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Help with my valve/design choice

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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Help with my valve/design choice

Unread postAuthor: Andy_ » Mon Apr 29, 2013 5:32 pm

Hello,

Unimportant info
My old combustion cannon has died so I've been looking to build a new one, I came here to this site and this is the first time I discovered pneumatic cannons, so I've been reading about them for a while and now I understand how they work and various types of valve etc
I have finally decided on a design that I would like to build but I wanted to ask first

Important info
I want to replicate this mans gun

[youtube]http://www.youtube.com/watch?v=eBdqCI7-np8[/youtube]
He uses a piston valve and a spring loaded hammer to open the piston for a quick burst of air from the chamber. This seems like you could get some decent pressure out if you had a big enough piston valve. (I'm still wondering how he welded the alu can to the brass fitting)

But, I was also thinking of using a QEV with a blow gun at the exhaust. I believe this would dump the entire canister when triggered. Which makes me think it would deliver more power than the piston/hammer combo. But it would only be single shot use

Real question
What would deliver more power, a piston and hammer valve combo like in the video, or a QEV with a blow gun as the trigger?
And would a larger calibre of ammo (example: marble VS BB) travel faster?

Thanks for your time,
Andy
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Unread postAuthor: RBurke83 » Mon Apr 29, 2013 8:09 pm

There are much more powerful designs that use the same or less fittings than that gun. Maybe he's a member here, but that thing looks like an accident waiting to happen. I wouldn't trust that spray can chamber with 80 psi. You should consider a copper coaxial pneumatic to start playing with air in.

Edit: to answer your real question, which I just noticed, can't say for sure as we can't see his internals. Well, I didn't bother sitting through 9 minutes of the whip cream can gun so maybe he did take it apart. Anyway, can't go wrong with a store bought purpose built valve. And they can even be modded to shoot full auto. A lighter projectile will have a higher initial velocity, while a more massive projectile will retain its velocity longer. You can't really compare projectiles of diff sizes and weights, at least not practically.
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Unread postAuthor: Andy_ » Mon Apr 29, 2013 8:23 pm

RBurke83 wrote:There are much more powerful designs that use the same or less fittings than that gun. Maybe he's a member here, but that thing looks like an accident waiting to happen. I wouldn't trust that spray can chamber with 80 psi. You should consider a copper coaxial pneumatic to start playing with air in.

Edit: to answer your real question, which I just noticed, can't say for sure as we can't see his internals. Well, I didn't bother sitting through 9 minutes of the whip cream can gun so maybe he did take it apart. Anyway, can't go wrong with a store bought purpose built valve. And they can even be modded to shoot full auto


What sort of store bought valve? Like a store bought QEV with a blowgun?

Also what is 'coaxial' and how does that work? Is that like using a copper pipe as your chamber?
I would have thought that a canister like that would be fine since it's main job is to hold pressurized gas/liquid

Thanks for your input
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Unread postAuthor: RBurke83 » Mon Apr 29, 2013 8:32 pm

A coaxial as a gun in which the camber and the barrel both share the same axis. You have your barrel down the center of a larger chamber. This eliminates the use of much of the plumbing which makes up a typical pnuematic.

http://nighthawkinlight.wonderhowto.com ... e-0141605/

That design, made in copper would be capable of 400psi, given quality workmanship, and construction technique[/img]
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Unread postAuthor: Andy_ » Mon Apr 29, 2013 9:15 pm

RBurke83 wrote:A coaxial as a gun in which the camber and the barrel both share the same axis. You have your barrel down the center of a larger chamber. This eliminates the use of much of the plumbing which makes up a typical pnuematic.

http://nighthawkinlight.wonderhowto.com ... e-0141605/

That design, made in copper would be capable of 400psi, given quality workmanship, and construction technique[/img]


So you could basically copy this design, except with copper, and instead of a ball valve you could have a blow gun?

The copper pipes I can get from my local hardware store are

Pipe 1) 10.88mm ID / 12.70mm OD
Pipe 2) 17.01mm ID / 19.05mm OD

Assuming I used 1000mm length then..

