In one embodiment, a system includes a sight tube configured to optically communicate with an interior of a rotary machine via insertion within an inspection port. The sight tube includes a window and multiple openings configured to direct purge air across the window. The system also includes a curtain tube disposed about the sight tube and configured to direct purge air from a first air source to the openings via a first passage formed between an inner surface of the curtain tube and an outer surface of the sight tube. The curtain tube includes multiple outlets configured to direct curtain air around the window, and the curtain tube is configured to direct the curtain air from a second air source to the outlets via a second passage formed between an outer surface of the curtain tube and an inner surface of the inspection port.