Air tools are powered by pressurized air provided by an air compressor. The process of compression gives off moisture. Some of this settles around the rubber o-rings and becomes a sticky buildup that robs the tool of its performance. Oiling the tools the right way gets rid of the sludge. C.L Rease has authored an easy to follow guide on how and when to oil your air tools.
Lubricating oil specially formulated for air tool use is all you need. However, remember to use oils that have a label specifying they are for air tool use. To start off with the oiling process, invert your air tool so that the air fitting faces toward you. Fill the fitting with oil and depress the trigger to allow the oil to enter the tool. Next, join the air line to the tool with the outlet pointed toward the ground. Depress the trigger and let the tool run until the oil stops flowing out.
To keep your air tools free from sludge, it is advised that you oil them before each use.