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My New Valve Design

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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My New Valve Design

Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 4:44 am

My new valve design. I just spent about an hour writing all the stuff that tells people about my design, then I accidentally clicked back on the internet explorer and, hey presto! it was gone. So if I can be stuffed in the future, I'll tell yous all about it. So ask away.
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Attachments
1.jpeg
Image of cylinder with bad rendering.
2.jpeg
Image of whole valve (minus actuating cylinder which attaches onto disc on the left).
3.jpeg
Better rendering showing the whole valve. Note: the lighter circle in the front is a piston inside the cylinder.
4.jpeg
Image with piston in contrast.
5.jpeg
Image showing the front of the valve. Note: the disc at the front (piston backstop) only has 8 holes, I found out it needed 12 so I have changed it.
6.jpeg
Image showing valve in closed position.
7.jpeg
Image showing valve half open (view through port hole showing the lighter coloured piston closing the port hole halfway and expanded part of piston with neoprene gasket material for shock absorbing almost hitting the backstop).
8.JPG
Image of valve with labels.
9.jpeg
Image showing valve fully open as neoprene absorbs shock from impact of the expanded part of piston hitting backstop. Note: the relatively thin cylinder on the right is the actuating piston that goes in the actuating cylinder (not shown).
11.jpeg
Another image showing valve in open position from a different perspective.
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Unread postAuthor: Technician1002 » Wed Jul 08, 2009 4:56 am

From the size of the ports in relation to the piston, am I correct in assuming this is a chamber sealing piston with many small ports instead of fewer large ones so it can handle high pressure? It looks overly complicated contributing to a relatively low COF. A single port with a cross section is higher effeciency than 4 ports with a total cross section of the single port.

Is there a reason for 12 ports when 3 with the same cross section area would do the job?

One of my early air cannons used a ring of round ports for the valve. Performance was poor. I still have it if you would like photos.
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Unread postAuthor: inonickname » Wed Jul 08, 2009 4:57 am

Very nice renderings and all!

It looks like a good design, from what I gather it's an efficient positively acting piston valve?
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 5:21 am

Technician: Yes, I'd like to see those images please. If I used bigger holes around the outside the holes on the outside would allow more air through than the center port hole, unless the overall diameter of the valve (80mm) is compromised. What I mean is that I found a good ratio for this design. The center port hole is 42mm diameter and the 12 holes are 12mm, surface area of the center port hole and surface area of the combined 12 port holes are pretty much the same, you can do the math. I worked out the 42mm hole provides a surface area of ~1385mm squared and the 12 holes provide ~ 1357mm squared surface area. In theory, bigger scales could be used and the efficiency would be maintained. Having said, however, the efficiency could be improved, as miniscule a matter it is. I merely used the dimensions regarding accessibility to tools such as drills. In other words use of fewer, larger holes on the outside will decrease the center port hole, unless the valves overall diameter is compromised. P.S Yes I suppose it is a chamber sealing piston.
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Last edited by .:: :TomDom: ::. on Wed Jul 08, 2009 5:37 am, edited 1 time in total.
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 5:25 am

inonickname: I'm not sure what I'd call it, I know it's some kind of piston valve, but that sounds good, not that I truly know what it means... maybe you could tell me? :idea: the term "positively acting" has me stumped. lol :D P.S Thanks for the complimant and comments so far Technician1002 and inonickname
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Unread postAuthor: inonickname » Wed Jul 08, 2009 5:34 am

Well, most spudgunning pistons are "negatively acting" - this means that the pilot volume is removed to fire the gun. Less commonly, there are "positively acting" pistons which add pilot volume to fire, such as Solar's eclipse.

So does this add or remove pilot volume to fire?
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 5:47 am

inonickname: As I said, I haven't been on this site for some time now, I'm not too familiar with anything atm (Solar's eclipse), but thanks for the info. I'm kinda confused with "pilot volume" I'm assuming it's the pressure in, say, a modified sprinkler valve that holds the diaphragm down. If so, then this is a common negativlely acting piston valve. The pilot volume would be applied to the smaller, thinner piston I call the actuating piston. The actuating piston would run inside the actuating cylinder which isn't shown. On the labelled diagram I've labelled where it would go. Once the pilot volume is removed the larger, main piston would come forward and open the ports.
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Unread postAuthor: Technician1002 » Wed Jul 08, 2009 6:07 am

I worked out the 42mm hole provides a surface area of ~1385mm squared and the 12 holes provide ~ 1357mm squared surface area.


This uniform area is a common thought in spudding. In fluids, this works out to uniform velocity. The assumption is made the surface area drag is also the same.

In gasses, as the pressure drops through the valve, using gas laws, the gas expands. It has larger volume. A uniform cross sectional pipe, valve assy will choke it's own flow by not allowing for the expansion.

The long uniform diameter pipe is exactly how a capillary expansion valve works in a refrigerator. Instead of using a small orifice to meter freon from the high pressure liquid side to the low pressure side, a much larger cross section tube is used that due to the size is much less likely to plug. With a long length, it has the same flow restriction of a much smaller orifice. Your long same cross section path has the same restriction to flow.

Time to do the math. Find the circumference of a single 1385mm squared hole and the circumference of the same cross section area tucked into 12 smaller holes. The 12 smaller holes have a lot more drag.

It's easier to visualize in your head if you think of all the holes as a honeycomb. A dozen holes. Lots of surface area total. Remove the honeycomb and leave the same area as a single hole. Mmm, less surface area, less drag. What used to go through against a wall in the center of the cluster of honeycomb tubes now has no walls and is surrounded by air moving the same direction.. for no friction. Only the outside edge rubs on a wall. Less drag. Big ports, same total area = higher flow efficiency.

