Today Tuesday the 20th of June I made my first attempt at pressure testing the air tank I made, I setup the test rig outdoors, you can see the layout below.

I attached the tank and its stand to a tree and setup my reinforced camera to watch the pressure gauge.

I used the compressor I made previously to fill the tank with air, the release valve was connected to some string so I could de-pressurise the system from a distance.

When I connected the battery up it started to charge the tank, the pressure increased nicely until it reached 5 Bar, at this point the motors in the compressors really started struggling until eventually they gave out and stopped, this was probably because the batteries couldn't deliver enough current; the compressor draws about 20A when there is no load.
When I was packing up I noticed that the cable connecting the batteries to the compressor had burnt through - that's heavy duty speaker cable.

I am gong to have another go but with an air tank as the supply, I am not going to get up to 15Bar as i wanted but I should reach about 10Bar (the maximum for a tank regulator).