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A couple beginner questions

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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A couple beginner questions

Unread postAuthor: U1timateWaff1e » Sun Jul 17, 2011 5:37 am

Hi all!

So I am pretty new to the forums, and I have recently just got into pneumatic weaponry. My first rifle was a 100psi PVC double ball valve that I used to shoot nails that were wrapped with electrical tape. Previously before this I built a gargantuan 6 foot long combustion potato cannon that used a taser as ignition. But this is not relevant.

I am planning on making a 400-500 psi full metal gun that will use an empty 12oz co2 canister and metal fittings for the tank (and of course a psi gauge and some type of a valve in order to put air into the tank), and use a high pressure solenoid valve as the trigger. The default ammunition that I would use are either 1/4" or 1/2" steel slingshot balls, OR .25" pellets that are normally used in store bought air rifles.

Here are my questions-

1. My budget is not very large, and so buying a very high end, high psi air compressor will not be an option. I have heard of so called "shock bicycle pumps" and how they can get up to ridiculously high pressures for hand pumps, but I do not fully understand what these are. Can somebody explain what they are and where I could possibly buy one? Will this be the best option for this project?

2. What type of valve should I use to get air into my tank? Is there a alternative to a tire schrader valve that I should be using?

3. http://cgi.ebay.com/ebaymotors/ws/eBayI ... 602wt_1165

When I was looking at this it seemed too good to be true. Moderately low price, high pressures, large orifice, high flow, 1/2" connections. Does this solenoid valve look sound to use in this project?



Thanks for all of your help! :D
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Unread postAuthor: Alster370 » Sun Jul 17, 2011 5:59 am

1.) shock pumps are basically small diameter pumps that allow you to fill to higher pressures, but at a slower rate. This is a common shock pump.

http://www.allterraincycles.co.uk/product/8018.html

although even higher pressure models can be found:

http://www.drakescycles.co.uk/m2b66s336 ... _600/RS_GB

2.) I would stick with a shrader for now because its very reliable, cheap and compatible with pretty much everything including shock pumps.

3.) Not really sure but ive seen them used before on guns. Why not a piston valve? much cheaper.
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Unread postAuthor: Crna Legija » Sun Jul 17, 2011 6:05 am

shock pump its just like a normal pump but with a small surface area piston so you can get high pressure. only good for small chambers, under 50ml really.

i would look at getting a fridge compressor, I hit 900psi with my one.

you can use Paintball Quick Disconnect for a fill valve.


that eBay looks fine but a 1/2'' Quick Exhaust Air or bigger and have a much more power full gun. its not rated for 500psi but many of people have used them at 500-700psi.
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Unread postAuthor: daniel0663 » Sun Jul 17, 2011 6:11 am

Welcome !

Sounds like it will be a decent build.

1. No, it wont be the best option to buy a shock pump. Reason being is because of your 12oz co2 tank you have to fill up. You're standard shock pumps only pump out a limited amount of air, and would take you a LONNGGG time and effort to pump the tank up to 400-500psi.
besides, commercial bike shock pumps only have a max pressure rating of 300-400 psi.

I sugest you either lower the chamber volume and use pressures between 300-400psi or you build a homemade high pressure pump which is more suitable for your plan.

2. Alternative valve can be quick dissconects with ball valves.
But if you want to pump it up with a shock pump, you must use a
schrader valve, or a preistzo valve.

3. Why use a expensive solenoid valve? You can make or buy a QEV for half the price.
Even with $20-30 you can buy the materials to make a real decent performing piston valve.