With this in mind it is a good idea to design all the plumbing to be as low restriction as possible. If a component is a restriction, such as a valve orifice, good practice is to port larger on both sides of the restriction and not extend the length of the restriction any more than possible.

Having ports designed to be the exact same cross section of a valve seat is common in designing piston valves. An example is designing pistons to open no more than 1/4 diameter. Unfortunately it extends the length of the restriction or makes a second series restriction that could easily be reduced or eliminated.

Without seeing the cannon this valve assy is installed inside, I can't recommend ways to improve it without compromising the overall diameter. Even taking the 4 sets of groups of 3 ports and turning them into oval single ports would both increase the cross sectional area while reducing the total circumference area. Instead of the 12 ports, 4 oval ports could replace them for higher efficiency.


Oh, and reference material for additional reading is here on selecting a capillary tube size for refrigeration.
http://findarticles.com/p/articles/mi_m5PRC/is_2_112/ai_n24998225/
http://www.coolit.co.za/captube/index.htm

Table with sizes and length for various refrigeration applications;
http://www.rparts.com/Catalog/Major_Components/valves/Cap_Tubing_Sizing%20Table.htm

Small refrigerators use capillary tubes instead of small orifices which tend to plug up because they are much smaller.

On the pictures, I'll have to take some later.
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 6:20 am

Technician: Well... I see where you get your name from lol. About half the stuff you said I understood, I got the bit about drag from all the holes. I never thought of using oval holes, but they would prove to be most beneficial, although unpractical. Overall I think this design is still going to be made, unless I can find a way to make oval holes. I'm just a student at school though, at almost 18 I still haven't got anything to make this, except for stuff at school or a workshop. One day though... one day.
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 6:35 am

I designed this valve to fit into a pipe, so to be discrete. I'm also pretty confident when I say that if this design is used with a 1" barrel, the air flowing, pushing the projectile out of the barrel will have no restrictions. The flow rate of the air coming out of the valve would probably be no less than the flow rate of a 1" pipe, but, considering what you've said I suppose opting for a flow rate that a 42mm pipe would provide is something I cannot ask of this design. So... if someone made this valve and put the output on a flow meter I'm sure that the flow rate could be found and the valve could be used for barrel sizes in the range of whatever flow rate would like to be achieved. If the valve needs to let more air through, the design could be upscaled. P.S Thanks for the effort for the pictures, I would like to see them, but, if it's too much of a hassle you needn't worry, I thought you had them on file or something.
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Unread postAuthor: .:: :TomDom: ::. » Wed Jul 08, 2009 6:47 am

Overall, I think this design would be almost simple to make a valve from and the valve would perform good in a pneumatic gun. The design is also handy as it can be upscaled or downscaled easily for use in larger or smaller cannons.
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Unread postAuthor: Hubb » Wed Jul 08, 2009 8:29 am

Whoah, slow down on the simultaneous posting a bit.
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Unread postAuthor: Moonbogg » Wed Jul 08, 2009 10:19 am

It looks cool. I have no idea how it works though. I'd have to see the rest of the gun or at least how it installs.
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Unread postAuthor: mobile chernobyl » Wed Jul 08, 2009 8:10 pm

Cool a super complicated spool valve lol. That looks like it will be fun to make... It actually looks like an inversion of tech's QDV, which is an inversion of unbalanced spool valves the paintball world over.
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Introducting the Light Saber

Unread postAuthor: Technician1002 » Wed Jul 08, 2009 10:10 pm

.:: :TomDom: ::. wrote: P.S Thanks for the effort for the pictures, I would like to see them, but, if it's too much of a hassle you needn't worry, I thought you had them on file or something.


Photos are in of one of my antiques. I don't remember what year i built this. It's over 18 years old. I built it before I got married. So those new folks who think of giving up when a first design doesn't work as planned... don't give up.

This was built before Spudfiles existed. I was on my own. Many of the things I learned, were used in the Mouse Musket. This is a 2 inch chamber 1 inch barrel coaxial. This was my first attempt at a narrow ratio piston.

Worried that the o ring would get stuck in ports, the ports are a ring of 1/4 inch holes at the breech of the barrel next to the reducer that seals the chamber from the pilot

The piston extends into the barrel with an o ring that passes the ports sealing the barrel. To seal off the chamber, a reducer is inside the coupling. The breech of the barrel is quite long past the ports, so the piston is long and thus heavy. The combination of the long piston and small ports made this a pretty wimpy launcher, when I got it to fire. It didn't use floating rings. Graphite lube was used to reduce friction.. it leaked like a sieve. To make matters worse, it needed a hefty spring to close it, which didn't help it open.

Without further adeu, the Ligtht Saber (Star Wars era) decorated with reflective barrier tape.
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Attachments
Overview.jpg
Overall view of the Light Saber. Covered in reflective tape. At night easy to spot in the dark in headlights or a flashlight beam.
Overview.jpg (27.98 KiB) Viewed 1317 times
Light Saber.jpg
Light saber glowing in the camera flash. Awesome at night.
Light Saber.jpg (23.92 KiB) Viewed 1317 times
SaberBreech.JPG
Close up of the breech. Blowgun trigger is removed.
Saber Valve.JPG
Light saber valve parts. Small bumper, big spring and huge heavy piston. An early design that didn't break PVC pistons. Way too slow to do that.
Saber Valve1.JPG
A really dark peek into the breech. Graphite grease didn't help by making everything black. Lightened it up some in the Gimp. Reducer, piston cylinder, barrel breech, and ring of small ports in the barrel can be seen.
Saber Valve1.JPG (39.02 KiB) Viewed 1317 times
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