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DWV Barrel?

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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Unread postAuthor: frigaardj » Sat Jan 07, 2012 9:13 am

Looked at all those sites, they're all stupidly priced.. I will stick to eBay for now. Might order a regulator tomorrow and try and sort out what PVC I need.

Out of curiosity do Reece's stock big pressure rated PVC (80mm+)? I am eyeing up something like that for a chamber, so I can put in a decent fan etc.
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 07, 2012 9:27 am

All DWV PVC 3"/80mm combustion cannon, never blew up :D the barrel/chamber are the same piece of pipe, I just added a wider section of pipe sleeve just in case it did decide to shatter.
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Unread postAuthor: Crna Legija » Sat Jan 07, 2012 9:52 am

frigaardj wrote:Out of curiosity do Reece's stock big pressure rated PVC (80mm+)? I am eyeing up something like that for a chamber, so I can put in a decent fan etc.


idk of they stock it but i know they'll get it for ya we ordered some 225mm pn18 pipe at work.
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Unread postAuthor: jimmy101 » Sat Jan 07, 2012 12:57 pm

frigaardj wrote:You suggest that I cut it off before the pinhole, as the pressure issue from that is not great enough?

Absolutely not! Why ruin a perfectly good torch head?

Just unscrew the air mixer and use a short length of hose and some hose clamps. (Heck you don't even really need the hose clamps.)
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6 months from now when a torch would be really handy you can just take off the hose, put the mixer back on.
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Unread postAuthor: SpudBlaster15 » Sat Jan 07, 2012 2:42 pm

I would presume that there is little pressure on the actual barrel as the force can be released on the tennis ball... and therefore a DWV barrel would be acceptable. Is this true?


That's not quite how fisiks works, as the pressure at all points in the launcher will be roughly constant at a given time step, but lightweight ammunition such as a tennis ball should act as something of a regulator and keep the peak pressure relatively low.

On the topic of Oz/NZ, do you know where to find a cheap propane regulator? I have looked in all the hardware stores, small ads, ebay etc...


You don't need a propane specific regulator; any unit designed to regulate air pressure (Not flow) will work for your fuel supply as well.

You suggest that I cut it off before the pinhole, as the pressure issue from that is not great enough?


A much better way to adapt a Bernzomatic torch head to a fueling system is to simply unscrew the curved brass piece and thread a 1/4" male compression x 1/4"NPT fitting in its place. You'll then be able to connect it to your regulator/hose fitting with NPT threads rather than some ghetto-rigged hose clamp setup.
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Unread postAuthor: jimmy101 » Sat Jan 07, 2012 3:14 pm

SpudBlaster15 wrote:A much better way to adapt a Bernzomatic torch head to a fueling system is to simply unscrew the curved brass piece and thread a 1/4" male compression x 1/4"NPT fitting in its place. You'll then be able to connect it to your regulator/hose fitting with NPT threads rather than some ghetto-rigged hose clamp setup.
Ghetto? For filling a syringe threaded fittings are way overkill. Even for a pressurized meter operating at an atm of so above atmospheric it is overkill. Plus, unscrewing the pipe with the meter hole in it is risky since it is often glued in place.
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Unread postAuthor: MrCrowley » Sat Jan 07, 2012 5:09 pm

frigaardj wrote:Out of curiosity do Reece's stock big pressure rated PVC (80mm+)? I am eyeing up something like that for a chamber, so I can put in a decent fan etc.
Yup, they should do. Reece's stock everything up to 110mm pressure rated PVC where I live, including 65mm and 80mm diameters.
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Unread postAuthor: SpudBlaster15 » Sat Jan 07, 2012 6:29 pm

jimmy101 wrote:Ghetto? For filling a syringe threaded fittings are way overkill.


You're probably right, for a syringe it would be overkill.

Even for a pressurized meter operating at an atm of so above atmospheric it is overkill.


For a regulated system such as what the OP has implied he wants to use, threaded fittings are easily the best option for attaching the torch head to the regulator. The connection will see the full vapour pressure of the tank, and needs to be as strong and well sealed as possible.

Plus, unscrewing the pipe with the meter hole in it is risky since it is often glued in place.


There is a small amount of medium strength threadlocker on the threads, but I've removed at least half a dozen of them and didn't have any problems.
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Unread postAuthor: frigaardj » Sat Jan 07, 2012 7:22 pm

Crna Legija wrote:we ordered some 225mm pn18 pipe at work.

Sounds good, looks messy :) I'll go for an 80mm-100mm chamber though :wink:

SpudBlaster15 wrote:There is a small amount of medium strength threadlocker on the threads, but I've removed at least half a dozen of them and didn't have any problems.

This idea is attractive as it eliminates the need for the hose barb etc, I could use some of that nice metal mesh hose with 1/4" fittings. Once I take off that bent piece of brass I would not be able to put it back on though (and not use it as a blowtorch)?

EDIT: how would this be as a regulator? Is it too cheap, too expensive?

http://www.ebay.com.au/itm/Air-Compressor-Pneumatic-Regulator-w-Pressure-Gauge-/230714933557?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item35b7ae8135
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Unread postAuthor: mattyzip77 » Sun Jan 08, 2012 5:51 pm

If its only being used for the barrel, than I wouldnt worry too much about it!!!
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Unread postAuthor: Crna Legija » Mon Jan 09, 2012 1:26 am

mattyzip77 wrote:If its only being used for the barrel, than I wouldnt worry too much about it!!!


I would if a round jams your stuffed.
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Unread postAuthor: frigaardj » Mon Jan 09, 2012 6:08 am

Crna Legija wrote:I would if a round jams your stuffed.

Yeah I agree, and now I know where to buy SCH40. Plus, I found a source for cheap tennis balls :)
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Unread postAuthor: frigaardj » Mon Jan 09, 2012 6:48 pm

MrCrowley wrote:Yup, they should do. Reece's stock everything up to 110mm pressure rated PVC where I live, including 65mm and 80mm diameters.

Are they reasonably priced? I am on a bit of a budget.
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Unread postAuthor: MrCrowley » Mon Jan 09, 2012 6:58 pm

If lucky they'll sell you it at trade price but for a student, they aren't exactly cheap. I think 1m of 65mm pressure rated PVC cost me like $40 and then $20 for a 65mm coupler (which I never used).
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Unread postAuthor: frigaardj » Mon Jan 09, 2012 7:02 pm

I called up the Stepney branch today and the guy quoted $10/m for 65mm class 12, and $35/m for 80mm class 12. Considering the relatively low cost of 65mm could I build the whole thing out of it?

Imagine if the chamber were 0.7 metres long and 65mm diam; would the gas be able to mix in a long and thin space like that? Would it take more than one fan perhaps?
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