Οιωνός: Another DIY Air Compressor (conversion from fridge compressor)

I never had an air compressor. When I first saw a DIY project about making one out of a used fridge compressor, I started to collect the required components to make one myself. I found a 1/5 hp fridge compressor from an old refrigerator. A friend found for me a 7.5lt used extinguisher. I spent some time reading articles about converting a fridge compressor to air compressor and finally, I picked up the design I thought it was most convenient and practical, made some changes and finally did it.

1. About fridge compressor:
1.1 About using it in such project
These compressors are piston-type, they are silent and provide high pressure. Typical fridge compressors are about 100 - 300 watt, deliver 0.7 - 1 CFM of air and can reach pressures over 500 psi. So, this compressor can be used as airbrush compressor and generally with tools that don't have high air consumption.

1.2 About oil, the problem with wasted oil in open circuit.

Normally, such compressors are used in closed circuits as those in refrigerators. In this way, there is no air humidity and no oil waste as in open circuits.
At first, I had the idea to reuse the wasted oil by using a tube coil (spiral) that would return the oil to the motor with the help of gravity. I hadn't thought of the air humidity which is getting mixed at the output with the oil.

At the end of the day, I understood that I could only separate this oil-water mixture with a filter and periodically replace the wasted oil.

1.3 About electrical relay (Positive Temperature Coefficient-PTC and current relay).
The air compressor was taken from an old refrigerator. It had a PTC relay. This means that the compressor couldn't stop and start at once. PTC relay needed about 30 minutes to get cool.
I tried a mechanical-current relay which could stop and start at once but the compressor was getting hot (something wrong with the technical specifications of current relay I used ?)
Finally, I used the PTC relay that the compressor already had.

2. About extinguisher
I used an old, good condition, 6kg/7.5lt extinguisher. The extinguisher has a head that has four holes. One of 1/4", two of 1/8" and a fourth which is not threaded.

2.1 One hole for all (air input, air output, drainage) - diagram.
I tried to not make any holes on extinguisher body. For this reason, I used all the holes of extinguisher's head. 1) 1/8" for high-pressure release-valve, 2) 1/8" for a high-pressure connector, 3) 1/4" for input and output and 4) Non-threaded hole for drainage.