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DWV or no?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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DWV or no?

Unread postAuthor: balt11t » Mon Jun 15, 2009 1:44 pm

I have a simple spray 'n' pray gun mapped out and I'm ready to buy the parts, but I ran into a little snag. I've been researching a little bit and found that these type of guns only reach about 50 psi in the chamber. DWV, in theory, should be fine, but I was wondering if anyone could give some suggestions and if you recommend pressure rated pipe where you get it from. I'd prefer to stay off shopping on the internet, but I guess it could be done if it's absolutely necessary. Thanks!
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Unread postAuthor: MountainousDew » Mon Jun 15, 2009 2:45 pm

You won't have a problem with DWV fittings at first, but they will eventually fail... If you just go to Lowes or The Home Depot, you will be able to find all the parts you will need. Go to the plumbing isle and look around, you won't have a problem finding sch 40 pipe.
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Unread postAuthor: c11man » Mon Jun 15, 2009 2:51 pm

im guessing this is for a 3 or 4inch chamber?

either way if you keep it spray and pray dwv is strong enough.
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Unread postAuthor: daberno123 » Mon Jun 15, 2009 2:52 pm

MountainousDew wrote:you won't have a problem finding sch 40 pipe.


True, you can easily find Schedule 40 pipe, but its nsf-pw pipe you're looking for with an actual printed pressure rating on the side. Schedule 40 only designates wall thickness and most DWV pipe is Schedule 40. The difference is DWV is cellular core pipe, which basically means its like foam.

Try an irrigation store or look through the yellow pages for a plumbing supplier near you for pressure rated pipe. However, your local hardware store could carry it, the Lowe's near me carried pressure rated pipe up to 4".
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Unread postAuthor: balt11t » Mon Jun 15, 2009 2:56 pm

Okay, thanks for the quick reply. I do have one or two more questions. Should I try ABS for the splitting properties instead of PVC, which shatters? And what is the difference between Schedule 40 and Schedule 80?
To c11man: Yes, I was planning on having a 3 inch chamber and a 1.5 inch barrel. I'm trying to stick to a 1:1.5 volume ratio, so I'll figure out the necessary lengths as I move on
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Unread postAuthor: EphOph » Mon Jun 15, 2009 3:02 pm

If you are using DWV, then ABS is the better choice. The difference between schedule 40 and schedule 80 is the wall thickness of the pipe - a higher schedule number designates a higher wall thickness, and with it a higher pressure rating.
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Unread postAuthor: balt11t » Mon Jun 15, 2009 3:05 pm

Oh, thank you very much EphOph. Hopefully I can start shopping this weekend!
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Unread postAuthor: Biopyro » Mon Jun 15, 2009 3:50 pm

Just so you know, DWV ABS doesn't only have better failure characteristics. It is also much stronger than DWV PVC.

The ultimate would be HDPE, which creates lightweight strips when it does fail, but is really tough, so wouldn't anyway. It's hard to use though, because it has to be heat welded, and can't be glued.
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Unread postAuthor: mark.f » Mon Jun 15, 2009 5:35 pm

Just for clarification.

NSF-DWV and NSF-PW designations are just what the name says: National Sanitary Foundation ratings.

While NSF-PW is, way more often then not, pressure rated (be it fittings or pipe), why not actually go by the rating meant for reliability and strength.

Pipe will ALWAYS have a pressure rating printed on it if it is pressure rated. No dicking about with NSF or ASTM ratings required.

SCH-40 pressure rated PVC fittings will be printed with ASTM D2466. Period. You should also refer to the Wiki's guide on identifying pressure rated fittings.
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Unread postAuthor: Moonbogg » Mon Jun 15, 2009 7:41 pm

IMO...if I built another combustion cannon it would be cellcore ABS again, because the first one I made is plenty strong and much lighter than PVC. And my plastic cannon is a metered propane cannon, more powerful than a spray and pray.
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Unread postAuthor: Technician1002 » Mon Jun 15, 2009 8:26 pm

Biopyro wrote:Just so you know, DWV ABS doesn't only have better failure characteristics. It is also much stronger than DWV PVC.

The ultimate would be HDPE, which creates lightweight strips when it does fail, but is really tough, so wouldn't anyway. It's hard to use though, because it has to be heat welded, and can't be glued.


FYI, Cellular core DWV ABS has been pressure tested here.

http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html
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Unread postAuthor: balt11t » Mon Jun 15, 2009 8:32 pm

Thanks Technician1002, I'll check that out.
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Unread postAuthor: Biopyro » Tue Jun 16, 2009 3:38 am

And there was this oxy-propane cannon made from cellcore ABS too - just goes to show, it's tough stuff!

I made my first combustion from ABS, and it's holding up fine.
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ABS cellular

Unread postAuthor: Technician1002 » Tue Jun 16, 2009 4:11 am

I didn't find that one, but I found a spray and pray with a shot of Oxygen from a welding torch. I highly don't recommend this.

@Biopyro, that one was propane oxygen. Listed in the linked article.

[youtube]http://www.youtube.com/watch?v=WFGdK1YeuQw[/youtube]
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Unread postAuthor: jimmy101 » Tue Jun 16, 2009 1:18 pm

MountainousDew wrote:You won't have a problem with DWV fittings at first, but they will eventually fail...

Really? Seems to me that the vast majority of combustion gun use at least one DWV only part; the cleanout cap. Cleanouts aren't used in PWS systems, only DWV systems.

My first gun (metered & fanned) is pushing a decade old and has been fired hundreds of times and the cleanout has never failed. Heck the chamber is 3" cell core. For a basic combustion (or an advanced combustion at 1X), DWV is adequate as long as everything else is done properly.
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