The majority of sanders used with small, at home projects are electric, but for the right application pneumatic sanders provide distinct advantages. Because they contain no motor, pneumatic sanders are lighter, making them easier to operate for long periods of time or at an awkward angle. Typically, pneumatic sanders are orbital, meaning they use air to quickly oscillate a ball bearing causing the abrasive pad to move randomly. This random movement leaves less noticeable markings on the workpiece.
The simplicity of the the pneumatic design allows for longer lasting and more cost effective tools. Pneumatic equipment will also generally provide more force than the electric equivalent. Also, because pneumatic sanders require compressed air lines, it is easy to incorporate a suction based dust collection mechanism, a must-have in some industrial sanding environments.
The biggest downside to a pneumatic sander is the large amount of compressed air that they consume. In order to run a medium sized pneumatic sander, you will want to supply 90 psi of air at up to 17 cfm. To run this for the duration of a typical application, you should have at least a 60 gallon tank, the size of a typical large mobile compressor. This means that pneumatic sanding is probably not feasible for hobbyists working out of their garage. However, consider a pneumatic sander for better quality and price in industrial application where large scale compressed air lines are readily available in the shop.
I've identified 3 good options for different needs, let's look at some specs:
Best Budget Option
CP870 by Chicago Pneumatics
The large pad sizes lends versatility to this affordable sander. Its heavy weight and lack of vacuum mean that it will not be good for industrial applications where you will be sanding all day. However, it is a high quality product that will perform well for smaller projects. It can produce 10,000RPM and consumption tops out at 18CFM of 90PSI, making it a suitable for people with mobile compressors. At this low price tag, it is a great deal.
Best High Performance Option
38494 by 3M
With a small 3 inch pad size sander and no vacuum, this sander will not be good for messy applications that put off a lot of dust. This is a very high quality product designed for high precision industrial environments.
Best Overall Option
4151-5 by Ingersoll Rand
This sander is a great overall choice. Running off an average 8CFM at 90PSI, this sander is definitely viable for mobile compressors. Yet at 12,000RPM, equipped with a vacuum, 3.25lbs and a comfortable ergonomic design, this all around impressive pneumatic sander is an excellent choice for industrial applications as well as small projects.