A system and method for maintaining overpressure in a logging unit or other pressurized space through interruptions is disclosed. A backup air supply comprising tanks mounted to a frame is operatively connected to the ambient environment of the logging unit through a valve assembly which also connects a conventional pressure setup (e.g., pumps and filters from the external environment). The valve assembly comprises two auto valves, a shuttle valve, and a pressure sensor that allow the logging unit to switch from the conventional external air supply to the tanks when the pressure detected from the conventional air supply falls below a predetermined level. The valve assembly is independently housed and may be mounted or detached from the frame housing the backup tanks.