Not Ranked
Hauss,
I thought you were asking for confirmation that what you were doing was not going to cause a problem. I did not realize you were trying to educate the world that leaving air in the compressor tank is fine and therefore a waste to drain.
Your premise that the more air you pump into the compressor the more moisture you pumped in is true, but that does not apply to a static tank of trapped air. A static tank of trapped air at 10 bars of pressure has about 10 times as much air in it as an empty tank at 1 bar (atmosphere). Also the higher the air pressure the higher the dew point. So when you leave the tank pressurized, it has more air in it with a higher dew point temp. It is more likely for water to form condense, if it is left with air trapped in it.
Your stating that by leaving air in it you would have less moisture is miss leading at best. The next time you start the compressor up and it does not have to pump all that air back in, then at that point in time you have put less air into the compressor. However when you shut it down and let it sit, there was more moisture in the tank while it sat, than it would have had had you blown it down.
When you stop the compressor, the air that is in the tank has had it temperature (adiabatic compression) and the dew point temperature increase. As the air temp drops, moisture forms when the air temp drops down to the dew point temp. You blow that moisture out. If you then blow down the tank to 0 PSIG. The dew point of the air in the tank drops with pressure. Now the remaining air in the tank is much drier than the air was when you pumped it into the tank. Remember you pumped air in and then blew water out, so that air absolutely has less moisture in it. While it is still compressed, it remains very close to the dew point temp. After it is decompressed it is much drier.
So I disagree that leaving the air in the tank is actually putting less moisture in the tank, while it sits. It is not the best way to leave the tank. It is always going to be less chance of moisture forming in the tank if you blow it down and more chance if you do not.
I still think you are fine. I would not recommend doing this in an area where the temp may drop below freezing, after you shut the compressor off. I have seen chunks of ice form.
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