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How-To: Make a pneumatic cannon with a 2" piston valve.

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Unread postAuthor: MrCrowley » Mon Apr 14, 2008 2:05 pm

Hmm weird, mine completely thread together. :?
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Unread postAuthor: niglch » Mon Apr 14, 2008 8:20 pm

MrCrowley wrote:Hmm weird, mine completely thread together. :?

I just bought some new parts to replace the ones I broke. The first is a 2" female adapter and the second is a 2" threaded plug. Both parts indicate that they are pressure rated & schedule-40 (NSF-PW). However, when I tighten them with my hands, the two parts only thread about halfway in before they lock up. Trying to force it in any more is what broke the last set of fittings I had. Is this ok or am I supposed to use some sort of lubricant when threading the parts together? I read online something about it being bad to over-torque PVC fittings so should I just leave it how it is?

Thanks.
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Attachments
fittings_2.jpg
Here are the two fittings separately.
fittings_1.jpg
The fittings only thread together this far before locking up . . . :(

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Unread postAuthor: MrCrowley » Mon Apr 14, 2008 10:28 pm

Yeah don't over-torque them.

The fittings I used were a female and male threaded adapter. They completely threaded together with ease.
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Unread postAuthor: clide » Tue Apr 15, 2008 5:07 pm

Fittings in the US shouldn't thread all the way together. The only ones I have seen that do have gaskets on them and aren't very common or are DWV parts.

PVC manufacturers typically recommend one to two turns past hand tight, and that seems to work for me usually.
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Unread postAuthor: MrCrowley » Tue Apr 15, 2008 10:43 pm

Yeah that's a good point Clide. I'm using metric fittings.
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Unread postAuthor: DaGrimRaper » Sat Apr 26, 2008 9:39 pm

wow thnks dude.
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Unread postAuthor: tony48 » Sun May 04, 2008 3:11 pm

Where did you get your barrel? I'm looking for a golfball barrel and I think I might have to go to a plumbing store to get one.
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Unread postAuthor: JDP12 » Sun May 04, 2008 3:26 pm

http://www.bcarms.com

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Unread postAuthor: THUNDERLORD » Fri May 23, 2008 1:07 am

Great How-To, Thanks MrCrowley.
Been thinking about piston design/ GB pistons and this will be very helpful.

Also with your system of having a seperate fill and exhaust pilot it looks like a way to add an auto-fill by leaving the fill attached.

I would like to design something similar with electric solenoids some time.
I read over the replies but didn't see any comments about that?
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Unread postAuthor: MrCrowley » Fri May 23, 2008 1:17 am

Yes, sometimes I leave my compressor attached if i'm shooting in the garage or driveway. I should've put a breechloader on it, maybe even a manual hopper*. Don't think anyone brought up anything like that, any questions just ask.

I'm in the process of building a new 2" piston golfballer for a school assignment, should be done in a week or two. I learnt a lot from this cannon, so i've made a few advancements in my new one. I could make it more powerful then it would be, but i'm limited by my assignment unfortunately. So I don't have 100% freedom.


*As in manual I mean that you need to do something to make the next golfball drop down, otherwise half of them will get sucked out in one shot.
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Unread postAuthor: drunkii » Sat Jul 19, 2008 9:25 am

how much did that cost you ?:p
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Unread postAuthor: MrCrowley » Sat Jul 19, 2008 5:16 pm

~$350NZD


Something like that
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Unread postAuthor: jon_89 » Wed Nov 12, 2008 1:19 am

I figured I ask this here instead of starting a new topic. I have read several topics of people using 1.25in caps and couplers as pistons. How well do these fit in 2in pipe?
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Unread postAuthor: MrCrowley » Wed Nov 12, 2008 3:08 am

In NZ I tried using them, all the same brand, but they were a few mm off.

I hear different brands have different outside diameters, so i'd recommend taking a small piece of 2" pipe to Home Depot and trying some 1.25" couplers out.
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Unread postAuthor: jmccalip » Wed May 13, 2009 6:09 pm

niglch wrote:
MrCrowley wrote:Hmm weird, mine completely thread together. :?

I just bought some new parts to replace the ones I broke. The first is a 2" female adapter and the second is a 2" threaded plug. Both parts indicate that they are pressure rated & schedule-40 (NSF-PW). However, when I tighten them with my hands, the two parts only thread about halfway in before they lock up. Trying to force it in any more is what broke the last set of fittings I had. Is this ok or am I supposed to use some sort of lubricant when threading the parts together? I read online something about it being bad to over-torque PVC fittings so should I just leave it how it is?

Thanks.


Yeah, just thought I'd add that anytime you see "NPT" thread(nation pipe thread), it means it's tapered. Like this:

Image

I'm not sure exactly why they taper the threads. At first I thought it might be easier to insure a leak proof fitting in case of tolerance errors in the the manufacturing process. But I work in a machine shop, and NPT threads tolerances for our parts are +-.0005 on how far the gauge threads.

Pretty much any plumbing/air supply pipe or fitting you buy in America is NPT. I guess we have to do things different from you NZ and AUS folk. :lol:
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Last edited by jmccalip on Wed May 13, 2009 6:13 pm, edited 5 times in total.
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