K911 - Positive Pressure - Demand Apparatus Ours consist of a direct connection to the face air assembly from surface. The pressure-demand apparatus provides positive pressure to the face piece during both inhalation and exhalation. Assuring clean breathable air from surface ^Everyone deserves to come home and share a meal with their loves ones! - Eric Bourque - President From a miner. Specifically designed for underground mines where compressed air is used.