An Ignorant Combustion Question

[Evan]

I'm planing on making my first cannon and was just wondering if there was a rule of thumb for sizes of chamber to size of barrel. I don't mean the volume ratio but I mean like you have a .75" barrel, what size chamber would people sugest? or is it trial and error?

[CS]

Larger or the same as that of the barrel. I personally just go with a larger sized chamber to cut back on the length of the chamber. Im also sure that long skinny chambers may produce a decrease in performance. So I would suggest a 2" or 3" chamber. Although the C:B ratios should be kept in mind...

[Evan]

Hmm, I was thinking like 1.5 but mebe ill go 3" since i have that lying around anyways. (Just build new house and did plumbing ourselves so lots of leftover pvc )

[carlbelcher]

Use care with leftover PVC, make sure it Sch.40 and NOT DWV. If it’s not Sch.40 you can expect it to blow up in your hands.


EDIT:

Sorry, I meant to say "NSF DWV". I know you can use less than sch40 but why risk it. I don't like flying razor sharp PVC!

[rna_duelers]

Nah DWV is fine for combustion,i've only had one failure and that was a cap blowing out.It's fine by me and alot of other members to use DWV on combustion and all that worrying goes out the window the first time you see a spud air born with your own creation..hehe

[sgort87]

SCH40 IS NOT A STRENGTH RATING!!!! Schedule ratings are ratings of thickness.

There are plenty of fittings that are both schedule 40 AND DWV and they are fine for combustion launchers.

The Thin-wall DWV (Schedule 20) is NOT ok for combustions.

The pressure rated fittings we like to use are indeed schedule 40, but are also given the rating NSF-PW. Look for the PW if you want pressure rated fittings. If you are making a combustion then any sch 40 fitting is fine PW or DWV.

[frogy]

Note: this will be an off topic not, but nontheless %100 important:
If you do make a pneumatic don't buy NSF-DWV fittings for it from Home-Depot if they don't sell the fittings you need in NSF-PW buy your fitting off of http://www.PlumbingSupply.com

[Atlantis]

My cannon has a Sch30 chamber, I picked up the 3"sch30 to 1.5"sch40 adapter purely by luck. I would never use propane with Sch30 though, it's somewhat thin.

[Evan]

Ok so 3" sch 40 is good for chambers, right? also purple primer + regular Oatey pvc cement is fine if I don't care about looks?

[spudshot]

if its got a pressure rating, yeah its fine, if it says cellular core then no, its not