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My First Pressure gun ever. Over/Under Design, need help.

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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Unread postAuthor: Yukondano2 » Sun Nov 21, 2010 12:59 pm

Gun Freak wrote:HAHAYYY thats my gun :D
For my brace, I used a block of wood, and a hole saw to cut cirles out of the appropriate size. The I cut the circles off halfway to make semi-circle holes in which the barrel and chamber sit in. A hose clamp or similar can be used to secure it.


I don't know what a hose clamp is nor do i have one so I'll just use Duct tape :D

Also are those 45 degree pieces pressure rated? i might want some of those for my second gun.

Also in that gun, how does the valve work? It isn't blocking the chamber from the barrel. Or is it some sort of piston.
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Unread postAuthor: Gun Freak » Sun Nov 21, 2010 1:06 pm

Yeah the 45's are PR.
It is a 2" housed piston valve with a modified 1" sprinkler valve pilot.
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Unread postAuthor: Yukondano2 » Sun Nov 21, 2010 1:16 pm

Gun Freak wrote:Yeah the 45's are PR.
It is a 2" housed piston valve with a modified 1" sprinkler valve pilot.


I redesigned my gun to have a stock, though the air from the chamber is flowing through it. Does performance go down the more turns?
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Unread postAuthor: mlz3000 » Sun Nov 21, 2010 1:24 pm

Yukondano2 wrote:I redesigned my gun to have a stock, though the air from the chamber is flowing through it. Does performance go down the more turns?


Yes, although if I understand correctly, when the valve opens, air flows from the chamber through the stock to the barrel. The bigger problem here would be the space in between the chamber and the barrel.

If the stock is part of the chamber (i.e. when you said "the air from the chamber is flowing through it" you meant that the stock gets pressurized too), then the bends do reduce performance some, but you're not going to notice it at all, especially with a ball valved gun.

EDIT: And sorry Gun_Freak for not posting the whole thread of your gun. There were many pictures of the workings of the piston, and I figured that just a picture of the outside would get my point across better.
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Last edited by mlz3000 on Sun Nov 21, 2010 1:27 pm, edited 1 time in total.
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Unread postAuthor: Yukondano2 » Sun Nov 21, 2010 1:26 pm

mlz3000 wrote:
Yukondano2 wrote:I redesigned my gun to have a stock, though the air from the chamber is flowing through it. Does performance go down the more turns?


Yes, although if I understand correctly, when the valve opens, air flows from the chamber through the stock to the barrel. The bigger problem here would be the space in between the chamber and the barrel.

If the stock is part of the chamber (i.e. when you said "the air from the chamber is flowing through it" you meant that the stock gets pressurized too), then the bends do reduce performance some, but you're not going to notice it at all, especially with a ball valved gun.


Yeah the pressure is in the stock. I your advice of a straight shot from the valve out the barrel. I want this to perform DECENTLY.
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Unread postAuthor: mlz3000 » Sun Nov 21, 2010 1:33 pm

Might I suggest one of these?

They're $19 (+shipping), already modded, and you'll get worlds of performance over using a ball valve.

Plus you get to fire it with a pull of a trigger, rather than a twist. I always like that better myself :D.

EDIT: I found a canon where the barrel support is very visible here.
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Unread postAuthor: Gun Freak » Sun Nov 21, 2010 4:01 pm

mlz3000 wrote:And sorry Gun_Freak for not posting the whole thread of your gun. There were many pictures of the workings of the piston, and I figured that just a picture of the outside would get my point across better.

Ohhh no no it's cool, I was happy you posted a pic of my gun!
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Unread postAuthor: Yukondano2 » Sun Nov 21, 2010 6:38 pm

mlz3000 wrote:Might I suggest one of these?

They're $19 (+shipping), already modded, and you'll get worlds of performance over using a ball valve.

Plus you get to fire it with a pull of a trigger, rather than a twist. I always like that better myself :D.

EDIT: I found a canon where the barrel support is very visible here.


I was going to use one of those in my second gun. I'm going to use a 1" barrel and a 2" Chamber. This is a 1/2" barrel and 1" chamber. I did it because I learned a 1/2" barrel and 2" chamber wouldn't work very well at ALL. Besides, I don't trust that site. Not a grudge or anything, I just don't know anything about who owns it or anything similar. I can mod it myself anyhow. They have that exact same valve in my local hardware store. Not sure about blowguns though, They didn't know exactly WHAT I was talking about when I went there, so when I begin working on the second one I'm going to bring a picture.
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Unread postAuthor: Technician1002 » Sun Nov 21, 2010 7:13 pm

What is wrong with a 1/2 inch barrel and a 2 inch chamber?

Excess chamber volume is a waste. For a large diameter chamber, it can be much shorter. Double the diameter only needs 1/4 the length for the same volume.

I launch AA batteries through washing machines with a 4 inch chamber and a 1/2 inch barrel.
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Unread postAuthor: Yukondano2 » Sun Nov 21, 2010 7:46 pm

Technician1002 wrote:What is wrong with a 1/2 inch barrel and a 2 inch chamber?

Excess chamber volume is a waste. For a large diameter chamber, it can be much shorter. Double the diameter only needs 1/4 the length for the same volume.

I launch AA batteries through washing machines with a 4 inch chamber and a 1/2 inch barrel.