If you want to take the path of a commercial valve, i would suggest you buy a QEV which you can buy for half the price of that solenoid valve and it will perform just as well or even beter.
here is a link to one.


http://cgi.ebay.com/Pneumatic-Quick-Exh ... 3ca1f7c8e2


Good luck !
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Unread postAuthor: daniel0663 » Sun Jul 17, 2011 6:13 am

that eBay looks fine but a 1/2'' Quick Exhaust Air or bigger and have a much more power full gun. its not rated for 500psi but many of people have used them at 500-700psi.


ah! Crna legija bet me to it :P
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Unread postAuthor: Crna Legija » Sun Jul 17, 2011 6:17 am

daniel0663 wrote:
that eBay looks fine but a 1/2'' Quick Exhaust Air or bigger and have a much more power full gun. its not rated for 500psi but many of people have used them at 500-700psi.


ah! Crna legija bet me to it :P


No need to double post about it :lol:
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Unread postAuthor: saefroch » Sun Jul 17, 2011 11:02 am

I personally suggest a homemade small-diameter floor pump (or stirrup pump). They can be built on a relatively low budget and reach very high pressures. The longer stroke length helps compensate for the small displacement caused by the small head diameter. Here's mine if you think you're up for it.

For a fill valve, most standard quick disconnect couplings have a check valve in the female side, so the do not leak after disconnected. That's what I suggest. You can get a 1/4" NPT set for $6 on McMaster.

Solenoid valves are usually not suggested because of the slow opening time.
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Unread postAuthor: Fnord » Sun Jul 17, 2011 1:55 pm

Uh, something else you may want to consider is your chamber-to-barrel ratio. Without looking it up I'm going to guess a 12oz tank has a volume of around 30 cubic inches. Unless you're going with a very looong 1/2" diameter barrel this will mostly be a waste for a single shot.

A chamber about twice the volume of your largest barrel is more than you need with such high pressures.
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Unread postAuthor: U1timateWaff1e » Sun Jul 17, 2011 4:24 pm

Thank you for all the replies!

The reason for me using a large volume tank, and for wanting to use a solenoid valve was that I was planning on messing with semi-auto features.

I realize now that that is not possible now because solenoid valves take a time to actually work.

For instance, I was planning on wiring up a momentary switch connected to the solenoid so that I could tap the button, and a very small amount of air would be released. Then I could put more ammo in the barrel and then tap the switch again.
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Unread postAuthor: Crna Legija » Mon Jul 18, 2011 3:23 am

U1timateWaff1e wrote:Thank you for all the replies!

The reason for me using a large volume tank, and for wanting to use a solenoid valve was that I was planning on messing with semi-auto features.

I realize now that that is not possible now because solenoid valves take a time to actually work.

For instance, I was planning on wiring up a momentary switch connected to the solenoid so that I could tap the button, and a very small amount of air would be released. Then I could put more ammo in the barrel and then tap the switch again.


if you mod the valve and pilot it with a 3way solenoid then you could do that
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Unread postAuthor: U1timateWaff1e » Mon Jul 18, 2011 4:25 am

Crna Legija wrote:
U1timateWaff1e wrote:Thank you for all the replies!

The reason for me using a large volume tank, and for wanting to use a solenoid valve was that I was planning on messing with semi-auto features.

I realize now that that is not possible now because solenoid valves take a time to actually work.

For instance, I was planning on wiring up a momentary switch connected to the solenoid so that I could tap the button, and a very small amount of air would be released. Then I could put more ammo in the barrel and then tap the switch again.


if you mod the valve and pilot it with a 3way solenoid then you could do that


With a solenoid or a quick exhaust valve?
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Unread postAuthor: Crna Legija » Mon Jul 18, 2011 4:40 am

both, but you dont have to mod the qev.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 18, 2011 4:44 am

I think a slide valve would work well in conjunction with a QEV for your purposes, have a read throughthis thread ;)
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Unread postAuthor: U1timateWaff1e » Mon Jul 18, 2011 11:51 pm

Crna Legija wrote:shock pump its just like a normal pump but with a small surface area piston so you can get high pressure. only good for small chambers, under 50ml really.

i would look at getting a fridge compressor, I hit 900psi with my one.

you can use Paintball Quick Disconnect for a fill valve.


that eBay looks fine but a 1/2'' Quick Exhaust Air or bigger and have a much more power full gun. its not rated for 500psi but many of people have used them at 500-700psi.


On the ebay description, it says that it is pressure rated for 140psi. Are you sure that taking it up to 500+ psi is safe?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 19, 2011 12:01 am

U1timateWaff1e wrote:On the ebay description, it says that it is pressure rated for 140psi. Are you sure that taking it up to 500+ psi is safe?


Yes.
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