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my new piston/gun design (ADDED: pics of my toolie piston)

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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my new piston/gun design (ADDED: pics of my toolie piston)

Unread postAuthor: glass_05 » Tue Jun 16, 2009 12:27 am

i know co-axial guns are easiest to build, but i like the looks of an over-under. so i wanted to make a co-axial using a 2inch pipe, and then put two elbows on it going to a 2.5 inch for a tennis ball barrel. what do you think?

i had a test fire last year and it worked well, until my rubber sealing face shot off. i have since fixed that, but before putting it all back together i thought i would ask for some opinions of my design

Image
A) Air is filled into the chamber. As air enters the chambers it pushes the piston forward sealing the barrel inside the chamber.
B) Air is completely filled into the chamber. The same pressure is behind and in front of the piston. The sealing face of the piston remains on the inner barrel.
C) The air behind the piston is released. This causes the air to push the piston back, exposing the hole of the inner barrel. Air from chamber goes into inner barrel, around the elbows. Good bye tennis ball.
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Last edited by glass_05 on Wed Jun 17, 2009 1:06 am, edited 2 times in total.
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Unread postAuthor: Gaderelguitarist » Tue Jun 16, 2009 12:51 am

You'll be getting a severe drop in efficiency due to the ridiculous dead space unless you put your ammo right next to the piston.

Your range and power will be cut drastically because the compressed air will expand in the space between the valve and the round. When this space for compression is small, the gun is efficient, and when it is large, you get the idea.

Edit: I suggest making a Tee valve because then you'll remove the dead space as well as have an over under construction. You'll find they are actually fairly simple in concept and construction.
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Unread postAuthor: glass_05 » Tue Jun 16, 2009 1:20 am

okay. how about this design?
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Re: my new piston/gun design

Unread postAuthor: Technician1002 » Tue Jun 16, 2009 1:52 am

glass_05 wrote:i know co-axial guns are easiest to build, but i like the looks of an over-under. so i wanted to make a co-axial using a 2inch pipe, and then put two elbows on it going to a 2.5 inch for a tennis ball barrel. what do you think?

i had a test fire last year and it worked well, until my rubber sealing face shot off. i have since fixed that, but before putting it all back together i thought i would ask for some opinions of my design

Image
A) Air is filled into the chamber. As air enters the chambers it pushes the piston forward sealing the barrel inside the chamber.
B) Air is completely filled into the chamber. The same pressure is behind and in front of the piston. The sealing face of the piston remains on the inner barrel.
C) The air behind the piston is released. This causes the air to push the piston back, exposing the hole of the inner barrel. Air from chamber goes into inner barrel, around the elbows. Good bye tennis ball.


Without the over/under tennis ball barrel the original is identical to my Mouse Musket a 2 inch chamber 1 inch barrel coaxial. The problem is the volume in the chamber is quite small as the OD of the 1 inch PVC isn't much smaller than the ID of the 2 inch PVC chamber. In relation the tennis ball barrel is quite large. Moving the valve to the other end is exactly what I did in putting a tennis ball barrel on the marshmallow cannon. I left it inline to reduce the dead space and not have the trigger next to the muzzle.

To deal with the volume issue, I went with a larger diameter tank and used a disposable propane tank.

Photo is in this thread. http://www.spudfiles.com/forums/failed-attempt-at-a-silent-tb-launcher-t17989.html

With a 1 inch valve and 36 inch long tennis ball barrel, it launches tennis balls about 300 feet at 100 PSI.
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Unread postAuthor: grock » Tue Jun 16, 2009 2:10 am

the new one would work better, but the U turn is still a bunch of dead space.
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Unread postAuthor: psycix » Tue Jun 16, 2009 5:44 am

The second design is certainly better. I believe it is know as a toolie style piston valve.
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Unread postAuthor: inonickname » Tue Jun 16, 2009 6:27 am

I highly suggest a toolies valve. Have a look on the wiki. You nearly nailed it on the second one.
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Unread postAuthor: glass_05 » Tue Jun 16, 2009 12:06 pm

i will do the toolie piston than. thanks for all your help! i am going to start building it today. i have all he parts, just didnt know how to put it together. pics will come tonight!

thanks again for all the help
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Unread postAuthor: glass_05 » Tue Jun 16, 2009 3:54 pm

got part of the piston done. i am really happy with it so far. UPS guy comes in 1.5 hrs with the rest of my parts
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Unread postAuthor: Technician1002 » Tue Jun 16, 2009 7:10 pm

For and over under design, a piston valve built inside a T works well right on the end of the barrel. Use an elbow the size of the chamber between the chamber to the valve to keep loss to turbulence and restriction to a minimum. An example valve is this one;
http://www.spudfiles.com/forums/slayer-valve-barrel-sealing-piston-all-housed-in-2-te-t9423,vote,viewresult.html
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Unread postAuthor: Gaderelguitarist » Tue Jun 16, 2009 9:14 pm

A toolies valve is definitely an improvement on the original. Though you'll still have more dead space than if you were to use a Tee piston valve.

I'm waiting for those pictures.
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Unread postAuthor: Technician1002 » Tue Jun 16, 2009 9:23 pm

Gaderelguitarist wrote:A toolies valve is definitely an improvement on the original. Though you'll still have more dead space than if you were to use a Tee piston valve.

I'm waiting for those pictures.


Toolies can have a moving mass disadvantage as a long shaft contributes much to the mass, but adds not performance gain other than physical separation of the front and rear piston halfs. The longer a chamber is, the greater this mass is.

For example, the toolie will have a greater moving mass than either of the pistons shown on this page;
http://www.spudfiles.com/forums/project ... rt,60.html

The toolie has an advantage of a large valve seat necking down to a smaller barrel (most of the time). The same effect can be had by using a large valve on a smaller barrel, for example using the 3/4 inch barrel on 1 inch valve.
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Last edited by Technician1002 on Wed Jun 17, 2009 5:37 am, edited 1 time in total.
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Unread postAuthor: Gaderelguitarist » Tue Jun 16, 2009 9:26 pm

This is true.

But which is the lesser of two evils; massive dead space, or a heavier piston.
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Unread postAuthor: glass_05 » Tue Jun 16, 2009 10:12 pm

Gaderelguitarist wrote:I'm waiting for those pictures.

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will finish putting it together tomorrow morning
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Unread postAuthor: Technician1002 » Tue Jun 16, 2009 10:21 pm

@ Glass_05 Nice photos. Is there a possibility the stopper will get stuck?

Gaderelguitarist wrote:This is true.

But which is the lesser of two evils; massive dead space, or a heavier piston.


A piston in a T at the breech of the barrel would be low dead space and still be over/under design.

Edit; removed reference to QDV as requested.
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