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2.5" Dust valve cannon advice please.

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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2.5" Dust valve cannon advice please.

Unread postAuthor: DashVT » Sun May 19, 2013 5:18 pm

Hi,

Alright first post here.

If this post is not right place I apologize. So I am planning on building a cannon for a physics final project utilizing a 2.5" Mecair VEM220 Dust Collector diaphragm valve and a 2.5" barrel for tennis balls.

I found the Mecair valve after many hours of searching when I wasn't able to get a Supah Valve but this seems like it might be a better option anyway. I haven't found a lot of info about this type of valve for spud guns.

Here is the valve: http://www.gekko-inc.com/store/diaphrag ... em220.html

And some info about the Mecair 200 series:
http://www.cleanairsystems.com/attachme ... Series.pdf

My questions:
1) Is this definitely my best option? Or are their other plug and play piston valves or a different brand or model of Dust Collector valve that would be better or cheaper?

2) How should I pilot the valve? Its already a double diaphragm valve (smaller diaphragm pilots primary valve). On the info page above is says the VEM type valves have "Remote pneumatic connection" rather than an integrated solenoid.

Could I possible just drill and tap a blowgun into the secondary diaphragm valve? Or is there a better option?

2) What would you recommend for barrel and chamber sizes for best performance firing tennis balls?


Thank you very much for your time I would love to hear from anyone with experience with this type of project!
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Unread postAuthor: jsefcik » Sun May 19, 2013 9:16 pm

For barrel im pretty dam sure sch40 2.5 inch (electrical conduit fits tennis balls perfectly:)


If its the same as a 1.5 inch dust collector you should be able to just put a ball valve ns quick connect right into the top part of the valve:)
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Unread postAuthor: millons70 » Sun May 19, 2013 10:42 pm

Well, a lowes I went to that sold the 2.4inch electrical conduit did not fit tennis balls at all. I bought my barrels from flexpvc.com I don't have acces to any other place in my area...
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Unread postAuthor: jsefcik » Mon May 20, 2013 6:21 am

Was it schedule 40? Check spudtechs website,, the conduit I got from my lowes fits
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Unread postAuthor: jackssmirkingrevenge » Mon May 20, 2013 1:04 pm

Could you tell us a bit about what you want to achieve with the project? Maximum performance, repeatability in terms of accuracy or range, semi-automatic fire?
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Unread postAuthor: DashVT » Tue May 21, 2013 12:27 pm

Thanks everyone for the replies!

Could you tell us a bit about what you want to achieve with the project? Maximum performance, repeatability in terms of accuracy or range, semi-automatic fire?


I would prioritize power, repeatability, and accuracy. I really like the idea of being able to hit a target at a high angle of fire. I will be using this as my high school physics final project to study projectile motion among other relevant topics. I will be limited to 40 PSI for at-school use but the maximum working pressure of the valve is 125 so I would like to build the whole cannon to that spec.

I don't really have the time right now to work on a semi-auto.

Also, I found that the Mecair VEM220 won't be available in my timeframe of a few weeks so I'll have to use the more expensive but higher performance Goyen RCA62T, but this shouldn't make any difference in the design.

Thanks again
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Unread postAuthor: jackssmirkingrevenge » Tue May 21, 2013 12:36 pm

I would go for solenoid piloting, it's really the best way to ensure repeatable firing, along with an accurate chamber filling gauge.
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Unread postAuthor: Technician1002 » Tue May 21, 2013 7:21 pm

Add a metering orifice and tube for dead space to your meter. The ~20mS discharge times on my cannon caused the needle to bend. Save your meter from rapid decompression.
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Unread postAuthor: jackssmirkingrevenge » Wed May 22, 2013 12:10 am

Technician1002 wrote:Add a metering orifice and tube for dead space to your meter. The ~20mS discharge times on my cannon caused the needle to bend. Save your meter from rapid decompression.


... or simply put it after a ball valve that is closed before firing :)

I really like the idea of being able to hit a target at a high angle of fire.


One thing to remember is that a tennis ball is a very poor projectile. As a fuzzy sphere it has a relatively high drag coefficient:

Image

Also, since it's mostly air, it has very low density, along with the above means that it loses velocity fairly quickly. It is also very susceptible to environmental effects.

If you want to hit a target at high angles, you definitely need to be taking the wind into account, and mount the cannon in a way that allows precises angles of traverse and elevation to be measured and fixed.
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Unread postAuthor: Technician1002 » Wed May 22, 2013 1:17 am

When done right you can bounce a golf ball off the rim of a wheelbarrow.

Precise power control is essential for this.

[youtube]http://www.youtube.com/watch?v=g496mBQox7Y[/youtube]
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