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Thread: My New Pressure Chamber

  1. #1
    Join Date
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    My New Pressure Chamber

    THIS IS "NOT" A SUGGESTED METHOD. IT IS ONLY A NARRATIVE OF SOMETHING I MADE. ALL RISK IS MINE.

    I cast pen barrels on occasion and have always done the onesy towsy thing but I wanted the ability to cast multiple barrels on a 10 inch length of tubing in one shot so I made a long round mold out of 5/8ID PVC tubing. However the overall length of the mold did not allow use of my 2gal paint pot I normally use as a pressure pot for my castings. Needed something longer then the paint pot turned on its side. Three inch PVC to the rescue.

    The mold. Its about 13 to 14 inches long, in any case much longer then the depth of the paint pot. More on it in another post.
    IMG_3607.jpg

    A comparison of the new one to the paint pot.
    IMG_3575.jpg

    How it is mounted, the pressure end and the access end with the mold inside.
    IMG_3600.jpgIMG_3603.jpgIMG_3599.jpg

    I used a 3" clean-out adapter for the access end but could not get it to seal. Had two of the threaded plugs so used a section off the bottom of one and glued into the bottom of the thread female section to act as a seat for a gasket. The first pic shows the plug with the psa foam I used as a gasket. The second pic shows the trimmed down plug being used with PSA sand paper to sand the seat smooth.
    IMG_3583.jpgIMG_3592.jpg

    Installation of the seat. I took a saw kerf section out of the seat section so that it would collapse a little and go far enough down into the female fitting to allow the plug to use all of it's threads when screwed in. Glued the saw kerf together and filled the back side of the seat with PVC glue to seal it and keep it in place.
    IMG_3580.jpg

    The only negative to the assemble is that the clean-out is the only part that is not schedule 40 and is not intended for pressure use. However, it does have almost 1/8" deep threads and is nearly 1/4" thick through it's cross section. Although schedule 40 is rated at around 160psi I am running at most 70psi. I tested it to 80psi and noted no creaks or groans so I am not worried about it not holding up. It still leaks a little, drops from 60psi to 40 in about 30 minutes but with a compressor attached overnight that is not a problem.

    Appreciate all comments.
    Last edited by James Combs; 01-04-2017 at 8:17 PM.
    ____________________________________________
    JD at J&J WoodSmithing
    Owingsville, Kentucky

    "The best things in life are not things."

  2. #2
    I think it all looks interesting, but I don't know what a pen "barrel" is or why it needs pressure.

  3. #3
    Join Date
    Feb 2016
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    NE Iowa
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    If it's schedule 40 pipe (about 3/16" wall thickness for 3" pipe), the rated burst pressure is over 500psi, so you've got a lot of margin. You might blow the ends off well before that though, depending on the quality of your weld, so I'd stand to the side, not the front. ;-)
    Last edited by Steve Demuth; 01-27-2017 at 9:53 PM.

  4. #4
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    Modesto, CA, USA
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    Be aware that OSHA does not allow pvc for compressed air. when it fails it explodes and shrapnel flies everywhere. The old acid type fire extinguisher make good pressure vessels but I do not now how much pressure they can take.
    Bill D.

  5. #5
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    Missed seeing Dave's and Steve posts until Bill's bumped it to the head of the line again.

    Quote Originally Posted by David Freed View Post
    I think it all looks interesting, but I don't know what a pen "barrel" is or why it needs pressure.
    Dave, sorry about the late post back. By way of explanation for "pen barrel", many wood workers/turners also make ink pens. We refer to the upper and lower round sections as barrels. Pens can be made(turned) from wood but some of us also cast the "barrels" from acrylic resin, a liquid plastic that can be hardened by mixing it with a designated hardener. The pressure chamber prevents the appearance of air bubbles in the casting while it hardens. Some resin examples are polyester resins like Casting Craft and Simar41. Polyurethane resins like Alumilite are also used. You won't find a lot of turned pens here on SMC but there are a few. Here is an example by Ben Gastfriend from 2009, it shows a two barrel pen made from Cocobolo. Most folks that turn pens are also members of the IAP, International Association of Pen Turners over on penturners dot org. If you are interested in seeing more on casting with pressure chambers that's the place to go, especially check out their library. BTW here is a pic of a casting for a pen I made recently. The upper barrel is a clear casting over a label that pictures a peacock feather.
    CaneFeather (0).jpg
    Appreciate you looking and your comments.

    Quote Originally Posted by Steve Demuth View Post
    If it's schedule 40 pipe (about 3/16" wall thickness for 3" pipe), the rated burst pressure is over 500psi, so you've got a lot of margin. You might blow the ends off well before that though, depending on the quality of your weld, so I'd stand to the side, not the front. ;-)
    Steve, same as with David, sorry I missed your post. What you are saying is pretty much the way I looked at the PVC. I had looked up the specs and found similar ratings and even higher burst ratings so I feel pretty safe at only using ~60psi. Appreciate you looking and your comments.

    Quote Originally Posted by Bill Dufour View Post
    Be aware that OSHA does not allow pvc for compressed air. when it fails it explodes and shrapnel flies everywhere. The old acid type fire extinguisher make good pressure vessels but I do not now how much pressure they can take.
    Bill D.
    Bill Thanks for bucking this back to the top of the line, had forgotten about it, always try to acknowledge folks posts i my threads. Yes I am ware of the OSHA regs on air and PVC but a that pressure I am using I am not concerned. Had a similar comment on another forum that I posted the same thread on. Really appreciate the thoughts though and thanks for looking and commenting.
    ____________________________________________
    JD at J&J WoodSmithing
    Owingsville, Kentucky

    "The best things in life are not things."

  6. #6
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    693
    500 PSi burst pressure. sounds like plenty of safety margin. I think the pvc failures are from pipe at least 10-20 years old with many daily pressure cycles on it.
    Bill D.

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