Most compressed air systems have common features. There is an air compressor to produce the air, a receiver/tank to store the air, drying and filtration to prepare the air for use, and pipe-work to distribute the air. There will also be oil water separators to treat the condensate leaving the air compressor, receiver, filters and dryer.

Fixed Speed Compressors

 The air compressor will deliver a set flow rate of air, normally measured in cfm or m3/min, at a specific pressure (bar or psi). The compressor will maintain the pipework and air storage tanks in your system between two pressure limits. Fixed speed compressors have three conditions, on-load when they are producing air, off-load when they are not producing air and off when they are not used for a set period of time. This type of air compressor will remain on-load producing air until the tank and pipe-work reaches the desired pressure and then switch to light load. When running light load the air compressor produces no air and consumes less kW. The compressor will remain on light load until the system pressure drops to a specified minimum, at which point the compressor automatically cuts back in to get the system back up to pressure. If the system pressure does not reduce after a set period the compressor will automatically switch off. 

Variable Speed Drive Compressors

Variable speed drive compressors do not have these three states; they will run at a variable speed to maintain the system at a set pressure. The faster they run the more air they produce and they only consume power in proportion to the air delivered. As a consequence of this operation variable speed drive compressors will often reduce electricity consumption by 30% or more, although it does depend on the specifics of the system.