Instructables
video How to Make a Coaxial Air Cannon
This video shows how I make a compact 2" bore air cannon with a coaxial piston valve. To understand how these valves work examine the third animation in the following link:
http://www.spudfiles.com/forums/piston-valves-explained-visually-t8157.html
I also go into more detail of how these cannons function in a video I made many years ago, showing how to build a smaller version using these same principles:
http://youtu.be/9oARDyn4WwE

Warning: It is specifically against manufacturer recommendations to use PVC to contain pressurized air. This video is solely for education and entertainment purposes.

The parts used in this cannon are as follows:
(1) 3' length of 3" diameter pressure rated PVC pipe
(1) 3'2" length of 2" diameter pressure rated PVC pipe
(1) 1/2" PVC ball valve
(1) 1/2" x 2" long threaded PVC pipe nipple
(1) 1 1/2" to 1/2" threaded PVC reducer
(1) 3" to 1 1/2" PVC reducer
(1) 3" PVC coupling
(1) 3" female threaded adapter
(1) 3" male threaded adapter
(1) 3" to 2" PVC reducer
(4) 1" long self tapping screws
(1) brass air compressor tank valve
(2) 3" galvanized steel gas vent tee caps
(1) 3" rubber washer or sheet rubber
(1) 3" tank to bowl rubber gasket

Other supplies and tools needed:
PVC Primer & Cement
Epoxy
Super Glue
TFE Pipe Thread Paste
Coarse and fine Sandpaper
Bench Grinder or Metal Files
Drill & Bits
Bicycle Pump or Air Compressor

Thanks for watching!
pmk2226 months ago

is it possible to use one of those electric instant air valves for this?

Masher0076 months ago

Danger: See link: This is not spam, but a warning. PVC will fail suddenly after a while. This was band member that hurt badly by a T-Shirt launcher explosion.

See the pictures and never use PVC to hold air, Please.

https://fundrazr.com/campaigns/1Zs3c
..

68tobroadway made it!7 months ago

here are some pictures of the muzzle and the piston

Photo on 4-22-14 at 4.59 PM.jpgPhoto on 4-22-14 at 5.02 PM #2.jpg
NightHawkInLight (author)  68tobroadway7 months ago

I have some serious doubts about the strength of that male fitting, it looks like the threads are very shallow. I suggest you cut it off and replace it with a fitting like I show in my video and shorten the barrel as required to compensate for the loss of length.

68tobroadway7 months ago

hey, i have some questions about this. I followed your design almost exactly everything except i had to use a coupling for the 3" female thread adapter because it required it to be attached which i thought would ad a small length to it so i made the barrel just a little longer to match the distance between the end of the barrel and the rear of the chamber in you design i don't know if maybe this is my flaw or that i used something else to make my piston. for the piston i used a 2" pvc end cap wrapped in duct tape to reach the desired diameter to fit in the 3" chamber then used the aluminum tape on the outside and then used a tire seal as a piece of sheet rubber to make the seal and when i pump um the cannon the seal presses against the barrel and holds air nicely and the piston seams to move freely when its not pressurized as in i can move the piston just by exhaling or inhaling into the rear of the cannon but when i pressurize it which i have tried with multiple different pressures from 30 all the way to 70 psi when i release pressure behind the piston all the air escapes out the back and none out the barrel I've thought maybe the piston is trapping all of the air behind it but this isn't the case because when i unscrew the muzzle and try to pressurize it, there is air coming from the chamber like i said maybe this could be because of the distance between the barrel end and the rear of the chamber but i have no clue i thought i would ask for your insight on this I'm a really big fan and have made a lot of your works including the static electricity generator that one is definitely one of my favorites thanks for reading this long message please get back to me as soon as its best convenient

NightHawkInLight (author)  68tobroadway7 months ago

There are three things you can change that will allow your piston to release better. Your problem is that air is not being released quickly enough behind the piston to create a pressure differential strong enough to pull it from the barrel before all the air in front leaks around it. To fix this you can:

1. Make the piston a closer fit so air cannot leak around it as fast.

2. Increase the size or the speed that your release valve opens. This could mean replacing it with a fast acting valve like a sprinkler valve.

