If you are working with air pressure you generally need somewhere to store the air pressure that you have built up so that it can be used elsewhere or at a higher rate than the compressor can deliver alone.

I spent a while looking for air tanks but there didn't seem to be anything out there apart from very large commercial cylinders and paint ball gun tanks although I did come across a site which mentioned making one out of a fire extinguisher.

With this in mind I discharged a small dry powder extinguisher I had lying around and unscrewed the top, once it had been cleaned out (be careful the power is very fine and gets everywhere and tastes awful) I set about deciding how I would attach to it.
A quick trip to B&Q produced a brass reducer designed to convert a 1" thread to a 1/2" thread, after some grinding down of the outer thread it fitted nicely into the opening of the tank. Simply smear some epoxy around the thread and bake for 10 minutes at 100-150oc and you have an air tight tank (or at least theoretically).

This is when I learned the difference between a standard thread used with compression fittings and proper air tight fittings. The thread on compression fittings is designed to hold the copper pipe in place, this creates the seal not the thread, after wasting a fair bit on a variety of valves, T joints, nipples and reducers I decided to look through the RS catalogue for the proper stuff.

After looking through the thousands of different fittings for half an hour I had made up a nice order or valves, T joints, nipples and reducers, hopefully this time they would be the right ones.
Thankfully they were but this did mean I needed a new air tank one with a proper thread, this time I bought a larger dry powder fire extinguisher once again I ground down a reducer to fit and baked for 10 minutes.

The tanks are rated at about 15-20 bar maximum so they suit the compressor I put together perfectly.

Before I start doing anything with it I needed to pressure test it to make sure it wasn't going to blow up in my face, to do this I created a frame to hold the tank, a pressure gauge, safety value and connection to the compressor. The compressor would be activated from a distance and charge the tank up to about 15bar at which point it would be turned off, the tank should then sit safely without leaking or blowing up, after a couple of minutes I would use some string to release the valve de-pressurising it.

The air tank pressure testing rig

Pressure testing tank valves

The image to the right shows the top of the test rig in more detail, you can see the pressure gauge connected directly to the tank and the release valve connected up via some string; the adapter on the left is a quick release coupling, these allow the air supply hose to be disconnected without breaking the seal and de-pressurising the tank.

My attempt at testing the tank