Getting slack with DWV usage

Post questions and info about combustion (flammable vapor) powered launchers here. This includes discussion about fuels, ratios, ignition systems and anything else relevant to launchers powered by igniting things like hairspray or propane.

Postby fox_shooter2 » Thu Jul 27, 2006 8:29 pm

G'day everybody. I have been here a relatively long time (before chamber fans![:0]) and have seen countless topics come and go. I almost never get into discussions about the politics of the forum but I beleive there is something that needs to be addressed. Over the last few months I have seen a topic arise in many threads about the use of DWV PVC. I live in the DWV cannon capital of the world, Australia, so I have had a good few encounters with DWV launchers.

I am worried we are, as a comunity, supporting the use of a potentially dangerous medium. DWV is weaker than pressure rated PVC, no doubt, so why do we support its use? Many people here are inexperienced with solvent welding and cannon design. I am not saying DWV cannons will cause damage, they may or may not, but they do have a smaller safety margin (especially the fittings). With every cannon that causes bad publicity the more negativity is cast on our activities as spudders. I live in Aus, I know how a bad image affects how a groups activities can be regulated. It can mean the difference between a smile from someone or a police call.

I also realise that not all DWV components are created equally, granted some are obviously better built than others. I guess this is because standards are relaxed a little for non pressure PVC. DWV in Aus is absolutly no good for any cannon use! The caps blow APART, not off the threads but into pieces. The pipe has a far smaller wall thickness, I would not in good conscience say it was safe to built a DWV cannon. Other countries may have better DWV and here lies the problem, a new spudder may not be able to tell good DWV from bad. We, as specialist in the field, say "yes, DWV is good", can you see a problem?

Im sorry for the critical topic. I love being able to check the forums and see heaps of new people entering the hobby. We have worked so hard in the past to create a good image of safe and happy spudding, Why allow a shortcut to open a potential attack point. This is a discussion forum so any debate is good, I welcome your input. I hope everybody reads this and thinks about the subject, what are we risking.:?::?::?:

edit: anyone think this should go in general discussion?
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Postby markfh11q » Thu Jul 27, 2006 8:37 pm

We never say DWV is good. For pneumatics or, worse, hybrids, it is frowned upon.

On a combustion launcher, though, it's generally OK to use it, but it's recommended you use rated fittings anyway.

There's one thing you can't change usually on combustions. All cleanout caps are DWV or sewer rated, dont' have an ASTM rating, and are not pressure rated. Pressure rated plugs are good if you can find em. People should never have the cleanout cap pointing at anybody or themselves...
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Postby TurboSuper » Thu Jul 27, 2006 10:51 pm

I think 90% of the incidents that involve spudgun faliure are associated with improper solvent welding techniques rather than DWV fittings (the other 10% is people who use cellcore or thinwall).

Now I know that DWV fittings have a much smaller contact area than pressure-rated ones, but I can guarantee that if you were to look over the shoulder of any of these people while they're building, you will see they're doing something wrong.

People have taken DWV pipe and fittings up to 60+ PSI with no incident, combustions produce about 50 PSI.

Use primer , solvent weld properly, clean everything first, square the ends, dont screw the ignitor or other crap into the endcap, and the gun wont blow up on ya.
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Postby fox_shooter2 » Thu Jul 27, 2006 11:01 pm

We do have to account for improper construction, the unknowing public does. Would the incidence of cannon failure be reduced if DWV was not used? I dont know but there seems to be more failures now than a couple of years ago.

Can anyone move this topic into the general discussion section?
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Postby sgort87 » Fri Jul 28, 2006 12:23 am

I'm sorry Fox, but you have failed to funnel your argument into one specific idea and course of action. What exactly do you want and how do you want it done?

Edit: I think this should be in the Materials section if anything.
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Postby DK » Fri Jul 28, 2006 3:13 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Mr. Gort</i>
<br>What exactly do you want and how do you want it done?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

What he <i>wants</i> is to discuss the recent "laxness" towards DWV cannons being built. He says in Australia, the DWV components are very thin and that they fail. This is bad. However, other countries may have better (ie. thicker) DWV components than others. He wants to discuss this.

<i>How he wants it done</i> is to stop the "laxness" towards the use of DWV pipe and fittings and insist on using only pressure-rated PVC.

To sum it up: inexperience + DWV in Australia + cannon failure + crowd = BAD

Solution: NSF-PW use only :p


I agree and I do believe you're correct about the different types of DWV pipe around the world. Having lived in Mexico and built a potato cannon down there, I can personally vouch for the thinness of what they call (non-pressure) DWV pipe. You can poke holes in the fittings with a pen (no joke). I honestly doubt it would hold 20 psi for too long.

To build the cannon, I had to buy 'hydraulic pipe' <i>imported</i> from the US. It cost me almost <b>$200 CAD</b> to build a 24"x4" simple combustion cannon with an appropriate barrel. If I hadn't persevered and been so adamant about buying the pressure rated pipe, then I would have had to use the pressure rated DWV they had at the hardware store (please note that this is different from the DWV I mentioned earlier). Even for this I only found it in a small city.

Normally, the non-pressure DWV pipe is used in home construction and is encased in concrete when used, so there is no real need to have any thickness to the pipe or fittings. The commonplace DWV down there is cheap as hell, but I wouldn't think twice about not using it in a cannon.


<font size="-3">Edit: I also agree about this being in the Construction & Materials section
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Postby fox_shooter2 » Fri Jul 28, 2006 4:16 am

Forgive me for providing an incoherent point. I would LIKE to see the use of non pressure rated PVC shunned by this forum as it used to be (unless it is for non load bearing components). There is a safer (although more expensive) option that provides more forgiveness and increased safety. Safety should be our biggest concern.

I am sorry to those that have trouble locating high pressure PVC but all it takes is one uninformed person to stick a few too many srews through their chamber wall and cause an injury, and all the do gooders want spudding banned. DWV is LESS SAFE than pressure PVC (I just realized I sound like a whinging mother, sorry guys - but I still support my point).
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Postby Fez_uk » Fri Jul 28, 2006 5:00 am

yea if its a worldwide forum we should think if the wider perspective.

DWV in the Us isnt the same everywhere, so some new people may think oh they say dwv is ok for combustions I can make it out of that.

I know pressure rated is the best but not everyone does.
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Postby greeneyedboy5 » Fri Jul 28, 2006 8:33 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by markfh11q
[br]hybrids, it is frowned upon.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

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Postby benstern » Fri Jul 28, 2006 9:41 pm

I declare that people show go down to their local pvc store with ruler and camera in hand.
Take pictures of the open end of the pipe with a ruler across it!
Post them here so we can see worldwide differences in dwv pipe.
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