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Metered Mapp gas Potato gun

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Metered Mapp gas Potato gun

Unread postAuthor: fom » Tue Dec 26, 2006 7:57 pm

Well, this is my 3rd potato gun, im only 13 by the way :P
Spudblaster blaster gave me the C:B ratio and a few types but I did like 90% of it by myself, it has a 6 foot barrel and 16" chamber with over/under config. 80mm CPU fan on 18 volts, double spark gaps with metered mapp gas.

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Unread postAuthor: beebs111 » Tue Dec 26, 2006 7:59 pm

what do you use for an ignition source? im not familiar with abs, but maybe thats just painted........many of those parts are not pressure rated
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Unread postAuthor: PVC Arsenal 17 » Tue Dec 26, 2006 8:04 pm

^ ^ It's a combustion, no big deal.

You did a good job by the way. Not bad at all.

Is that ABS, because I've never seen yellow primer for PVC before...
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Unread postAuthor: SpudBlaster15 » Tue Dec 26, 2006 8:07 pm

Beebs, its a combustion gun, the parts do not need to be pressure rated. Solid core ABS will easily withstand the 40 - 60psi momentary pressure spike associated with the combustion of Mapp gas in air.

Very nice gun.
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Unread postAuthor: fom » Tue Dec 26, 2006 8:08 pm

PVC Arsenal 17 wrote:^ ^ It's a combustion, no big deal.

You did a good job by the way. Not bad at all.

Is that ABS, because I've never seen yellow primer for PVC before...


Thanks, and yes its ABS/

and beebs i use a eletric grill ignitor, switching to the red button piezo elecrtic device soon though.

Thanks for the comments.
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Unread postAuthor: beebs111 » Tue Dec 26, 2006 10:07 pm

i know that it is a combustion, thats why asked what he used for ignition duh! and i like to only use pressure rated pvc parts with my guns, just for safteys sake, even when it is only a combustion, very nice job
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Unread postAuthor: fom » Tue Dec 26, 2006 10:09 pm

beebs111 wrote:i know that it is a combustion, thats why asked what he used for ignition duh! and i like to only use pressure rated pvc parts with my guns, just for safteys sake, even when it is only a combustion, very nice job


The ABS im using is sch 40, but thanks for the comment
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Unread postAuthor: PVC Arsenal 17 » Tue Dec 26, 2006 10:31 pm

Yes, but your parts are DWV (drain waste vent) and are unrated. Sch 40 is only a measure of wall thickness I believe. You can tell if a pipe or fitting is pressure rated if it is marked with NSF-pw.
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Unread postAuthor: SpudBlaster15 » Tue Dec 26, 2006 11:13 pm

Who cares? It is a freaking combustion gun! DWV ABS can easily withstand the pressure spike, and is in fact far superior to pressure rated PVC in our (fom and I) cold Canadian climate.
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Unread postAuthor: fom » Tue Dec 26, 2006 11:45 pm

PVC Arsenal 17 wrote:Yes, but your parts are DWV (drain waste vent) and are unrated. Sch 40 is only a measure of wall thickness I believe. You can tell if a pipe or fitting is pressure rated if it is marked with NSF-pw.


I can name many advantages with ABS over PVC, and I think that the SCH means the psi, 40 SCH is 200 psi and 80 SCH is 400 psi
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Unread postAuthor: mark.f » Wed Dec 27, 2006 7:21 am

Nice gun! Good to see another fan of MAPP gas as well.

BTW, do you have the same problem I got with MAPP gas? After firing, the cleanout cap locks up so tight you gotta get a jar opener to get it off? This happens to me every time I fire.
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Unread postAuthor: Scope » Wed Dec 27, 2006 11:21 am

SCH means the thickness... but a bigger SCH will have a higher psi rating... but it depends on the pipe...

Nice gun!!... i like mapp

Guys can we leave the abs vs pvc thing alone... he didnt post his gun here to listen 2 evreyone fight over it agian
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Unread postAuthor: CS » Wed Dec 27, 2006 2:36 pm

To clear things up the 'sch' [schedule] only indicates the wall thickness, it in no regards defines the strength of such. More likely then not you have sch 40 cellular core ABS, which does not carry a pressure rating, and more so it is not intended for pressure. Although it is commonly accepted for use in launchers. Many people, including myself can safely say that they've put 1G rounds threw such guns without failure.

One first has to determine with whatever material it may [PVC, ABS] be if it in fact solid core, cellular core, or some other variant.

"I can name many advantages with ABS over PVC, and I think that the SCH means the psi, 40 SCH is 200 psi and 80 SCH is 400 psi" ~fom

It should be understood by other users that those numbers are 100% wacked. First the first stipulation of this all is you must first determine which material such is, and its cross section [cell core, solid]. Even from there the diameter of the pipe effects the pressure rating. So you cant emit pressure ratings without first regarding changes in diameter of it differences in cross section terms.

"Guys can we leave the abs vs pvc thing alone... he didnt post his gun here to listen 2 evreyone fight over it agian" ~Scope

First I wouldn't consider any such discussions 'fights', rather a convincing of the bull headed. Such discussions take place so that users involved in the conversation, and other forum drifters don't pick up false info because someone is spewing incorrect facts out of there ass. The discussions are simply not at yours, or the posters will to avoid as it is done for safety of forum members. Remember this forum doesn't revolve around you ;-)

Anyway to the gun itself, nothing overly complicated, while nice. Possibly could have been a bit more careful what appears to be yellow ABS glue? You also may have wanted to mount the batteries and such inside enclosure of some sort, as well decided on one type of metal for the metering system. You used all 3 hardware available metals brass, black, and galvanized. Also to turn the gauge in ~1/2 turn as currently the pressure gauge is pointing in the opposite direction of the user. Understand I'm being overly critical for your sake, as this launcher appears to be very fun. Simplest tend to be the 'funnest'.
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Unread postAuthor: Scope » Wed Dec 27, 2006 4:03 pm

I hear ya Pimp... I just feel bad for people who post cannons only to have a the thread get pulled away from there cannons...
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Unread postAuthor: fom » Sat Dec 30, 2006 6:57 pm

Thanks for the comments, and @ pimp my hardware store isnt that big so I had to use what they had, and the pressure guage is like that because my dad won't let me hold it so I place it on a angle.
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