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My First Build

Posted: Fri Sep 13, 2013 8:54 pm
by CannonBoss
So for a few months I've been putting together a parts list on my pneumatic cannon that I will be building. Here are the specifications:

24" of 2" iron pipe (plan on getting it threaded) to make combustion chamber
2x 2" iron end caps (thread on)
1" ball valve
1" iron fittings (elbow joint etc.)
either a 24" or 36" 1" barrel
Schrader valve

What do you guys think of this plan? What do you think will be its capability? What do you think I can do to improve its design? All help and comments are appreciated. Thank-you :D

Posted: Fri Sep 13, 2013 9:05 pm
by Gun Freak
You only need one end cap because the other side will have reducers to get to your ball valve. Speaking of which, ball valves of that size are pretty hard to open so it won't make a good fast-opening, powerful valve.

You can buy a threaded iron or steel nipple for a pre-made chamber and it will handle the pressure. Also it's not a combustion chamber when you're making a pneumatic cannon (which I applaud you for choosing over a combustion) :D

Also you'll want a barrel at least 3' long; 4' would be better. With a chamber that size you can get away with a bigger barrel!

Posted: Fri Sep 13, 2013 9:18 pm
by CannonBoss
Gun Freak, I actually was admiring your work last night and its wonderful that you've replied to my thread. That being said I meant compression chamber, thanks for correcting me :) The reason I want 2 end caps is because I would like to have the barrel mounted on top of the tank using 1 inch elbows to snake around from the end of one end of the tank so that is is more compact. My search for 2 inch end caps has been really difficult so far... I already have the 2 inch pipe to make the tank out of, and its the perfect size. What valve do you recommend me using? Thanks.

Posted: Fri Sep 13, 2013 10:06 pm
by Gun Freak
Thanks! It's always good to know people like my stuff. You should teach my parents how to do that :D

Anyways... One of us seems to be misunderstanding something. An end cap goes on the end of a pipe and caps it off, and you can't attach anything else to it. My understanding is that you will cap on end, and use a reducer on the other end to go from 2" down to 1", so you can use your elbows. Am I missing something?

Regarding the valve... The best thing would be a piston valve... But they are hard to make and considering this is your first build I don't think it would be a wise decision. They are especially hard to make with metal, and it would be a shame to have a high pressure tank and a plastic valve. Your gun is only as strong as its weakest part.

That said, you can use a QEV... But the ones that can handle high pressure generally stop at 3/4", which is not big enough for your 2"x24" chamber. However, you could always use a 1" diaphragm-style QEV, which would be pretty effective and not that expensive. There was a thread all about them very recently that I'm sure you could look around for.

Before I go any further I just wanna say your chamber is large enough to launch golf balls at a considerable distance. Are you sure you want to use it for a 1" caliber launcher? For such a small launcher perhaps you should use a smaller chamber and save the big stuff for WHEN you decide to go bigger ;)

But I mean... Being that this is your first gun, maybe you could just go with the ball valve just to get the hang of things. You could always spring load it, which would probably double the power and definitely give you better stability and accuracy :)

Once you get tired of that, a QEV or piston valve will be inevitable :D

Posted: Sat Sep 14, 2013 9:54 pm
by CannonBoss
After doing some searches I am unsure about the differences in qev's. I cannot find any 1 inch qev's at all. I guess this all come with experience. So what would be the main advantages if I went qev over ball valve? How far do you think I would be able to launch objects at with this setup and at what psi? Thanks :D

Posted: Sat Sep 14, 2013 10:05 pm
by Gun Freak
I can't give you a range but let's just say with a good QEV and 150 psi you wouldn't be able to follow their flight path or see them land. And it would most likely be invisible to the human eye because it's traveling so fast.

Now, a ball valve's performance wouldn't be all that bad. But if you don't spring load it, the difference between the two valves is night and day.

If you look on McMaster.com you can find larger quick exhaust valves. They get a little pricey in the larger sizes... Also try typing in "dust collector valves".

Posted: Sun Sep 15, 2013 12:21 pm
by dart guy
You can make a qev yourself if you look up how make one on youtube and you can cast it in epoxy for extra strength.

Posted: Sun Sep 15, 2013 1:07 pm
by Gun Freak
You don't make QEVs, you make piston valves. When you buy a piston valve they are called QEVs. But in this case, he is trying to buy a larger QEV, which is actually a diaphragm valve. That is why they are only rated to 125 psi or so.