This is a poorly done instructable but the outcome is great! I will make up for the lack of step by step pictures with a very detailed set of instructions and parts list, I made the whole thing for less than $10.00 US. Money well spent!
Step 1: Fill Valve
The fill valve is installed in the flattest part of the end cap to get a good seal. I used 2 part marine grade epoxy on the inside to seal it as opposed to super glue. It has held for quite some time and seems to be totally air tight. It passed the bubble test, you should put light pressure in the chamber and apply soapy water to all the joints to see if you have any leaks. If there is leaks you will see tiny bubbles.
Step 2: Valve side of the assembly
This is pretty self explanatory by mousing over the picture. I used this combination for a number of reasons, cost and parts on hand played a major part. I am planning on building a new one with a "tee" before the valve and putting in a 1/4inch fit in bushing and attaching an air hose fitting. This will allow me to attach the air hose from the compressor, thus filling the chamber to the pre set amount of air everytime I close the valve! It should work...
I will also take pictures step by step on the next instructable!
I am also planning to make another air cannon out of inch and a half copper, choked down to half inch copper to use with potatoes and other fruits and vegtables...