I just got a new air compressor for occasional finish nailing and tire inflation. I understand that I need to open the bottom drain to let out any condensation (i.e., this question) after each use.
Should I also store the compressor with this valve open? Is it a bad idea to do so? If it makes a difference: I only plan to use it once or twice a month and live in a very dry climate.
Leave the valve closed during storage to prevent moisture, dust, and insects from entering the tank (as @Scivitri wisely mentions in his comment).
Even though any additional moisture could be drained form the tank later, it's more difficult to get the dust and insects out. And they're what's likely to clog up any attachments. They'd also potentially clog the drain valve itself and essentially cause a slow leak until they were removed.
Directly from owner's manual (Central Pneumatic 6 gallon model 67696)
Drain tank of moisture after each day’s use. If unit will not be used for a while, it is best to leave drain valve open until such time as it is to be used. This will allow moisture to completely drain out and help prevent corrosion on the inside of tank.
Should be covered in the owner's manual if you can find it. The manual for mine says to leave the valve open in storage. Presumably to let the internal/external environment stay equalized to minimize condensation.
I have always drained my compressors perhaps three times a year , and use it quite often. Depending on the air temp outside, and if it goes down under the freezing temp, I leave the valve open, just in case there is condensation in the tank, but most of the time there is none that comes out after use. Does not make sense to me to leave the valve open at all. Keep the contaminants out of the unit. Chances are that it will do more harm to the inside that prevent anything else.
I did scuba diving for years. The general rule was to always leave a minimum amount of air pressure in the vessel, when not being used, so that moisture, or anything else, could not get into the tank. This sounds like good advice for any pressurized vessel as moisture is the #1 cause of corrosion/damage.
