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Bell reducers

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Bell reducers

Unread postAuthor: fishyfish777 » Mon May 26, 2008 10:31 am

Well, hello Spudfiles. This is my first post.

I heard bell reducers are the first thing to go wrong in a pneumatic cannon because they are not pressure rated. About safety on this item:

I am making an in-line version of a pneumatic spud gun. :wink: My first one. Plans:

Image

So, since how you usually pump (the hose from the bike pump) would be like the next picture, it would be safe to assume the cone of the explosion would be in front of me, and I'd be almost perfectly safe, correct?

Image


Just... This is my first spud gun. I planned it out using free time in school (high school) and some guy's idea on youtube (I forgot who, sorry).

Criticism accepted.
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Unread postAuthor: psycix » Mon May 26, 2008 10:47 am

When solvent welding pvc, the two parts become one, and chance is that your whole chamber shrapnels up....
Your "field of explosion" will become 360 degrees if that happens.
Just dont use a bell reducer.

I dont know the lengths of your chamber/barrel, but your chamber seems way overkill to me.
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Unread postAuthor: jimmy101 » Mon May 26, 2008 12:10 pm

I agree with psycix. If a gun fails stuff goes in all directions. In your drawing the chamber would be going in the opposite direction of your "field of explosion" (for every action there is an equal and opposite reaction).

Besides, if the gun is going to fail it will probably do so when you grab the ball valve and start to twist it, not when you are pressurizing the chamber. When operating the valve you are within inches of the point of likely failure.
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Unread postAuthor: jrrdw » Mon May 26, 2008 1:17 pm

The bell reducer has short sockets. Not enough gripping range. Since this is your 1st spud gun I recomend the Small Inline Pneumatic Kit
click here You still have to put it together and comes with full instructions and all the parts you need.

Welcome to Spudfiles.
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Unread postAuthor: MrCrowley » Mon May 26, 2008 2:12 pm

I'd recommend you just go straight to sprinkler valve. Ball valves are awkward, slow, inaccurate etc.

Sprinkler valves are loads more fun and powerful. They only cost a few bucks more. They're piss-easy to mod also.

Read these:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC
http://www.spudfiles.com/forums/modding ... -t305.html
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Unread postAuthor: fishyfish777 » Mon May 26, 2008 6:11 pm

Okay...

can't find a god-damned thing at Lowe's. Made a little reducer... well, big, by putting a 1 - 1/2" reducer in a 1 1/2 - 1" reducer in a 2 - 1 1/2" reducer.

well, thanks psycix for a very good point there, but the wall of the bell reducer would be easier to breach than the wall of the compression tank AND the wall of the bell reducer, so I really doubt your point, but maybe you are right. I'm cementing two halves (well, I cut it at the base of the end cap) of the tank together after my little schrader valve pops in the tank and I can do nothing about it, except sawing the tank in half and reattaching the halves. I tried to get the end cap off, but it was really STUCK.

I had a little pipe of pvc, so I might cement-melt it and smear it on for extra strength there, and use duct tape too.. Is that OK, or is that going to make a major weak-point that will be the first to explode?

I think it is a major weak-point, but if I smear PVC-cement into the cracks, will it work?
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Unread postAuthor: jrrdw » Mon May 26, 2008 7:07 pm

I had a little pipe of pvc, so I might cement-melt it and smear it on for extra strength there, and use duct tape too.. Is that OK, or is that going to make a major weak-point that will be the first to explode?

I think it is a major weak-point, but if I smear PVC-cement into the cracks, will it work?


NO. That will not work.

Here is where you need to do some really good researching. Click on the Wiki button and when you get to the Wiki, do a search on 'solvent welding'.
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Unread postAuthor: TurboSuper » Mon May 26, 2008 7:10 pm

Can you find what you're looking for in copper/steel pipe? Those dimensions aren't that large, and any copper/steel pipe will be good up to a few hundred PSI.
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Unread postAuthor: jr » Mon May 26, 2008 8:07 pm

I would also like to note that your shrader valve needs/should be located in a place where there is 2 layers of pvc, like the side of the end cap not in the end of the cap.. more pvc for the threads to hold on too.
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Unread postAuthor: psycix » Tue May 27, 2008 7:26 am

fishyfish777 wrote:Okay...

can't find a god-damned thing at Lowe's. Made a little reducer... well, big, by putting a 1 - 1/2" reducer in a 1 1/2 - 1" reducer in a 2 - 1 1/2" reducer.

well, thanks psycix for a very good point there, but the wall of the bell reducer would be easier to breach than the wall of the compression tank AND the wall of the bell reducer, so I really doubt your point, but maybe you are right. I'm cementing two halves (well, I cut it at the base of the end cap) of the tank together after my little schrader valve pops in the tank and I can do nothing about it, except sawing the tank in half and reattaching the halves. I tried to get the end cap off, but it was really STUCK.

When glueing pvc, two pieces become one - they melt together at molecular level.
When pvc breaks, you should imagine it going like "safety glass" or "tempered glass" windows. One crack, and all breaks.
Video of a big sheet of glass breaking:
[youtube]http://youtube.com/watch?v=eqV5W76U8Qg[/youtube]

Thats what happens to your pvc, but then with shrapnel flying at high speed.
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Unread postAuthor: dongfang » Tue May 27, 2008 1:57 pm

Hi,

Just a comment: In Europe (at least) there are pressure rated bell reducers, e.g. the babes on page 19 here: http://www.wacon.de/stock/service/cepex/PVC%20Pressure%20Fittings%20TC%20v2.pdf.

The OP has no location in his profile (well OK he mentions shopping at Lowe´s...) - anyway the "bell reducers are unsafe" rule is not universal.

Regards
Soren
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Unread postAuthor: MrCrowley » Tue May 27, 2008 3:01 pm

dongfang wrote:Hi,

Just a comment: In Europe (at least) there are pressure rated bell reducers, e.g. the babes on page 19 here: http://www.wacon.de/stock/service/cepex/PVC%20Pressure%20Fittings%20TC%20v2.pdf.

The OP has no location in his profile (well OK he mentions shopping at Lowe´s...) - anyway the "bell reducers are unsafe" rule is not universal.

Regards
Soren

You can get them online in America too. It's just generally accepted the member wouldn't know about them if they're asking how to make a cannon.
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