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I started my woodworking career with a quarter-sheet electric sander, quickly graduated to some random orbit electrical disk sander and eventually realized that I could significantly shorten sanding time with an atmosphere palm sander. I depended on a 5" Dynabrade sander and Sears 3HP air compressor. It would run out of air pressure almost immediately and the air sander would slow down to the point of being useless. I would then have to wait for several minutes for the pressure to build up again to get another minute of sanding.
To make matters worse, I had three people hired as sanders and so I would need to keep three machines running at top speed all day long. I did some math and discovered that I would need a ten horsepower air compressor with a large tank to do this. I was lucky to find a used one for not too much money but it required three phase power and lots of it.

Air sanders are aggressive and efficient. They are light in weight when compared to their lesser electric cousins. My sanders took to them immediately and production took off. I was as happy as they were. Soon there was another machine besides the air compressor required having large amounts of air in the shop: an Onsrud inverted pin router. It was also great to be able to blow sawdust of benches and machine while cleaning upon the shop at the end of the day. The compressor was also used to spray finishes on the completed furniture.
Years later, I built a smaller woodworking shop in my home which only required one air sander running at a time. For that shop, I purchased an air compressor half the size and isolated in a soundproof room in one corner of the shop. I ran 3/4" galvanized pipe below the shop floor to three regulators at three different convenient locations. The machine I purchased for that shop as a 5 HP Ingersoll Rand model using an 80 gallon tank. In the 80 PSI required by my Dynabrade sander, the compressor would produce enough atmosphere all day long. I have to say that this compressor was well constructed. All I had to do was keep an eye on the oil level in the glass. At nighttime, I would turn off the master air valve on the face of this machine, leaving the electricity on, to quiet the compressor for the evening.
I must suppose that, having read this far, you've got some interest in using a air compressor to power air tools in your shop. Most likely, a 2-stage reciprocating air compressor may fulfill the requirements of a small to moderate shop. As a rule of thumb, a 5 HP air compressor will power a single air compressor, a 7.5 HP machine will power two and a 10 HP machine is going to be necessary for three sanders.
The size of the compressor's air tank is an important consideration: The bigger the tank, the more frequently the compressor will want to cycle on and off, This is hard on both the motor and compressor pump over time and it uses more electricity. I would never even look at an air compressor used to power an air compressor with less than a 60 gallon tank and I would feel far more comfortable with an 80 gallon tank.
The type of electrical power required by an air compressor is another consideration. In case you've got three-phase electricity available at your location, fine. Three phase motors tend to utilize electricity a little better than single-phase motors. Large air compressors will all require 3-phase power but the 5 HP models come either way. If you don't have 3-phase energy available, you can fabricate it with a rotary or digital phase converter as I did in my smaller store. Whether you use three or single phase power, you'll need 230V AC electricity for single-phase motors and 208 or 220V AC for the three-phase selection. Be sure to check the voltage and amperage needs of almost any air compressor before you buy it. Electricians can be expensive.
A two-stage compressor pump is a must to get a machine of this size. Two-stage machines have two tanks, one bigger than the other. Air is first introduced to the massive cylinder where it's partially compacted and sent into the more compact cylinder for final compression to the tank. As air is compressed, heat is created and thus a good machine will always have a finned intercooler built in.
Compression not only produces heat but squeezes water from the atmosphere which ends up in the tank. Tanks can rust internally over time and if this is not kept in check, the rusted air tank may finally burst causing tremendous damage and even death. That is why it is critically important to drain the tank of water every single day. Most machines come equipped with a drain valve at the bottom point of this tank. If you do not want to spray water over the ground under the compressor, you might want to think about piping it in the valve into some other location like beneath the floor or to a drain. Piped water will flow into a sink since it is being pushed from the tank by compressed air