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any way around expensive fittings?

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any way around expensive fittings?

Unread postAuthor: isban » Sat Mar 03, 2007 6:32 pm

I recently got hold of about 2 feet of 8" pipe and wanted to use it for a combustion chamber. But I soon found that 8" fittings cost around $50 a piece. I was wondering if anybody had any ideas about different ways of sealing the back or reducing the size without spending so much dough. Any help would be greatly appreciated since all my friends really want me to make it.
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Unread postAuthor: imablackskater » Sat Mar 03, 2007 6:40 pm

you could get an eight inc cab made of cheaper material since it will be a combustion. but where did you find 8 inch pipe.
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Unread postAuthor: Hotwired » Sat Mar 03, 2007 6:50 pm

Seal the back off with a really thick wooden plug and a lot of screws through the pipe wall.

A rubbery glue round the edges before you push it in would help seal it a bit more but will make it difficult to remove the plug for maintenance.

Drill holes for fuelling and ignition. The fuelling hole needs to be sealable.
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Unread postAuthor: Fnord » Sat Mar 03, 2007 7:31 pm

Wouldn't it be really hard to get a good seal with wood? I know its not as important in a combustion but it would be kind of inconvenient. Also, Ive never seen pressure rated wood ;)

Maybe try pvc in sheets? If you can find any cheap.
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Unread postAuthor: frankrede » Sat Mar 03, 2007 7:51 pm

sgort did it with wood I believe.
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Unread postAuthor: LGM » Sat Mar 03, 2007 8:49 pm

This will sound crazy, but hear me out.
Make sure that the end of the chamber to be sealed is smooth, then find a large plate of wood or preferably PVC sheet (thin metal if need be), attach a hinge to the plate and chamber, and three spots on the chamber end to fasten the sheet to once it is closed.
Or you could bolt on a piece of light sheet metal.
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Unread postAuthor: Hotwired » Sat Mar 03, 2007 9:02 pm

Try forcing air through any structually sound plank and tell me how you get on.

A known pressure rating is too expensive for this, whats important is a good solid plug that will keep the back closed and not fly out. Hence the need for a a large number of screws and a big bit of wood.
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Unread postAuthor: isban » Sat Mar 03, 2007 9:20 pm

I was thinking pvc sheet too. The wood idea seems to be easy though and less expensive. For a reducer I've seen flexible black connectors with hose clamps on them. Would they be ok for a combustion? They are a lot cheaper than pvc.
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Unread postAuthor: Flying_Salt » Sat Mar 03, 2007 9:56 pm

I think those flexible black fittings are those Banjo fittings? I'm pretty sure they would work, people use them to make breech loading things. You may want to check if they're pressure rated though.
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Unread postAuthor: pyrogeek » Sat Mar 03, 2007 10:56 pm

Could you melt PVC down and like, cast a plug for the end? Either heat it up just until it becomes soft enough, or dissolve it in an acetone/MEK solution and mold it around the pipe?

Everyone here probably has PVC scraps lying around, so it shouldn't be a problem of getting the material cheap. Acetone isn't too expensive.
The only risks I can think of are the PVC catching fire while melting it and breathing in the fumes. Or it becoming brittle. Also, I'm not quite sure how strong the PVC will be when you dissolve it and let it resolidify.
So yeah, just an idea.
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Unread postAuthor: pyromanic13 » Sat Mar 03, 2007 10:59 pm

use screws to secure a plywood cap on and use the expanding "great stuff" to seal the cracks
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Unread postAuthor: noname » Sat Mar 03, 2007 11:05 pm

I don't think any of you realize just how huge 8" PVC is. I've got 20 feet of the crap and just today my friend and I started to cut it to size an make a propane meter for it. I e-mailed DR to see if he had any ideas, because he's built some huge cannons before, he hasn't replied yet. I'm pretty sure a plastics store near me will cut 8" cicles for me out of sheet PVC, but I'm not completely sure.

Oh, and by the way, be on the lookout for the finished product. The propane meter is a 3 foot long section of 3/4" steel.
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Unread postAuthor: isban » Sat Mar 03, 2007 11:32 pm

What kind of a store would cut the circles for you? I was thinking my only hurdle that was that I couldnt cut out 8" circles. Oh and I dont think the black flexible fittings are pressure rated, but they might still work.
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Unread postAuthor: noname » Sun Mar 04, 2007 12:24 am

<a href="www.tapplastics.com">Tap Plastics</a> gives me free stuff, or at least, really cheap. I bought a 6" x 6" square of 1/2" PVC sheet, which usually would be about $2.50, and they just gave it to me for free. I also wanted to buy
2 1/4" acrylic sheets
1 1/4" PVC sheet
1 1/2" acrylic sheet
whihc would've ended up about $10, and they gave me
4 1/4" acrylic sheets
4 1/4" PVC sheets
2 1/2" acrylic sheets (about 15 bucks worth of stuff total)
for $4.50.

I don't know why, they're just cool.
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Unread postAuthor: frankrede » Sun Mar 04, 2007 12:27 am

those black things are the definition of dwv, they can't take pressure or tehy will blow off. They are for water drainage.
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