Abstract: A system for the in-situ purification and monitoring of the condition of a lubricant fluid used in a rotary screw or centrifugal air compressor is described. The system is functionally incorporated into the rotary screw or centrifugal air compressor and comprises at least one filter device capable of removing an acid from the lubricant fluid, an electrical probe for electronically monitoring the condition of the lubricating fluid and communicating electrical signal to an electrical signal processing means, and an electrical signal processing means for processing electrical signal received from the electrical probe and alerting to the need for the change of the filter device or the lubricating fluid.