IOD M02 - Exhaust Valve Air Cannon

Full picture of IODM02 Cannon

Now you are probably looking at the pictures and wondering "How the heck does this air cannon work?" Well I'm going to explain that to you using my own terminology:

  • Air comes in from the rear of the piston.

  • The air pushes the piston into the 2" firing chamber, sealing the opening momentarily.

  • Air now flows around the piston and starts filling the air chamber in front of the piston. Which in turn creates a vacuum on the neoprene, because the air is pushing the neoprene harder into the opening of the 2" firing chamber.

  • As the air pressure increases, the neoprene seal continues to get tighter and tigher. The air will not be able to break the seal if using hard neoprene as the sealer (rated at 1000psi holding strength).

  • Once the cannon is finished pressurizing, the sprinkler valve is opened which "exhausts" all of the air in the rear of the piston. (Which in my case is about 62.8 cubic inches of air volume.)

  • Now all of the air in front of the piston BADLY wants out too. So it slams the piston backward, opening the firing chamber, which allows the huge volume of air to escape out the 2" firing chamber, firing the projectile. (Which in my case is about 546.36 cubic inches of air volume.)

One of the things that puzzled me most when building this cannon was "how the heck does the air get around the piston, if there is no air holes?" Well, I'm still not exactly sure how it works, but the air definitely gets around the piston and fills the air chamber. I know that is does, simply because it uses ALL of the air in the air compressor and requires the air compressor to turn on to fill it up the rest of the way. Not to mention when the cannon is fired, it packs a punch!

How the cannon was built:

Friday, April 16, 1999 --

First off I would like to thank Allen Grahn, who without his help, it would have taken me a long time to get the 3" coupler, 5 3/4" galvanized disks and the 4"x2" bushing all grinded down to fit on the cannon!

The first problem I ran into when scouting out the parts at Eagle, was that the 4" PVC pipe that is labeled 4 INCHES IS NOT 4" ID. It is instead about 3.85" ID. "So what?" Well try to fit that 3" coupler, with an OD of 4", into the 4" pipe with an ID of 3.85." Doesn't quite fit, huh? :) Instant problem. In fact, this problem almost made me cancel my plans to build the IOD M02. That is until my friend, Chris, let me know he had the ability to grind it down.

The next problem was trying to find fender washers that were 3.5" in diameter! The largest we could find were 2" washers. So we decided to head down to NPS warehouse. We figured if anything, we could at least find some metal that we could cut. While looking through all the racks and bins I ran across a pack of eight 5 3/4" galvanized disks. Ah yeah! Went up to the counter to get a price (I was guessing a few dollars) and was told $0.50 for all eight!! Bad Ass!

Now the final problem was getting a hold of some neoprene. None of the local hardware stores we stopped at carried neoprene but at least one of the employees knew what neoprene was and referred us elsewhere. At this point though, it was getting late afternoon, so I would have to wait until tomarrow to followup on the new source.

After all of the running around town trying to find the remaining items, we headed up to Chris's house to work on the cannon.

With the much appreciated(!) help of Chris's Dad, the 3" coupler was put into the metal lathe and the process of grinding it down was started. Scrape, scrape, scrape, etc, etc. This was a very tedious process because the chance that the plastic could warp was high! After about 1 1/2hrs the process was completed and the coupler could slide relatively easily through the entire length of the 4" pipe.

Original and Final Galvanized Discs

Now it was time to cut the 5 3/4" discs down to 3.5." This process would be the hardest, because two discs would be cut at the same time! If the brace on the discs were to loosen at all, it would shift the discs out of alignment and ruin the cut. Not to mention the possibility of damage to the cutting blade and the lathe. The process of cutting the discs took a while, simply because the cutting blade was moved forward EXTREMELY slow.

Finally both of the discs were cut and then trimmed down a little bit to fit in the coupler. With a quick pass under the belt sander the discs were finished!