3. Decrease the volume of air behind the piston so that there is less that has to be released by the valve before it will be pulled from the barrel. This can be done by using a larger bumper for the piston or doubling it up so as to take up as much volume as possible, or by increasing the length of the piston or the depth of the barrel so there is less space behind it. If the piston is increased in size you may need to remake it out of lighter materials because its weight will negatively effect the speed at which it opens, and it already is probably quite heavy with all that tape.

i forgot also to add my piston is only about 2 inches long

alahlou1 year ago
Hey! Great ible. I was just wondering the ballpark for how much this costs from scratch
I paid somewhere around 45 for everything including the bike pump
chughes1 year ago
Have you considered combining the cannon with a pump like the "...High Volume Manual Vacuum Pump?" Like a Super Soaker, then you would not need to attach/detach a bicycle pump and it would make it a little more transportable.
If I was to use a sprinkler valve instead of the ball valve on the back which way should the flow ????
you would want the arrow on the flow valve to face away from the cannon and i would recommend a modified 3/4 inch sprinkler valve (if you don't know how to mod one there are plenty of videos on youtube) any other questions just ask me on my page. Hope this helps!
I was wondering if you can fire anything smaller than 2" or would you have to put an adapter on it?
dcord1 year ago
This is amazing, graet job! So, potatoes and golf balls. Has anyone tried any other types of ammo? Paint balls or BBs shotgun style for instance. I too would like to tinker with the higher pressures, and plan to use my portable 2 gallon pancake air compressor, but the bike pump is cool too. Thanks!
For paintballs and BBs, you can use the discarding sabot principle adapted to cardboard and duck tape (which btw is my solution for basically everything). All you have to do is make a canister the diameter of the barrel, with one end open and the sides split in half (so that when it exits the barrel, the sides fold away from each other, creating drag and thus discarding the sabot from the paintballs/BBs.)

http://www.milsimlabs.com/ammo.htm
awesomee!
buskrat1 year ago
I found that with my mallow cannon I used thinner rubber and made the piston out of some liquid plastic and now it fires great 40 psi leaves a nice welt at 50-60 feet
buskrat1 year ago
I just recently tried the down size one to launch marshmellows (big kid mallow wars) and I cannot figure out the piston it won't seal to the barrel and when I get it to the pressure only holds for a few seconds do I need the piston to be a tighter fit of is my sealing surface on the end of the barrel the problem?
Randumb831 year ago
Could I make a 1 or 1 1/2 inch barrel instead if so what would I have to change?
NightHawkInLight (author)  Randumb831 year ago
Just the reducer in the front to bring it down to the smaller size.
Randumb831 year ago
How much did this cost?
jimbob19961 year ago
I find that the best projectile for a 2 inch barrel is a golf ball. Works perfectly with my metric 50mm barrel
mudfish1 year ago
beautiful !!!...as soon as turkey season is over...
very well written ,most informative . can't wait to try this.
Half1 year ago
Great air cannon. Just if other people were wondering you can use a simple bike valve instead of the one he has. It can hold a considerable amount of pressure (more or less 100 psi) and all you have to do is glue it on with sealant.
You forgot to list:

(1) 3" tank to bowl rubber gasket.

This is my next spud gun.

In the video you mention only pressurizing to 40psi. Have you tried higher? I regularly go to about 110psi with my sprinkler valve actuated spud launcher.
NightHawkInLight (author)  robertrunyon1 year ago
Thank you, I'll add it to the list. I do go to around 110, but I don't recommend it to people who may be working with PVC for the first time.
cryophile1 year ago
That's a great cannon! What should I do if I want to increase the power?
NightHawkInLight (author)  cryophile1 year ago
To increase the power, adapt the back of the cannon to accept a 3/4" threaded pipe nipple rather than 1/2", and use a sprinkler valve rather than the ball valve. Look up how to modify a sprinkler valve for air use and you'll be in business.
jimmyf1 year ago
Very professionally made ible. Thanks for sharing
Tachyon1 year ago
Nicely done. Thanks.