Is it ok to have a rise in an air compressors drain valve?
As long as you purge the tank until the moisture out you should be fine. I maintain some big compressors 150-200 hp that all push up into a separator tank to make sure any oil is removed from the water then the oil drains back to the compressor and this is a commercial setup. I am guessing you have a manual valve, when there is very little water vapor coming out you should be good.