So it will perfrom the same with a large chamber so long as the chamber is short? Why?
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Unread postAuthor: Technician1002 » Sun Nov 21, 2010 8:23 pm

Same volume. CB ratio remains the same.

Edit;

In some cases, the short fat chamber will outperform a long skinny one due to the resistance to flow. For example a 1/4 inch airhose 50 feet long simply can't deliver the volume needed to launch a spud like a much shorter 2 inch chamber of the same volume.
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Unread postAuthor: Yukondano2 » Mon Nov 22, 2010 6:53 pm

Technician1002 wrote:Same volume. CB ratio remains the same.

Edit;

In some cases, the short fat chamber will outperform a long skinny one due to the resistance to flow. For example a 1/4 inch airhose 50 feet long simply can't deliver the volume needed to launch a spud like a much shorter 2 inch chamber of the same volume.


Fascinating. Let me see if i understand the ratio,
you said double the diameter, 1/4 the length. That's an interesting gain. Lemme whip something up here. By Volume you meant volume of AIR right?

Diameter of 2 inches. 4 feet long
is equal to,
Diameter of 4 inches, 1 foot long

Is that correct, or am I getting this wrong. BTW pictures in a minute or two.

Picture without the barrel and chamber pipes.
http://filesmelt.com/dl/DSCN2273.JPG
------------
Also, that would be at the SAME psi right? The ratio? I recall you posting a ratio sheet. Let me search this thread for it.

So was Rangorak wrong?

Rangorak Wrote,

"A larger chamber won't reduce performance - and strictly, increase in chamber size will always improve performance slightly.

However, after it's gone past a certain point (which is usually no more than twice the volume of the barrel*), then the performance gains will be incredibly small. All that extra volume (and, more importantly, the extra air to fill it) will just be pointlessly wasted.

* It's about a 2:1 ratio with a really good valve.
With a slower and less efficient valve (like the ball valve you're using), there just isn't enough flow to make use of all that extra air - for that kind of valve, you'd be better off with something more like 1:1 (similar volume of both barrel and chamber)."

Probably spelled his name wrong :P

Currently though this really has to do with my NEXT Gun. I prefer to use the current design on this one, I can just add more stuff in another design.

More emphasis on the current design. anything else I should do besides that brace I'll be cutting with a jigsaw? I don't have one of those cool circle cutting saws (REALLY want one)
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Unread postAuthor: saefroch » Mon Nov 22, 2010 7:26 pm

Yukondano2 wrote:Probably spelled his name wrong :P
This should help you remember.

To insert a quote begin it with [quote=(name in quote, like so: "Ragnarok")] and put [/quote] at the end of the quote.

A larger chamber size(or volume, is what I think Rag meant) won't reduce performance, but a greater volume chamber will always improve performance, if even only by a tiny bit. A greater than 2:1 Chamber volume : Barrel volume ratio is usually considered overkill (for a "good" valve).

You can get drill bits that are designed to cut a large cylinder out of something, not sure what they're called. I think it's a hole saw or something like that.

For your next valve, I'd personally suggest getting a better valve. If you can wrap your brain around how they work, I'd try building a piston valve. And if you're willing to deal with small builds, try metal instead of plastics.
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Unread postAuthor: Yukondano2 » Mon Nov 22, 2010 7:30 pm

saefroch wrote:
Yukondano2 wrote:Probably spelled his name wrong :P
This should help you remember.

To insert a quote begin it with [quote=(name in quote, like so: "Ragnarok")] and put
at the end of the quote.

A larger chamber size(or volume, is what I think Rag meant) won't reduce performance, but a greater volume chamber will always improve performance, if even only by a tiny bit. A greater than 2:1 Chamber volume : Barrel volume ratio is usually considered overkill (for a "good" valve).

You can get drill bits that are designed to cut a large cylinder out of something, not sure what they're called. I think it's a hole saw or something like that.

For your next valve, I'd personally suggest getting a better valve. If you can wrap your brain around how they work, I'd try building a piston valve. And if you're willing to deal with small builds, try metal instead of plastics.[/quote]

I was planning on modding a sprinkler valve. Besides I, don't quite understand the concept of a piston valve. Nevermind that, I want to know if I should start my build of my CURRENT gun. I want to get it done with and over so I can fire it tomorrow. I can look into piston valves afterwords. I could probably build it, and next i want to a relatively Compact gun. I'll talk more about my crazy ideas later. Who knows, maybe I can make it a metal gun since THAT stuff is made to hold pressure. Christmas is coming :D Besides, I doubt Metal is going to Bend like my gun. I can start planning my new gun after this one is completed, I can learn from my mistakes :D.

So, once again, Do you guys think my gun is ready for a build? Or are there any other flaws or things I can fix BESIDES the slow valve.

(BTW, I'm going to see if i can model my guns in Garrysmod, its a sandbox mode and honestly, Google sketch up SUCKS. Its.. ok but its rotation is awful.
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Unread postAuthor: saefroch » Mon Nov 22, 2010 8:52 pm

The rotation in Google Sketchup can be rather irritating, agreed.

A modded sprinkler valve will be better than your current ball valve. However, I can tell you that even a ball valve cannon can be quite impressive at 150psi to a complete newbie (which was me not too long ago).

Don't wish to be rude, but that little "Preview" button next to "Submit" is wonderful. I use it all the time. :P
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