Pipe 1) 126ML external volume
Pipe 2) 227ML internal volume

Total 100ML of chamber volume

or for the americans
0.0266 Gallons of chamber volume

Would this be sufficient chamber volume?



edit:
The internal volume of the barrel would be 92ML (0.0246 gallons)
Does that mean the barrel to chamber ratio would be 1:1.086?? Not sure how barrel ratio works or how it effects projectile

double edit:
How do you breach load with a coaxial?
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Unread postAuthor: Gippeto » Mon Apr 29, 2013 11:14 pm

Sort through a couple more of his videos. Not what we'd call a piston valve....I'd call it a poppet valve...or hammer valve.

This is in the how to section;

http://www.spudfiles.com/forums/hammer- ... 23202.html



As to your question though:


What would deliver more power, a piston and hammer valve combo like in the video, or a QEV with a blow gun as the trigger?


Of course, he doesn't have a piston valve. IF he had a piston valve and hammer valve pilot...I would certainly favor that as being the winner for flat out power.

Chamber sealing piston valve with a hammer valve pilot would be interesting...would get multiple shots per fill. 8)
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 30, 2013 12:08 am

Instead of a blowgun, use a three way valve as a pilot.

A slide valve is one option: http://www.spudfiles.com/forums/semi-au ... 23626.html

There are many more valves though that would fit the bill in different configurations, for example:

http://www.ebay.com/itm/1-8-PT-Female-T ... 484fbd5fbb

Gippeto wrote:Chamber sealing piston valve with a hammer valve pilot would be interesting...would get multiple shots per fill. 8)


Pretty much what Brian was doing with his repeater: http://www.spudfiles.com/forums/b2tb-sa ... 14817.html
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Unread postAuthor: Andy_ » Tue Apr 30, 2013 6:34 am

hmm good reading, but a few questions

1) JSR, how does this three way valve work? do you mean a QEV?

2) I could try a slide valve, but how would that work better than a blow gun?

3) Does the speed that i move my hand effect how fast the projectile exits when using a slide valve?

4) How do you make a breech loader for a coaxial gun
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 30, 2013 6:47 am

Andy_ wrote:hmm good reading, but a few questions

1) JSR, how does this three way valve work? do you mean a QEV?

2) I could try a slide valve, but how would that work better than a blow gun?


A three way valve is what you would use to pilot the QEV. From another post, here's an explanation of the concept:

Image

When the valve is in the forward position, it allows air to flow from the main supply to the QEV and fill the pilot and firing chamber.

When the valve is in the rear position, two things happen:

- main supply is cut off

- QEV pilot chamber is open to the atmosphere, emptying it and firing the launcher

The valve goes back to the forward position (you need to add a spring or do it manually) and the cycle can be repeated.

This is the concept:

Image

The slide valve is basically a three way valve.

A three way valve has three ports, which we will call A, B and C

There are two possible paths, AB (with C blocked off) and AC (with B blocked off)

A is connected to the pilot area of the QEV

B is connected to your main air supply

C is simply left open to the atmosphere.

The QEV's other ports are connected to a barrel and to a firing chamber, big enough to hold enough air for one shot.

At rest, the three way is in position AB. This means your reservoir is filling the launcher chamber.

When the trigger is pulled, the valve switches to position AC. This means the main air supply is blocked off, and is no longer filling the pilot and chamber, while the pilot is exhausted to the atmosphere, which fires the launcher.

Once the trigger is released, the valve goes back to AB, which reseals the valve, refills the pilot and firing chamber and the cycle can be repeated.

3) Does the speed that i move my hand effect how fast the projectile exits when using a slide valve?


As with all pilot valves, the faster they open, the better performance you will get.

