Air Tool Dos & Don’ts

Welcome back to Dad’s Workshop! I wanted to cover a couple of related subjects, They are all about pneumatics; air tools and compressors to be specific.

In some people’s minds these amazing tools are mystical magical apparatuses that somehow convert moving air into another form of energy. When it all comes down to it, most air tools function in one of two ways: they are ether a windmill or an over-pressure valve. They’re that simple.

How Air Tools Work

Take an air drill for example: a small cylinder that has maybe five or six slits along the long axis, and the same number of fins set into the slits. That assembly is then slid into another cylinder with very close tolerances between the edge of the fins and the outside cylinder. Air is introduced into the cylinder perpendicular to the fins causing them to rotate the inner cylinder in the direction of airflow. The more air, the faster the inner cylinder spins.

Those mechanically-minded types are already thinking about all kinds of stuff much more advanced than I am going to discuss here, like forward-reverse switching, variable speed valves and so forth. There are more parts in making something like an air dill work, of course; valves, gears, gaskets, seals, o-rings, and the like, but the basics are those concentric cylinders and the fins at the heart of it all.


Because of the close tolerances any debris or binding will cause catastrophic failure. Most of the time the fins are made from fiberglass or something similar, carbon fiber is common too. Even though the materials are strong, the parts are small and thin, they are also spinning very fast. The fins are lightweight and the cylinder is comparatively heavy so the rotation builds up a lot of inertia. If a small sand-sized particle gets into the chamber, pieces of fin can and most likely will impact them and bits will break off, adding more loose material and causing a cascading failure. This can also happen with binding. If a fin hangs on the wall of the chamber for some reason, like gummy oil or a moisture build up, it drags the fin weakening it until it breaks, leading us back into another type of cascading failure.

This might make air tools sound a little too touchy for the average tool user, and they can be. The biggest part of taking care of air tools is in understanding them; how they work and what causes problems. Take the time to read all the paperwork and look closely at the diagrams and parts list. We have already covered several of the potential problems. Air tools that are susceptible to particulate damage usually have a small screen filter to help, but you can do a lot by keeping particulates out of your air hose. Hook up a blower tip and just blow out the hose before attaching it to a tool; that will go a long way in preserving your air tools right there.

Air Pressure and Air Tools

Another tip for keeping your air tools in good shape is to pay attention to the manufacturers pressure specifications. If the specs give you a pressure range, say 30 psi to 70 psi, stay in that range. If you are dialing in your pressure for a nail gun, start on the low end. The pusher should drive the nail just below the surface for finish nails or flush to the surface for head nails. If you are using another kind of tool start in the mid range, say 45 or 50 psi in that 30-70 range. If you need more oomph, kick it up a little. If it can be dialed down, then dial it down a little. Never exceed the maximum pressure specified! This will only degrade the tools performance and will likely damage something the key here is RTFM.

Air Tool Oil

O-rings and seals in air tools are at very close tolerances. Too much air flow will blow them out causing metal-on-metal stresses that will damage the tool. Some people think that by applying a lot of oil to their air tools they are helping them work better, smoothing things out. In truth, they are damaging them. An over-oiled tool is more likely to blow out seals and rings. An over oiled tool builds up more pressure than it should and may unseat seals and rings causing them to dislodge. Either way it is not good for the tool. Here is another RTFM moment. If the manufacturer says two drops of oil in the air inlet after 4 hours of work, they mean TWO drops after FOUR HOURS. Not a squirt, or “I’ll get it later.” This is very important.

The problem arises for most people when they don’t understand what that means. In a consumer-grade tool, follow the directions and don’t use the tool in a construction environment. In a construction-grade tool used in a consumer environment you need to pay a little more attention. A roofing nailer that says “four drops of oil at the beginning of the day” means a full day of continuous use like a roofer would. If you are roofing a dog-house, dial it back a bit. If in doubt, many manufacturers have customer support lines, give them a call and tell the service department you have a question about oiling, make sure to tell them how much you are actually using the tool. They should be able to help.

Most air tools that need oil come with a small squeeze-bottle of air tool oil. Read the manual for specifics about what oils are safe in that particular tool. If not specified, a generic air tool oil can be used. Only use oil specifically designated for use in air tools. A little side note: That tiny bottle of oil, if used properly, it will usually last a lot longer than you might think. Again RTFM.


This brings me to automatic oilers. For the average consumer tool user they are a waste of money. They are designed for shop use at a work station, one tool, same air pressure, all day. If you change tools or change the pressure you need to re-calibrate the oiler. Another consideration is that not all tools use the same oil. Most do, but the few that don’t, really don’t. It really is more of a pain than just putting in a drop of oil before stowing the tool. Another consideration often forgotten is that oilers put oil into your air line as well, and some tools don’t need, or can’t have, oil run through them. Clean dry air is all you want in your air lines and in your compressor tank. Oily air attracts particulates that build up. Eventually a clump of oily crud may find its way into your air tool, and for some reason it’s always the new expensive tool you just got that gets hit with the crud-clump. Save yourself the headache and the money.

Tank Rot

Which brings me to Tank Rot. Compressors are susceptible to tank rot in part because they are rarely kept in environmentally-controlled places. This means that the temperature will range widely, especially when the compressor has been in use. The wide temperature fluctuations tend to cause condensation in the tank which leads to rust, commonly referred to as tank rot. A good water separator on you main tank outlet will spare your lines, hoses, and tools, but it can’t help the tank itself. You shouldn’t put oil in the tank to prevent rust because it will end up in the air, then the lines, hoses and tools. Oil can get past some of the water separators and will clog others, so you are better off not doing that.

I have seen some success from people who removed everything from the tank and poured some oil-based paint inside and rolled the tank around slowly for a couple of hours making sure that the entire tank interior was covered then draining off the excess. This is a difficult process though. It requires an acid cleaning in the tank, thorough rinsing and drying at least cycle. I have seen it need two or three cycles of prep work before the tank was ready for paint. This all needs to be done on a new tank, it really doesn’t work well on old tanks. All in all I don’t think it is worth the trouble. The bad part is that you have introduced potential particulates and cracks in the paint become moisture reservoirs and end up accelerating tank rot not stopping it.

The best way to combat tank rot is to discharge all of the lines and the tank at the end of the day through the bottom valve and leave the valve open until you are ready to use the compressor again. If you think it will be a long time before it will be used, a rubber band or string and a piece of cotton cloth tied over the opening will allow air and moisture through but not critters. When the air in the tank is able to contract and expand with the outside air it is less likely to have condensation.

Wrap Up

So the basics are:

  • Look at the diagram or breakdown that came with the tool and see how it works and what the failing points are likely to be so you can prevent them.
  • Only clean dry air should go from the tank to the tool.
  • Use only the specified pressure range.
  • Use only air tool oil and use it the specified quantities.
  • Discharge the entire air system when not in use

See you next time,