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I build my first cannon last weekend, and I'm pretty happy with its performance, I was just anything I did that could be pretty easily improved upon for this cannon, or anything I could do better this time.
The barrel is 3' of 2.5" PVC (for firing tennis balls)
The chamber is 1' of 4" PVC with a shrader valve, pressure meter, and 125 PSI blow off valve tapped in.
The valve is a 1" sprinkler valve with a blow gun tapped in as the pilot valve.
I have two main concerns:
1) The barrel has greater volume than the chamber. I'm pretty sure that this is a problem, but I don't know if I should shorten the barrel, or lengthen the chamber. Because I pump the cannon by hand, I don't want to make the chamber too much bigger than it currently is.
2) I don't know what kind of pressure the tapped in fittings can handle. So far I have been taking it to 100PSI, do you think that is safe? Is there some sort of glue I should put on them to make it more safe?
Any other comments/ tips are more than welcome!
Well, it looks like all your fittings are pressure rated. Good start.
Good valve also. Modded sprinklers can have good power, but with your barrel size, I think a larger porting valve would be way better. Maybe a 1.5" porting piston valve. I know you won't upgrade, just saying it would be better.
Barrel is only 3 feet, could be longer (5 or 6 feet).
Chamber should be bigger. Twice the size I'd say.
You tapped into a single layer. That is a big no-no. You should always use two layers.
You pretty much made the same mistakes most people make on their first. More research could have prevented this, but it is fine. At 100 psi, it is a little dangerous. I say keep it 80 and under (despite the bad performance).
Overall, it is not bad for a first. Slap a smaller barrel on and shoot some golf balls or something for fun. Maybe even smaller for better FPS.
Good for a first, but that end cap cannot be pressure rated. Pressure rated end caps are domed, your rarely see flat surfaces on pressure tanks. a 1.5" SV would be a great power increaser, and I know a place where you could get one for cheap if you PM me about it.
I love lamp
What do you mean by that? Should I have tapped them in where the cap went over the pipe?
Is that the only reason I should keep it below 100PSI? I would be willing to replace the chamber with a 2x as big one to increase performance and so that I could tap in the fittings safely.
Would you mind linking me to instructions on how to build such a valve? I'm still trying to find my way around the site, and It's a bit overwhelming.
Yup, that's right. Though like said above, your end cap is not rated for pressure and should be replaced. Read this article:
http://www.spudfiles.com/spud_wiki/inde ... sure_rated
I would increase the barrel length before increasing the chamber. Your valve is restricting flow a lot, like mentioned above, a larger valve would help. Read this topic to learn about piston valves, though you are still starting out so you may want to pace yourself. Piston valves can be quite difficult the first time you make them.
Oh, wow, I didn't realize that the cap was not pressure rated, thanks!
I guess I need to build a new chamber...
When I do, should I go ahead and make it larger? Is it not really necessary because of the flow of the valve?
With volume constant, is a longer, lower diameter chamber or shorter, higher diameter chamber better? Or does that not really make a difference?
When I make a pneumatic, I try to go for at least a 1:1 ratio (that is, the chamber volume and barrel volume are the same). This really isn't a set-in-stone rule, but it seems to work out.
As far as the chamber goes, I've not really noticed a difference either way. It does matter in a combustion, but the air flow through a pneumatic is a bit different. I'd say go with what you are comfortable with. If you keep it an inline version, it may be better suited to go with a short, fat chamber rather than a thin, long one (for comfort reasons).
As far as the valve goes, even though I am a fan of the sprinkler valve (you can check out the document I made in the Hubb Library, which is recommended), everyone is right. Sprinkler valves are excellent starter valves, but piston valves have much performance increase. I suggest learning as much as you can about the sprinkler valve before starting a piston valve. That way, when you do upgrade to a piston, you will already know a lot of the basics.
I do believe you will find this community rather friendly, and there is lot to be learned from here. Check out the SpudWiki and the search (advanced; not quick search). And welcome to Spudfiles.
When hand pumping a chamber doubling the chamber size does mean twice the effort to pump it up. There is a major advantage to a small chamber when hand pumping a cannon.
A 4 inch diameter chamber 1 foot long is much larger than my Marshmallow cannon which is less then 4 inch by about 7 inch. It does just fine with a 3 foot long tennis ball barrel.
My chamber will fit inside a 4 inch ABS barrel.
I was even able to get decent hang times with tennis balls with a 7 foot long tennis ball barrel. It is true it would fail to launch at lower pressure as there was not enough expansion to eject the ball.
For a hand pumped tennis ball launcher, a 1 foot long 4 inch chamber is fine. Larger is too much work to be fun anymore.
The largest cannon that is worth hand pumping is my ABS cannon. The larger steel tank cannon is too much of a workout to get decent pressure.
If you could possibly get a 1.5 inch sprinkler valve the improved flow will be worth the effort.
Sweet size for hand pumped tennis ball launcher.
That's not fair, Tech. You're using a QDV and not a sprinkler valve.
A 1.5 inch sprinkler valve should closely match a 1 inch QDV.. It is why I recommended it.
Wow, thanks for all the help!
Is a 1.5" sprinkler valve something I might find at Home Depot, or is it a harder to find item?
Also, for future reference, next time I make a post like this, should it go in this topic, or is the cannon showcase page more appropriate?
They aren't normally availible at Home Depot. Most of the time you find them online or you get lucky and find them in a store.
Only by around 17%, which is acceptable for the pressures you're using, going with a longer barrel will give you better performance and a quieter shot for no extra pumping effort.
As to upgrading your valve, why not go straight for a 2"? Not too expensive and it will give you 178% the flow of a 1.5"
I'm thinking I'll just make do with the current valve until I have done enough research to feel comfortable building my own piston valve.
For when I build the CAKE II (It will be the same as the CAKE I except without those dangerous design errors ) If I keep the same valve, what length of 1.5" pipe would be a good barrel for launching golf balls? 7 ft gives me a ~ 1:1 ratio, would that be a good length?
Any clue what kind of range I would get out of that?
Shhhh.. I wanted him to match my little launcher, not beat it..
With your current valve and a golf ball barrel, you can model it in GGDT. Some of the common sprinkler valves are listed on the GGDT site with the valve values to plug in.
Look here for the data.
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