4x2 bushing used for centering 2inch pipe

Now onto the remaining item to cut; the 4"x2" bushing. This would act as a centering support for the 2" pipe inside of the 4" pipe. This last item I'm guessing took the longest period of time, just because most of the plastic had to be cut away to get to the fins. It really is sad too, because this item went from a value of $4.38 to maybe $1.00. Oh well, at least this way it will definitely center the 2" pipe!

After the bushing was grind down to the fins and cleaning up of all the plastic. We used the mill to remove the plastic sloping of the bushing, so air could pass between the fins.

As you will notice, there are two lips remaining on the slope. Note: A couple days after this picture was taken, I removed them with a metal file.



Saturday, April 17, 1999 --

Well I headed out early in the afternoon to the place I was referred to for the neoprene . . . Damn, they don't carry it in form I need it in but referred me elsewhere. Unforunately that new source turned into a deadend. ARGH!

Now honestly at this point I wasn't really sure what neoprene was, so I decided to find out what it is. After a quick search on HotBot, I found out what some of the uses of neoprene are. Hmmmm, an automotive parts store may carry this . . . So I called up a couple places. None of them carried what I needed, but on the last call I finally got the referral I needed! Just my luck the new place had already closed for the day. Now since their name (EVCO House of Hose) had a generic product name listed, I decided to look up this category in the Yellow Pages. Bingo! I just found a section listed as "Hose Couplings and Fittings," and they are listed in it, along with a bunch of other companies! So I tried calling a few of the other companies listed, but they were all closed. I will just have to wait until Monday now.

Sunday, April 18, 1999 --

Today I started glueing most of the major pieces of the cannon. It sure is interesting glueing 4" diameter pipe! Talk about a lot of glue. I also ended up glueing the exhaust valve firing section together.

4inch pipe section Firing mechanism

I will be holding off on glueing the 2" pipe and its accompanying bushings until the piston is completely assembled (tomarrow is neoprene day!). That way I can be sure everything is lined up correctly. I'm pretty much finished up for today's work. I will be going up to Chris's house later to help him assemble his own air cannon.

Monday, April 19, 1999 --


Piece of neoprene after being cut

ARGH Talk about a suspenseful two days waiting to contact the new sources! First company I call no longer carries neoprene, but they may have some scraps left over in the bin. Called the next company in the Yellow Pages, they don't carry it. Third company, "Yes, we have what you need, come on down." And that is exactly what I did! Success! I have just gotten a 4"x7" peice of neoprene for $1.15!

Damn, this neoprene sure is tough! Theres no way I am able to cut it with a razor blade, so I power up the band saw and cut a 3.5" circle of neoprene. With a drill I'm able to put a hole through the neoprene and push the bolt through.



I'm now ready to assemble the piston . . .

Piston Disassembled

Assembly of the piston
(Instructions of the assembly of the piston follow the pictures)
Piston Assembly - Loose fittings of items Piston Assembly - Verticle standing of items
Loose fitting of all items Partially assembled components inside of piston
Piston Assembly - Rear disc and 3inch pipe inside of coupler Piston Assembly - Rear disc screwed in place (piston is fully assembled)
Rear disc and 3" pipe placed inside Rear disc screwed in place (piston is fully assembled)
Piston Assembly - Front disc placed on top of 3 Piston Assembly - Neoprene placed on top of washer
Front disc placed on top of 3" pipe Neoprene and bolt/washers placed through neoprene

Piston Disassembled

Piston is now complete!


NOTE: Sorry, but its getting late and I won't be able to add the piston design instructions until Saturday afternoon.

Now that the piston is finished, I started working on removing the stoppers from the centers of the 3"x2" and 4"x2" (centering) bushings. That way the 2" pipe will be able to slide through unobstucted. I started off with a razor blade and when that was going too slow, I grabbed a metal file and really went at it (not to mention my thumb and ring finger. :))! I then used some sand paper to smooth out the rough areas. Took a while but I finally got both bushings ready and they slide up and down the 2" pipe.

