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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.
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.
Very nice renderings and all!
It looks like a good design, from what I gather it's an efficient positively acting piston valve?
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.
Last edited by .:: :TomDom: ::. on Wed Jul 08, 2009 5:37 am, edited 1 time in total.
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? the term "positively acting" has me stumped. lol P.S Thanks for the complimant and comments so far Technician1002 and inonickname
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?
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.
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.
Table with sizes and length for various refrigeration applications;
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.
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.
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.
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.
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.
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.
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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