Three phase air compressors are for workshop, heavy duty and industrial use. The difference with a three phase compressor is it's power supply. It will run from a 415v 3 phase as opposed to the conventional 230v that you will find in your home. This power supply is completely different from the standard 230v and the one cannot be made into the other. The advantages of having an air compressor that is 3 phase is generally power. Because of the higher voltage, the motor can be much larger and more powerful meaning that these compressors will be able to produce a lot more air.
Tank Size: The bigger the tank the more air you can store and the less your motor and pump will have to work. Make sure whatever you buy will fit in the place you want to keep it.
Motor Power: The bigger the motor, the quicker your compressor can build up air and the higher the level that air flow can be kept constant at.
Voltage & Ampage: Make sure if you are buying a large Industrial Air Compressor that you buy the correct voltage, 400v is a three phase, electricity supply, so make sure you have this installed or are prepared to get it installed before buying. Some 230v compressors will run from a higher ampage (e.g. 16A, 18A or 32A) due to their motor size, this is not a big job to install, but will require an electrician if you do not already have it. 230v 13A can use a standard household 3 pin plug.
Piston Displacement & Free Air Delivery (F.A.D): These are both measured in CFM, but piston displacement is the volume of air produced at the pump and the free air is the actual volume of air that the compressor will produce (F.A.D is usually around 25-30% lower than the piston displacement).