A little side note: Well I decided to do some quick pressure tests (about 35psi) to see if the piston would seal on the 2" chamber (and hopefully fire), before I glued the front bushings. So I tapped the 3"x2" bushing into the 4"x3" bushing using a hammer and started pressurizing the cannon. The piston did a little "thump" and seals the firing chamber. But not only does it seal the firing chamber, it starts pushing the 2" pipe through its bushing! Talk about force! I ended up pushing the front of the firing chamber into the back of the car tire and on back end I braced it with my foot. Umm, well, that didn't work. It started pushing my foot backwards. :) . . . So I ended up aborting this test and hoped everything would work come tomarrow.

Next thing on the to do list was to cut a 3" section of the 2" pipe. Using a hacksaw I cut a 3"x1/4" screw to 2 3/8" and used a sanding belt to smooth the rough areas. I then drilled a hole in the 3"x2" pipe about 3/8" from the end and pushed the screw through the pipe. The 3"x2" pipe was then glued into the 2" coupler and the remaining 6' 9" section of 2" pipe was glued in the other end of the coupler. The 4"x2" centering bushing was now slid down the 2" pipe until it reached the 2" coupler.

2 inch pipe, coupler and centering bushing Bolt inside of 2 inch pipe and coupler

Now it is measuring time. Since I was able to slide the 2" pipe through the 3"x2" bushing, I pushed the 2" pipe from the front of the cannon, all the way through the 4" chamber, until it reached the female adapter in the rear. The piston was then placed in the rear of the cannon and pushed until it hit the 2" pipe (almost instantly).

Holding the 2" pipe steady, the 3"x2" bushing was slide (tapped lightly with hammer . . .) down the 2" pipe until it reached the 4"x3" bushing. The 3"x2" bushing was then tapped into the 4"x3" bushing lightly, so that it now hold tight while I push the 2" pipe forward using the piston, until the piston was at the perfect position (the perfect position for me, was about 2 1/2" from the end of the 4" pipe). I now measured how much space I would lose when the front two bushings were sealed, male/female adapters screwed in, and from the vinyl bumpers put in place. The 3"x2" and 2" pipe was now removed and the bushing was slide towards the rear end (the end the piston hits!) five inches, to compansate for the lost space. This would leave the piston with 2 1/2" of movement when everything is all sealed (NOTE: I need to measure it once again to make sure that is accurate, now that the cannon is finished).

So now I marked with a pencil where the bushing had to be when glued and also marked a spot 4" beyond that as a reference point. The bushing was then slide forward about 3" from the final point and glue was applied to the pipe and the inside curved area of the bushing. Unfortunately when I finished glueing, I found the glue was drying a bit to quick before I could pull the bushing down to the correct space. So the pipe was stood vertically quite rapidly and the bushing was yanked down hard and then pushed back up into the correct spot. Needless to say, about 9" of the pipe is now "blue." :)

One of the trickiest parts to glue was between the 4"x3" bushing and 3"x2" bushing on the front end (hardware store was currently out of the Sch40 4"x2" solvent bushings). Since the 2" PVC pipe was already going through the 4"x3" bushing and could not be removed, the 2" pipe ended up with a second coat of glue while trying to glue the 4"x3" bushing. At this time I'm not certain if I have a solid seal between these two bushing's. I will know once I get some TFE paste to seal the front 4" male adapter. If it's not a solid seal, then I will have wasted about $15 of hardware. ARGH!

Front of the 4x3 & 3x2 bushing Rear of the 4x3 & 3x2 bushing (notice all the blue glue!)

NOTE: All PVC parts in the following item lists MUST BE LISTED AS SCH40 OR HIGHER! Thin wall PVC pipe will not work and has a higher chance of rupturing at high psi. BE CERTAIN the 4" reducing bushings list SCH40 somewhere on it (usually on the lip). When I was at Eagle, I found a lot of non-SCH40 4" reducing bushings. The bushing should almost be a solid piece of plastic with large supporting "fins". The non-SCH40 bushings almost look like a 4" cap with a 2" hole in the center!

