Buffer air method and system for a bearing compartment

An assembly for a turbine engine, comprising:

• a stationary structure forming a bearing compartment, a buffer cavity, a low pressure cavity and a high pressure cavity, the buffer cavity outboard of the bearing compartment, the low pressure cavity outboard of the buffer cavity, and the high pressure cavity outboard of the low pressure cavity;
• a vent line fluidly coupled with the low pressure cavity, the low pressure cavity configured to direct leakage air from the high pressure cavity and buffer air from the buffer cavity into the vent line as low pressure air;
• a valve fluidly coupled with and downstream of the vent line;
• and
• a control system configured to signal the valve to control venting of the low pressure air from the low pressure cavity through the vent line such that
• a pressure of the buffer air within the buffer cavity is maintained at or below a maximum buffer air threshold;
• and
• a flowrate of the leakage air across the buffer seal device is maintained at or above a minimum leakage air threshold.