moisture porblem

All air lines should have something like this installed:

http://www.kellerproducts.net/compressed_air_filters.html

Read #2 again. That is a very well designed air system. What is missing from your system?

A good answer starts with a good question. How much compressed air? What pressure? How long is the run before the compressed air is used? What is the air used for?

For painting it is common to install filters right at the air gun. If there are long runs of compressed air pipe, it is common practice to install water separator-filters at each outlet along the pipe. Again, a good answer starts with a good question.

The easy answer to your first question is: if water comes out when you spray or use your compressed air - you can know you have moisture in the compressed air. Obviously you are having a problem with this or you wouldn't be posting this question. When you compress air that has water in it, you get compressed air with water in it. In fact, if you compress air to 6 atmospheres, you get 6 times as much water in it as compared with the ambient air.

There are facilities one designs into a compressed air piping system for low volume that should get the water out of your air. These are called water traps. These are usually vertical pipes set up at low points in your main pipes that allow you to manually or automatically drain the water out of your pipes where it collects. It works in low volume applications because the water will come out of the air as it cools (usually it's hot at the compressor so it will hold more water). If the volume of air is too high - meaning the air from the compressor does not have time to cool, and thus condense the water between the time it is compressed and the time it is being used, there is still hope, though it is more expensive.

The solution at that point is refrigerated air dryers. This is a refrigeration unit that cools the air as it passes through a coil (relatively slowly) and gives you relatively dry air. Google "Refrigerated Air Dryer" and you will find several manufacturers that supply these.

The general rules of this game are that you need to define how much water you can live with in your processes and you need to know how much compressed air in volume (cubic feet per minute) and at what pressure you need to have it dried to your tolerable moisture content. The more air and the drier you want it, the more it's going to cost you to get there.