Key: S = Solvent connection, T = Threaded connection.

Items needed for air and firing chamber:


5ft. 4" PVC $9.45 1 $9.45 Eagle Hardware
7ft. 2" PVC $3.47 1 $3.47 Eagle Hardware
4" Female Adapter SxT $4.47 2 $8.94 Eagle Hardware
4" Male Adapter SxT $3.98 2 $7.96 Eagle Hardware
3" PVC Coupler SxS$2.16 1 $2.16 Eagle Hardware
2" PVC Coupler SxS$0.64 1 $0.64 Eagle Hardware
4"x2" PVC Reducing Bushing SxS $4.38 1 $4.38 Eagle Hardware
4"x3" PVC Reducing Bushing SxS $4.38 2 $8.76 Eagle Hardware
3"x2" PVC Reducing Bushing SxS $2.06 1 $2.06 Eagle Hardware
3"x1" PVC Reducing Bushing SxT $2.08 1 $2.08 Eagle Hardware
2 3/8" long, 1/4" metal rod $0.00 1 $0.00 Already had

Sub Total: $49.90

As you noticed, I ended up having to get some 4"x3"/3"x2" reducing bushings. The first Eagle Hardware only had ONE 4"x2" SxS SCH40 bushing and about 15 garbage non-SCH40 bushings. The second Eagle Hardware (across the city) only had garbage non-SCH40 bushings. Not only that, but when I called to confirm they had the correct item in stock, the guy confirmed they had lots of the 4"x2" solvent bushings. YEAH, RIGHT! All they had was 4"x2" solvent to threaded bushings. ARGH! I wish I knew who had taken the call.

Items needed for firing mechanism:


1"x6" PVC Nipple $0.47 1 $0.47 Eagle Hardware
1" PVC TEE SxTxS $0.85 1 $0.85 Eagle Hardware
1"x1/2" PVC 90 Reducing TEE SxT $0.58 1 $0.58 Eagle Hardware
1" PVC Street 90 ELL SxT $0.76 1 $0.76 Eagle Hardware
1" Electric Inline Solenoid Valve TxT $8.99 1 $8.99 Eagle Hardware
1/2"x3" PVC Nipple $0.32 1 $0.32 Eagle Hardware
1/2" Galv TEE $0.57 1 $0.57 Eagle Hardware
1/2"x1/4" Galv Bushing $1.19 2 $2.38 Eagle Hardware
1/4" Pressure Gauge 200psi $3.00 1 $3.00 NPS warehouse
1/2"x3 Galv Nipple $0.48 1 $0.48 Eagle Hardware
1/2" Ball Valve $1.00 1 $1.00 NPS warehouse
1/2" Teflon Tape $0.96 1 $0.96 Eagle Hardware

Sub Total: $20.36

Items need for assembly of the piston and bumper:


1ft. 3" PVC $1.79 1 $1.79 Eagle Hardware
3" PVC coupler SxS$2.16 1 $2.16 Eagle Hardware
Galvanized steel discs $0.0625 8 $0.50 Found in metal salvage bin
3" long, 1/4" wide bolt $1.09 1 $1.09 Eagle Hardware
1/4" nut $0.26 1 $0.26 Eagle Hardware
Small washers $0.14 2 $0.28 Eagle Hardware
Medium washers $0.17 2 $0.34 Eagle Hardware
1/8" Hard neoprene with cloth insert $1.15 1 $1.15 All West
2ft 3/8" ID Vinyl tubing $0.64 1 $0.64 Eagle Hardware
1ft 5/16" OD Vinyl tubing $0.11 1 $0.11 Eagle Hardware

Sub Total: $8.32

Items needed for ram rod:


10ft 1" PVC Pipe$1.69 1 $1.69 Eagle Hardware
1" PVC Cap $0.24 1 $0.24 Eagle Hardware

Sub Total: $1.93

Total Cost: $80.51

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