SpudFiles

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.

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.

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.

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.

sgort did it with wood I believe.

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.

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.

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.

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.

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.

use screws to secure a plywood cap on and use the expanding "great stuff" to seal the cracks

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.

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.

<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.

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