4) How do you make a breech loader for a coaxial gun


Have a look at wyz' excellent tutorial: http://www.spudfiles.com/forums/how-to- ... 24038.html
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Unread postAuthor: Andy_ » Tue Apr 30, 2013 7:37 am

WOW
JSR you are seriously an asset to this forum.
Thankyou for your response
Wyz made that all look so simple!

Do you think you could somehow attach a trigger to the slide valve so you can hold the gun normally and fire it? then maybe you could put a spring behind the trigger to push the slide valve back forwards in place, refilling the chamber and ready for the next shot

One more thing.. what if I don't have a constant air supply like the gun uses? What else could I use? Apparently deodorant canisters are too weak :S
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 30, 2013 8:32 am

Andy_ wrote:WOW
JSR you are seriously an asset to this forum.
Thankyou for your response
Wyz made that all look so simple!


It's a common question, I pretty much copy-pasted a previous response ;)

Do you think you could somehow attach a trigger to the slide valve so you can hold the gun normally and fire it? then maybe you could put a spring behind the trigger to push the slide valve back forwards in place, refilling the chamber and ready for the next shot


Yep, folks have done it. Example: http://www.spudfiles.com/forums/semi-au ... 22363.html

As I said though, there are other types of three way valves that are more "trigger like" such as the one linked to in my first response.

One more thing.. what if I don't have a constant air supply like the gun uses? What else could I use? Apparently deodorant canisters are too weak :S


What pressure do you want to run at and what's your budget?
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Unread postAuthor: RBurke83 » Tue Apr 30, 2013 8:44 am

You will have to purchase a pump which suits the intended pressures. For self contained shooting without pumping, you are entering the territory of PCP commercial airguns. These guns typically have a chamber containing enormous pressures, measured in 1000's of psi's.
A trade off could be a chamber design which has multiple ball valves. Say you have a chamber of 20 mm diameter and 750mm in length. If you placed a ball valve at 250mm and then another at 500mm, you would have three chambers which can be opened and closed for three shots. I shoot darts, and if I were to use this design:

Both ball valves open, full 750 mm chamber is filled to 150 psi. Then first ball valve near the piston would close and I would pressurize the middle and last chamber to 275 psi. Close the final ball valve and pressurize the last 250mm section to 400psi. For shooting, first shot is at 150 psi, first ball valve opens, which closes piston and equalizes with the 1st and 2nd chamber to approx 150 psi again. Same with 3rd chmber and 3rd shot
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Unread postAuthor: Andy_ » Tue Apr 30, 2013 8:53 am

jackssmirkingrevenge wrote:What pressure do you want to run at and what's your budget?


I have no idea of what pressure gives what results. I've only ever used spray and pray combustion cannons.

I want it to be powerful enough to theoretically take down small~medium game. But I won't be using it for this purpose.

I wouldn't want to spend any more than $100
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 30, 2013 9:29 am

Low budgets usually take HPA out of the equation.

Are you set on semi-auto or will a single shot high powered pneumatic do?

Have you had any thoughts as to what calibre and sort of ammunition you would use?
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Unread postAuthor: Brian the brain » Tue Apr 30, 2013 9:55 am

Pretty much what Brian was doing with his repeater: http://www.spudfiles.com/forums/b2tb-sa ... ter-t14817. html


Forgot about this one?:

http://www.spudfiles.com/forums/old-sha ... 17827.html

modifying a QEV ( easy mod) enables it to fire multiple shots from a single chamber.

You'll need less parts:
Chamber, QEV, homemade hammervalve, barrel and... offcourse a filling valve.

The homemade hammervalve consists of a reducer, an O-ring, a small spring and a screw/bolt with a capnut on the end.Also not to difficult to build or hard to come by.

You can then add any type of breechloading method you like.

If you really want to impress I suggest using a blow forward-bolt and a double action trigger.
( pull trigger-hammer builds up tension-hammer releases.Release trigger to reset.)

we can guide you through this process, or provide links.
Que JSR in 3...2....1... :D


The cheapest way of getting high pressure is to build yourself a stirrup pump.
We've got an excellent how-to on those too somewhere.. :roll:
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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