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Hello and DWV

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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Hello and DWV

Unread postAuthor: bijoon » Mon Mar 16, 2009 10:19 pm

Hi, I have lurked this forum and other sites for years now. I haven't built a spud gun in over a year now and kind of got out of the whole scene. Now I am considering building a simple combustion for a friend. I have always built simple combustion launchers with the most powerful fuel used being mapp gas. I have always used fittings from home depot (dwv). I remember even two years ago there was a debate on whether or not dwv was safe. I returned tonight and searched through the forum and people are still debating it. What a disapointment, I was hoping I could get a clear cut answer. This time around I want to make sure things are completely safe because this launcher is for someone else. Maybe a clear cut answer is out of the question.

TLDR
So my question: "Is DWV safe for simple combustion launchers?"

I'm talking about deodorant and maybe mapp gas.
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Re: Hello and DWV

Unread postAuthor: starman » Mon Mar 16, 2009 10:35 pm

bijoon wrote:So my question: "Is DWV safe for simple combustion launchers?"


Yes it is. However, I would still steer clear of cellular core pipe. This means you may have to find your pressure rated larger pipe (3" and 4") some place other than Home Depot or Lowes. You can still find pressure rated pipe 2" and below at these places.

Welcome to Spudfiles! We'll be looking forward to seeing your cannon creation.
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Unread postAuthor: King_TaTer » Mon Mar 16, 2009 11:13 pm

If you want to make sure it's safe just make sure all your fittings say "NSF-pw" on them. This means that they can handle pressure and I can assure you 99.9% that it won't fail.

Combined with 2 and a half years of knowledge from this Forum and much personal experience I have never seen a simple combustion with pressure rated parts fail. This excludes breaks from exposure to the weather and operation in cold temperatures. As long as you know what your doing when constructing and solvent welding you/your friend will be fine.
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Unread postAuthor: TwitchTheAussie » Mon Mar 16, 2009 11:41 pm

I stand by whats been said already. The only problem Ive had personally with DWV is that I didnt glue it together properly. Other than that stay safe and happy spudding.
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Unread postAuthor: inonickname » Tue Mar 17, 2009 2:31 am

In a simple, 1X combustion you probably will not have a mishap with DWV if you treat the gun with due care. That said, if pressure rated piping (it can be nsf-pw or nsf-dwv, pw only means potable water) is available to you at average prices you should use it.

If I were building a gun for somebody else, I'd make sure I used safe materials, instructed them on proper use and tell them what's safe and what isn't.

To sum it up, if you don't drop your gun, only use "standard" fuels, don't leave it in the weather DWV will probably be fine in a 1X combustion.
-It's up to you to exercise what precautions you think necessary

Good luck, hope he likes his gun.

Edit:

welcome to spudfiles
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Unread postAuthor: Lentamentalisk » Tue Mar 17, 2009 2:48 am

The only problem I ever had with DWV was that the hairspray started to gum up the treads on the cleanout, so when I fired it, the plug blasted out, and left a huge burnt hairspray stain on my sweatshirt.
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Unread postAuthor: psycix » Tue Mar 17, 2009 10:53 am

Welcome to spudfiles!

For a spray n pray gun, DWV is acceptable and wont blow up, and even if it does, you'll just walk away with a burn. Nothing serious.
For highly advanced combustion guns (chamber fan, multispark gap, propane injection, possible burst disks) DWV is not very wise to use.
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Unread postAuthor: TurboSuper » Tue Mar 17, 2009 12:56 pm

DWV ABS is also safer than DWV PVC (better failure characteristics and impact resistance).
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Unread postAuthor: psycix » Tue Mar 17, 2009 4:16 pm

Well, depends what you call safe.
ABS fails relatively unharmful compared to PVC, but PVC usually fails at a higher pressure.
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Unread postAuthor: inonickname » Wed Mar 18, 2009 2:39 am

While you will probably be fine with DWV, do not use cellcore abs! before it is pushed through a die (correct word?) many small bubbles are whipped through it-making it very lightweight but very weak. Avoid it.

And yes, clarifying from above.

At a similar price PVC will usually hold more pressure but will shatter; abs will just split.
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Unread postAuthor: covey12 » Wed Mar 18, 2009 8:30 am

the only thing abs pipe is good for is a pneumatic cannon barrel, and pvc is still a better choice for that too
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Unread postAuthor: SpudBlaster15 » Wed Mar 18, 2009 11:33 am

covey12 wrote:the only thing abs pipe is good for is a pneumatic cannon barrel, and pvc is still a better choice for that too


No, ABS is MUCH better for high pressure pneumatic cannon barrels. DYI used an ABS barrel on a 500psi burst disk launcher for dozens of shots without failure. Had the material been PVC, it would have shattered to pieces on the first shot. ABS (even unrated) is also a superior material for combustion cannon construction. It is a much tougher material, is much less brittle, and has a much wider operating temperature range.

I would never build a combustion cannon from PVC, but for low to medium pressure pneumatics, pressure rated pipe is a must, and as rated ABS is extremely rare, PVC is is a better bet.
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Unread postAuthor: starman » Wed Mar 18, 2009 12:07 pm

SpudBlaster15 wrote:I would never build a combustion cannon from PVC


I'm a little surprised to hear a broad statement like that coming from you. Why not? I know ABS is much more attainable in your area of the great frozen Northland.

Otherwise, properly constructed, cemented and used, sched 40 or better PVC 1x combustion cannons are safe.
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Unread postAuthor: SpudBlaster15 » Wed Mar 18, 2009 12:33 pm

I'm not saying that PVC combustion cannons are unsafe. ABS is just the better option, mostly due to my climate. For at least 5 months of the year, PVC cannons are unsafe to use due to the cold. PVC is also extremely expensive in large pressure rated sizes, so given the choice between DWV PVC and DWV ABS, the choice is clear.
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Unread postAuthor: Moonbogg » Wed Mar 18, 2009 2:14 pm

I built an advanced combustion with cellcore ABS pipe and it hasn't failed. I am confident that it is solid after using is a while. Besides, it tends to crack rather than shatter even if it does fail. I struggled with this DWV question before building my gun as well, and now i'm confident it is just fine. I use propane, however, I would not use anything stronger, not even mapp even though its not THAT much stronger than propane. Thats just me though.
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