZMO | May 28, 2008 02:14am | #8

   Steve, Andy, Len, Paul,

   I will post for all here. Thanks, just checking my instinct also. DONT DO IT seems to be the logical thought. Sure would be easy, I will have to bust out the copper and do some sweating. I just hate working with iron pipe, I seem to find a few threaded shavings later when I don't have shoes on.....

   Morgan                  <!----><!----><!---->

   -----------_o

   ---------_'-,>

   -------(*)/ (*)   http://www.EarthArtLandscape.com

5. 
   Len | May 27, 2008 08:47pm | #5

   Don't do it. You've been working on your shop for 3 months and it sounds great.

   PVC isn't meant for gases. Other things to consider, PVC cracks it doesn't dent, UV (sunlight) degrades PVC making it more brittle. If you have a cutoff fire out of your saw and it strikes the PVC...

   Use 1/2 copper if you don't want to use iron.

   Len

   "You cannot antagonize and influence at the same time. " J. S. Knox

6. 
   andyfew322 | May 28, 2008 12:25am | #6

   I'd go with something like copper. It's a little more expensive, but a whole lot more safe.

    

   there's no need to reinvent the wrench