75dually
+1y
Basically it removes the oil from compressed air coming from the compressor. York 210 pumps, like what I plan on using, tend to send a little bit of oil into the compressed air stream, and it is best if it gets removed before it reaches your air tank. You want as clean and dry of an air supply as you can get so that your valves function properly. I also have on order an moisture separator as well. The 2 together make a really good air filtration system.
Here is a good York 210 build to see what a total system can look like and all the other parts required to have an air supply like this on a truck.