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First Design, T-shirt Cannon, feedback on my initial design.

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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Unread postAuthor: garybdavis » Mon Nov 05, 2012 5:32 pm

Okay, ordered some parts and planning on the "cobble together, test, change some things, test again, repeat..." method. That seems to be the most fun way.

From my further research, the slider valve is actually a three port/two position device as it allows flow in one position and stops the flow + exhaust one side in the other. I thought it was a simple ball valve type operation (2 position/2 port). If so, it won't function in my design like I wanted it to so I'm replacing it with a ball valve. Is my description correct?

Thanks
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Unread postAuthor: MrCrowley » Mon Nov 05, 2012 5:41 pm

Yeah, your assessment is correct but it will be handy if you want a sort of semi-auto capability (with manual reloading). If you use a ball valve, you will either need a second ball valve (or other pilot valve) to exhaust the air behind the valve or you will have to disconnect your air source from the ball valve.

The slide valve simply allows you to have a single pilot valve that controls filling and piloting. If you want to stick with a ball valve, either add a second one to act as the pilot valve or have the air source disconnected before each firing.

I see, though, that you want the ability to change pressure each shot without adjusting the regulator. In that case, a slide valve isn't much help and a ball valve would give better control over the pressure.
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Unread postAuthor: garybdavis » Tue Nov 06, 2012 10:15 am

Here is the rough drawing (Thanks jrrdw for getting it fixed). Additional thoughts are:

2.5" EMT for the barrel
In-line style push button valve instead of a ball valve (looking, but haven't found one yet)
Regulator will be set for 300psi
Pop-off valve for 500psi is $100 - ouch
Has anyone used this type of an in-line blow gun for a trigger and can tell me how well it works?

I orded the QEV, Palmer Female Stabilizer (0-700 output, 3k input, pipe fitting style) and some other parts to start testing. I'm planning on fabing up the pressure chamber with steel pipe and when it shoots good, I'll weld up the ends with plate plugs to have it look a little less "plumbing" style.
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In-Line Blow Gun.jpg
Anyone know how well this would work to pilot the QEV?

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Unread postAuthor: POLAND_SPUD » Tue Nov 06, 2012 10:29 am

Anyone know how well this would work to pilot the QEV?
not as straightforward as a 3 way valve

ohh and seriously there should be only one thing connected to the pilot side of a qev -> a 3 way valve

keep pilot volume as small as possible
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Unread postAuthor: garybdavis » Tue Nov 06, 2012 10:36 am

Are you referring to using a slide valve as the pilot?
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Unread postAuthor: POLAND_SPUD » Tue Nov 06, 2012 10:41 am

yeah a slide valve is a 3 way valve but there are poppet and spool valves too

here some of them look like this one >>>
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Unread postAuthor: garybdavis » Tue Nov 06, 2012 11:03 am

This might work well as the fill valve for the pressure chamber. I'm guessing it's too small for the QEV pilot. At 1/8 NPT, it will mate right up to the PFS. It's even rated at 300psi.

One thing I like about having separate trigger and fill valves is it's less confusing to the novice user. The fill valve is far away from the trigger and ergonomically, you can make the launcher so the user is less likely to push the wrong button to fire.
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Puss-Button Valve, 1/8NPT, 300PSI
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Unread postAuthor: POLAND_SPUD » Tue Nov 06, 2012 11:33 am

uhmm the idea is that it only fires if you press the button... for extra safety add a spingloaded check valve between air reservoir and 3 way valve and you've got an ideal system
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Unread postAuthor: garybdavis » Tue Nov 06, 2012 1:22 pm

Care to spoon feed me a type/source two button, three way valve? :D I can handle the check valve myself. :)
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Unread postAuthor: jrrdw » Tue Nov 06, 2012 1:49 pm

garybdavis wrote:Here is the rough drawing (Thanks jrrdw for getting it fixed).


I'd like to take the credit but it goes to PCGUY. We owe the existence and well being of Spudfiles to him. Thanks PCGUY! :D
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 06, 2012 4:32 pm

garybdavis wrote:One thing I like about having separate trigger and fill valves is it's less confusing to the novice user. The fill valve is far away from the trigger and ergonomically, you can make the launcher so the user is less likely to push the wrong button to fire.


A spring loaded slide valve would be very simple to use - pull the valve and it fires, release it and it fills!

[youtube]http://www.youtube.com/watch?v=YwiHi2oeABA[/youtube]
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Unread postAuthor: garybdavis » Tue Nov 06, 2012 10:56 pm

I'd like to use a slide valve, but I also want to be able to adjust the amount of air I put into the pressure chamber before each shot. (Low pressure for the short range shots - higher pressure for the cheap seats) If it weren't for that, I'd already have one on order.

BTW, after I watched that video for a few times when I found it the other day, I realized that slide valves function as 2-position 3-way. So, thanks for posting it.
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Unread postAuthor: Lockednloaded » Tue Nov 06, 2012 11:31 pm

I hate to parrot, but you really need to reconsider using a slide valve here. I know you want your pressure to be adjustable on the fly, but you can easily achieve that with the palmers reg and a slide valve. A slide valve has to be manually pushed forward in order to fill the chamber, so in order to change pressure on each shot, attach a knob to you palmers reg (to make pressure adjustment easier) and dial in your desired pressure before sliding the valve forward, filling the gun.

I hope you can understand what I'm trying to say here, if not I could draw something up or provide further details to help
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Unread postAuthor: MrCrowley » Tue Nov 06, 2012 11:34 pm

Another way to be able to quickly adjust between pressure ranges would be to have two regulators. One set at the high range and another at the low range. If you put a ball valve between each reg and the air source, with both reg outputs going to a single slide valve, you could choose which pressure range by opening the ball valve before one of the regulators.

LnL, I would have suggested the same but I think he wants to be able to adjust the pressure almost instantaneously. I don't have a Palmer reg so can't comment on how fast you could adjust from, say, 400PSI to 200PSI. I know some of the low pressure regs I have at home take for ever to adjust by turning the knob.

edit: it'd be expensive to have two Palmer regs so depending on the pressure range, you could just use one and then two low pressure regs. It's a lot of added equipment just so you can make quick adjustments but maybe it's what you're looking for.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 06, 2012 11:42 pm

garybdavis wrote:I'd like to use a slide valve, but I also want to be able to adjust the amount of air I put into the pressure chamber before each shot. (Low pressure for the short range shots - higher pressure for the cheap seats) If it weren't for that, I'd already have one on order.


Simply put a ball valve between the slide valve and the main tank - if you plan on adjusting pressure for the subsequent shot, keep this valve closed, voila.

Alternatively, don't put a spring return on the slide valve, it won't refill until you push it forward again.

I'm all for making it accessible to the lowest denominator, but if one is too dim to make out a simple mechanism, maybe you shouldn't be handing them a potentially dangerous pneumatic device...
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