Electric air compressors are the most common source of compressed air in permanent installations. The smallest models run on standard 110v, single-phase power, but most commercial and industrial models need three-phase power. Often, you’ll be able to specify the voltage (208v, 230v, 460v) the compressor should run on, so make sure you know what you have available.

There are two main types of electric air compressors to consider:

• Reciprocating air compressors – In these machines, also known as piston-driven compressors, pistons compress the air in a cylinder and force it into a high-pressure storage tank. Piston-driven machines are the oldest and most affordable type of electric air compressor.
• Rotary air compressors – Instead of using pistons, rotary compressors use twin screws, like two oversized drill bits next to each other, to force air up into higher pressures. Until recently, rotary machines were considerably more expensive than reciprocating models – now, prices are becoming more and more competitive.

An important way to decide between these two is to consider whether your application is continuous use or intermittent. A nail gun, firing a burst of air every few seconds, is an intermittent tool, while a spray painter is used continuously. If your electric air compressor will be used continuously, you’ll want a rotary compressor.

This is due to the rated “duty cycle:” the amount of time each hour that a compressor is able to work. A duty cycle of 75% means the air compressor needs to rest for 15 minutes out of every hour to cool down. Rotary compressors have a duty cycle of 100%, thanks to fewer moving parts and robust oil cooling systems. In contrast, reciprocating compressors are designed to run only part of the time.