First things first; in order to get an air cannon to release enough air to make that large startling sound, we'll need an air trigger that can pass a massive amount of air at once. The air valves used on air cannons typically cost about $50 or $60. To keep our costs under *totally ridiculous*, I turned to the washing machine water valve that has been used for air valves since Carl Chetta of the Trash Can Trauma fame introduced it's creative use some time in the 1990's. I was determined to use one for my cannon, but I knew it would take some work, as the valve you see above without modifications will not expel enough volume to scare much of anyone. The particular brand and or model valve above wound up being the very best one out of many different ones that I had to test to bring these plans to this web page. This translucent white unit I purchased many years ago in a bag of 10 random valves is a Horton C539 / N-6042 model and was the only one I have EVER seen. Since I found it impossible to find another like it I knew that the likelihood of you finding one was between slim and none as well, so I needed an alternate that you could use for a good result. 

   Luckily, the most abundant of all the water valves used, model #N-51 (which is usually blue in color, but can be found in others as well) can be modified to work just fine. Whether it is stamped Maytag or some other manufacturer's name, the N-51 is the model. And it is the ONLY other model I could find that would operate under the pressure needed to make this project work.

  Note; There are other plentiful valves out there besides the one we recommend here, the N-51, but the big difference is they read N-50 and they DO NOT work at this pressure. I am stressing this point so that you don't waste your time with dishwashing valves or some other type than the two I show here, as after dozens of different tests I have yet to find even one that will do the job when placed under more than 50 lbs of pressure.  

  You can find these at many appliance repair places for $3 each. Beware here; I had some repair guys wanting to charge me up to $10 apiece until I informed them that the going price all over town was $3. So don't be afraid to haggle. Remember, half the fun of this project was building it for only $20! You could also go to the local scrap metal recycler and ask to salvage one off of a machine that has been tossed and save some money. These will cost you only $1 and are really easy to remove. Don't bother trying to buy one new, as these are typically $35.

    $20 isn't a lot of money. Not even to a homeless person, so don't expect a huge shopping list. Moreover, this is a project that should take you only about a half an hour to complete. In this photo you can see everything needed to make your $20 Air Cannon's air cylinder minus the tools you will be using. This is a single-shot cylinder for the cannon, so if you plan to trigger yours twice in rapid repetition you should increase all of the 2" fittings here to 3" fittings which will give you enough for two full firings. You will notice right away I am showing a 1/4" close fitting and female air coupler instead of just a male coupler, and that is because I didn't have the male during this photo layout. It will work as well either way. The tools you will need for this project are a heat gun or lighter, a drill, a 3/4" drill bit, 3/8" drill bit, electrical crimp tool, two monkey wrenches, a die grinder and a crescent wrench.

SHOPPING LIST (total should be almost exactly $20)

(1) 12" length of 2" galvanized pipe
(1) 2" galvanized pipe end cap
(1) 1/2" to 2" galvanized pipe reducer
(1) 1/2" to 1 1/2" galvanized pipe reducer
(1) female hose to FIP swivel fitting 3/4" x 1/2"
(1) lawn hose end cap
(3) 1/2" short threaded nipple
(1) 1/2" galvanized pipe T fitting
(1) 1/2 to 1/4" galvanized reducer bushing
(1) 1/4" IID male air coupler
(1) 6' extension cord
(2) 1/4" female quick slide, 18 ga. crimp cord fittings
(1) washing machine water valve

   In the next section we will assemble our crazy invention!